Week 3 quiz on ch 3 and ch 11

Week 3 quiz on ch 3 and ch 11 


Use ch 3 and ch 11, Lectures 1 and 2 and related ppt to help you complete this quiz.


[back to week 3 activities]

Attempt History

Score for this quiz: 57 out of 80
Submitted Sep 7 at 6:53am
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Question 1

10 / 10 pts

1) Explain why the shipbuilder in “The Ethics of belief” by William Clifford, acted unethically.

2) What if the shipbuilder had formed a valid argument such as:

If a ship is safe, then one can responsibly let is sail.

This ship is safe.

Therefore, I can let it sail.

How would you respond to this in light of this week’s course content?

3) Imagine if Clifford had been alive during the peak of the pandemic. What might he have said about the belief “I believe that people don’t need to wear face covering or face masks when going into public spaces, like restaurants?:” How would this situation be similar to the case of the shipbuilder?


Your Answer:

Question 1

The shipbuilder acted unethically for the following reasons. First, the premises he made regarding the safety, reliability, and efficacy of the ship were not only unacceptable but questionable. For example, the shipbuilder did believe in whatever he wanted to believe regarding the ship’s reliability, even without adequate evidence. In practice, the shipbuilder openly acknowledged that the ship was old and inadequate to overcome the pressures and constraints in the high waters. Equally, the ultimate decision by the shipbuilder to allow the voyage into the sea was not informed by sufficient information on the ship’s current status. Hence, it was morally wrong to believe that the “unseaworthy” ship was bound to make a successful voyage despite being not well-built and old.

The formation of a deductive argument may have enabled the shipbuilder to lay bare the facts of the situation and to come up with reasoned and well-measured solutions to the ethical dilemmas he experienced. Similarly, following the line of thought presented in the ontological argument, the shipbuilder would have been able to identify how mechanical problems and technical issues surrounding the ship might have necessitated the need to stop the voyage due to the eminent reality of looming dangers and risks.

Question 2

The argument was that there wasn’t enough evidence to back up the ships’ readiness to sail and safety. The foundation is inadequate since it assumes that a ship can only sail if it is safe. Some further justifications should at least support the statement that we are safe. Therefore, since it can influence one’s conduct, it is a belief that shouldn’t be promoted.

Question 3

The wearing of facemasks at the peak of the COVID-19 pandemic was one of the key government-led containment measures to reduce the spread and transmission of coronavirus. A key comment from Clifford might be that the statement does not meet the three conditions for credibility. Precisely, the belief is not supported by proper empirical and conceptual evidence, it is biased, and it is perpetuated deliberately to deceive others from not doing the right thing, wearing facemasks to avert the effects of the COVID-19 pandemic.


Question 2

/ 4 pts

Which of the following definitions best fits the text’s description of validity?

A valid argument is one with true premises.

A valid argument is one with true premises and a true conclusion.


A valid argument is one where if the premises are true the conclusion has to be true as well.

A valid argument is one where if the premises are false, the conclusion can’t be true.

Question 3

/ 4 pts

Which of the following cannot be true of valid arguments?

Valid arguments cannot have false premises

Valid arguments cannot have false conclusions while its premises are false

You Answered

Valid arguments cannot have true conclusions while its premises are false.

Correct Answer

Valid arguments cannot have false conclusions while its premises are true.

Question 4

/ 4 pts

Suppose someone were to make this argument:

The moon is made of green cheese and whatever is made of green cheese orbits the earth. Therefore the moon orbits the earth.

Assume the person is attempting to make a deductive argument. In light of ch 3, and the notion of “validity,” which of the following points does this argument best exhibit about such arguments?.

Deductive arguments are usually about the moon.

Correct Answer

Deductively valid arguments can have true conclusions and false premises

You Answered

Deductively valid arguments can’t have true conclusions and false premises.

Some deductive arguments are invalid

Question 5

/ 4 pts

A sound deductive argument (also sometimes called a cogent deductive argument ) is an argument which is both valid and has true premises




Question 6

/ 12 pts

Use the handout “Conditonal argument forms” and the ppt slides on valid and invalid conditional arguments to determine if the following four deductive arguments are valid or invalid. Indicate in each case, why the argument is valid (modus ponens, modus tollens), or invalid (denies antecedent; affirms the consequent).  Be sure to pay attention to conclusion and premise indicator words.

1. If the car starts, then the battery must be working.  My car will not start. Hence, the battery must not be working.

2. If the car starts,, then the battery must be working.  So, the battery must be working, since the car starts.

3. The car has started, and that’s because the battery is in fact working.  And everyone knows that if the car starts, then the battery must be working.

4. The battery is not working, so the car won’t start, because if the car starts, then the battery must be working.

Your Answer:


  1. If the car starts, then the battery must be working.  My car will not start. Hence, the battery must not be working.

Valid argument (Modus Tollens)

  1. If the car starts, then the battery must be working.  So, the battery must be working, since the car starts.

Valid argument (Modus Ponens)

  1. The car has started, and that’s because the battery is in fact working.  And everyone knows that if the car starts, then the battery must be working.

Invalid (affirms the consequent)

  1. The battery is not working, so the car won’t start, because if the car starts, then the battery must be working.

Invalid (denies antecedent)

1 invalid – denies antecedent – 2 4 valid modus tollens – 2

Question 7

/ 4 pts

“People with lung cancer frequently have a history of smoking. Bill is a smoker, so he has a higher risk of getting lung cancer.”

This argument is:

You Answered

a valid deductive argument

a invalid deductive argument

an unsuccessful nondeductive argument which might be successful or not

Correct Answer

a successful nondeductive argument

notice the conclusion is a matter of probability

Question 8

/ 4 pts

Consider this argument:  90 % of Webster students work, Bill is a Webster student. Therefore he probably works.”  What sort of argument is this?

a plausibility argument

An inductive generalization


A statistical syllogism

An argument by analogy

Question 9

/ 4 pts

Suppose a neuroscientist is trying to understand how on average older adult brains work. Suppose they base their research on observing various brain scans in a large population of older adults and then draw conclusions from this. Such an argument would be a kind of

A valid deductive argument


inductive generalization

statistical syllogism

argument by analogy

Question 10

/ 8 pts

Using the narrow concept of acceptability ch 11 and the Lecture develops, determine if the following statements are a) self-evidently or analytically true; b) self-evidently or analytically false; c) neither self-evidently true nor false; d) conceptually incoherent (= nonsense)

See pg 190 for comparable exercises.

1. Gun control laws may lower fire arm deaths.

2. Ineffective gun control laws are effective

3. Strict gun control laws are strict.

4. Gun control is about 50 miles an hour slower than pure methane.

5. GPS technology works just in case GPS technology works.

6. GPS technology smirks smells beltways traffic.

7.  After GPS technology becomes a standard feature on rental cars, people will never get lost.

8. GPS technology never makes people happy and it always makes people happy.




Your Answer:


  1. Gun control laws may lower fire arm deaths.

Self-evidently or analytically true

  1. Ineffective gun control laws are effective

Conceptually incoherent (= nonsense)

  1. Strict gun control laws are strict.

Neither self-evidently true nor false

  1. Gun control is about 50 miles an hour slower than pure methane.

Conceptually incoherent (= nonsense)

  1. GPS technology works just in case GPS technology works.

Neither self-evidently true nor false

  1. GPS technology smirks smells beltways traffic.

Self-evidently or analytically false;

  1. After GPS technology becomes a standard feature on rental cars, people will never get lost.

Self-evidently or analytically true

  1. GPS technology never makes people happy and it always makes people happy.

Conceptually incoherent (= nonsense)

1 c – gun control laws might not be enforced, or might be poorly written 2 b (self-contradictory) 3 a- this is a tautology 5 a a tautology 6 d 8 b

Question 11

12 / 12 pts

Read this story in the New York Times (Links to an external site.). (It’s been fact-checked and is accurate.)

If you can’t access the web version of this article, here is a version of the article 

copied into a word document

Question to answer:

1)What general conclusions about Wei-Hock Soon does the article draw?

2)Even though does Wei-Hock Soon has a Ph.D. and is a scientist, why is not a credible expert on climate change in terms of the knowledge criteria of expertise?

3) What aspects of Soon’s relationship to the corporate world throw doubt on his trustworthiness as an expert on climate change?

4)What other observations do you have after reading this article?  (optional)

Your Answer:

1) What general conclusions about Wei-Hock Soon does the article draw?

The general conclusion made about Wei-Hock Soon (also known as Willie) is that he had deliberately allowed vested interests to influence his scientific research on the impact of greenhouse gases on climate change and global warming. The findings in the article indicated that Willie, a scientist at the Harvard-Smithsonian Center for Astrophysics, had violated the hallmarks of ethical research by failing to be transparent and impartial regarding his scientific research and its findings. Secondly, Willie violated the scientific disclosure policy by not revealing the funding he had received from key players in the fossil-fuel industry. This is a serious allegation since Wei-Hock Soon is accused of not upholding scientific integrity and objectivity of research publications by not disclosing his relationship with fossil fuel companies fully. Therefore, the accusation that Will is alleged to have a conflict itself puts doubt on the overall credibility of his research publications in the presence of a financial or commercial relationship construed as a potential conflict of interest.

2) Even though does Wei-Hock Soon has a Ph.D. and is a scientist, why is not a credible expert on climate change in terms of the knowledge criteria of expertise?

First, Wei-Hock has failed to demonstrate authority on matters related to the contributions of human activity to the problem of climate change and global warming. As such, his failure to adhere to the standards set in the conflict of interest scientific disclosure clearly indicates that he may be motivated by financial considerations, which puts immense doubt on his reputation as an objective and impartial scientist. Secondly, while Wei-Hock Soon may claim to have requisite educational qualifications, his attempt to create distinct insights through his scientific research has been widely discredited as hot air. Therefore, the controversial narrative of climate change denial advanced in the writings of Wei-Hock Soon appears to isolate him from the rest of the scientific community.

3) What aspects of Soon’s relationship with the corporate world throw doubt on his trustworthiness as an expert on climate change?

First, Soon’s relationship with the corporate world is confidential and hidden. This is because the allegations against him are brought to the limelight following many years of investigations by leading advocacy groups such as Greenpeace. Secondly, Wei-Hock Soon violated research and publication ethics by failing to disclose the possible conflict of interest in several published papers. Thirdly, undeclared financial conflicts may be apparent since Wei-Hock Soon had failed to share relevant funding information, which significantly undermines the credibility of the author, the journals, and the scientific research itself.

4) What other observations do you have after reading this article?  (optional)

The disclosure of conflict of interest in scientific publications is an important step aimed at upholding transparency, objectivity, and impartiality. Researchers and authors must take appropriate measures to avoid bias and subjectivity and maintain integrity, credibility, and transparency in developing, reporting, and publishing research findings.

Question 12

10 / 10 pts

Identify a website that is credible and a website that is not credible.   Using the criteria supplied in week three (see the Lecture on Acceptability), focus on three or four traits that each website has that make it credible or not credible.  (100 -150 words)

Your Answer:

Information found on credible and trustworthy websites is accurate and reliable. Additionally, some of the sources have undergone peer review; as a result, the information comes from authors whose work has been adjudged to be of high quality. Educational institutions’ websites like webster.edu are an illustration of trustworthy websites. Websites that lack credibility are those whose information cannot be relied upon or trusted since some of it may be fraudulent. Wikipedia is an example of a website that lacks credibility since some of the sites it links to are questionable. The presence of the date in websites, which enables users to decide whether the content is current enough for their objectives, is one characteristic that lends credibility to websites. Including sources of information on the website and citations of those sources is another indicator of a trustworthy website. Credible websites have a good design, which makes information easier to obtain. A website that lacks references for its material and has poor spelling and punctuation is one sign that it is unreliable. Unreliable websites do not identify the authors of the presentations, which is a good sign that the data is unreliable.

CREDIBLE: https://www.doi.gov/library/internet/climate (Links to an external site.)

  • Owned and updated by the U.S. Department of the Interior
  • Provides verifiable, reputable news and information on climate change-related topics
  • High credibility of the information sources annexed on the website.

NOT CREDIBLE: https://www.heartland.org/Center-Climate-Environment/ (Links to an external site.)

  • Lacks reputation for integrity due to financial considerations resulting from its active involvement in anti-climate change communication and promotion of climate change skepticism.
  • Lacks reputation for accuracy due to the controversial and unpopular content posted on the site about the role of greenhouse gases in the climate change crisis.
  • The use of questionable expertise on climate change topics undermines the credibility and validity of the research findings on this website.

Question 13

/ 0 pts
What questions and observations did this weeks content (readings and media) raise for you?

Your Answer:

  • How can climate change researchers and scientists conduct ethical research?
  • How can individuals avoid the effects of unethical decisions and/or actions?

Key observations included the critical importance of the conflict of interest scientific disclosure in promoting transparency and impartiality in scientific research. Equally, the centrality of having valid arguments stood out as essential to ensuring proper decision-making and problem-solving, particularly in complex, uncertain contexts.

Here, Goldstein argues that one of the reasons that 2/3 people don’t save for old age is that it is hard for us to connect between our present self and our future self.

Look at the video below:

https://www.ted.com/talks/daniel_goldstein_the_battle_between_your_present_and_future_self (Links to an external site.)

Here, Goldstein argues that one of the reasons that 2/3 people don’t save for old age is that it is hard for us to connect between our present self and our future self.

“You are basically two persons: your present self and your future self”, according to Goldstein. Your present self listens to the here and now, wants to satisfy his needs immediately. Your future self also wants to live and would like your present self to be a little wiser. So, opposing interests. The power of Now vs the importance of Future.

Here are a couple of written articles that relate to Goldstein’s research:

https://www.cnbc.com/2019/06/19/save-more-for-retirement-by-saying-hello-to-your-future-self.html (Links to an external site.)

https://www.cnbc.com/2019/07/25/the-selfie-that-could-make-you-a-rich-retiree.html (Links to an external site.)     this selfie could help turn things around

Question: the last article above, “this selfie could help turn things  around”, suggests that using virtual software such as FaceApp (or Oldify or AgingBooth) to produce an aged photo of yourself 40 years from now will motivate you to save more for retirement. Thinking about yourself, do you agree that looking at an aged photo of yourself will motivate you to save more? Why or why not?

The Critical Path (CP) project methodology helps to determine the sequence of dependent tasks allowing project managers to better prioritize, build schedules, and more.

In response to your peers, note the points upon which you agree and diverge regarding a particular methodology and discuss those points. Again, support your position with specific examples from your own experience or from your research.


Colton Brannon

The Critical Path (CP) project methodology helps to determine the sequence of dependent tasks allowing project managers to better prioritize, build schedules, and more. Dependent tasks, meaning tasks that are required before another task can begin, can fall into the categories of finish to start, finish to finish, start to start, and start to finish. These phrases identify the order of tasks to be completed and affect the start of each task. A few advantages of this method include easier prioritization, better risk detection, and the ability to adapt. Since it is understood which tasks have to be completed before starting another, they can be prioritized. Additionally, risks can be clear since they know which path the project will be following along. Finally, with CP allows for the schedule to be changed, if necessary, with the ability to see outcomes and make the best decision. Some disadvantages include complexity and applicability. The CP method revolves around many tasks and moving pieces requiring difficult calculations and the ability for human error. On the other hand, this method is not for every project. If there is not a clear structure to completing the project, this method may not be useful (Ramos, 2022).

The Critical Chain (CC) methodology is similar to CP as it focuses on the series of dependent tasks that must be completed for a project to be successful. The CC method, however, focuses on resources to buffer the timeline and therefore determines a success factor on the usefulness of these buffered resources. This method can be useful in reducing the time and cost of a project while allowing for problems to be detected quickly. Advantages include accelerating execution and reducing capital needs while disadvantages may include difficulty to grasp and required dedication. Overall CP and CC are similar, but CC operates with buffers and revolves more strongly around resources (Hlioui, 2020).

The third method agile, allows for continuous customer involvement through incremental delivery of project demands. This method is beneficial when there is uncertainty, unknowns, and room to work. By working with the client often things can be changed quickly to reflect the wants and needs from the customer. Agile advantages include fewer wasted resources, quick feedback, and the ability to experiment or create new ideas. Some of the disadvantages include increased effort due to constant interaction, inability to multitask projects due to constant attention needed on agile, and lack of design or knowledge of the project (Olic, 2020).

The criteria for the methods above can be unique to each situation as the task at hand and knowledge known differs every time. CP is often linked to construction projects as construction have concrete steps that have to be followed to achieve success. For example, the foundation has to be completed before building upon it as these are dependent tasks. CC is similar but can have a wide array of projects as well. Additionally, agile is often considered for IT projects as it allows for creative minds to work and develop new ideas, however, it is moving along to many projects nowadays. Overall, each method must be carefully considered with each task as the usual situation that these methods are used in can differ at any time. If used correctly for the correct situation there is great benefit for the customer and project management team.




Hlioui, O. (2020, December 11). The “Critical Chain Project Management ” approach (CCPM) -. cooens.com. Retrieved September 14, 2022, from https://cooens.com/knowledge-base/the-critical-chain-project-management-approach-ccpm/

Olic, A. (2020, October 28). Advantages and disadvantages of agile project management [checklist] · activecollab. ActiveCollab. Retrieved September 14, 2022, from https://activecollab.com/blog/project-management/agile-project-management-advantages-disadvantages

Ramos, D. (2022, May 5). Advantages & disadvantages of critical path method. Smartsheet. Retrieved September 14, 2022, from https://www.smartsheet.com/content/critical-path-advantages-disavantages


Response –

Emily Plante

Picking the right project management methodology is critical for executing a project successfully. There are many different methodologies that have their advantages and disadvantages. Three of these include Critical Path, Agile, and Waterfall. At the very core these methodologies are the same, they are ways of organizing a project’s sequence of events. Essentially, how the project will move from step A to step B (Westland, 2022). It’s their differences that really set them apart.

The waterfall approach is known as the most straightforward methodology. This approach flows down with each step, meaning that one step must be completed before the next one can start. This gives a very clear order of events. However, it does not allow for a lot of additional room for adjustments if needed (Westland, 2022). On the opposite end, the agile approach allows a lot of room for adjustments. This approach could be seen as more casual than the strict step to step approach of the waterfall methodology. An agile approach is fluid, there is an order of steps and what needs to happen to reach each milestone, but the order and timing of these steps is flexible. They can be moved around, sped up, or slowed down if needed (Westland, 2022).

The critical path method falls somewhere in between. The CPM takes a detailed look into each step, the amount of time needed, and compiles it into an estimate of the longest possible amount of time it would take to complete the project (Westland, 2022). It brings together the strictness of the waterfall approach by solidifying the steps and time, but there is room for flexibility as the CPM is the longest amount of time needed. Because of this, steps have the potential to be moved around and still stay within the timeframe (Westland, 2022).



What methodology is used is very dependent on the project and the project environment. For example, industries where an agile methodology works well is anything in tech, automotive, or music. These industries are always looking for the next big improvement and the agile method allows them flexibility with their projects (Westland, 2022). CPM and waterfall methodologies can both be used for smaller projects that are also very structured, construction for example (Westland, 2022). These projects tend to have a very set order of events and it could be costly for a project to deviate from the set plan. A small housing development would benefit from either method.

A small project I worked on while working in retail was a complete overhaul of the store and its products in between seasons. The waterfall methodology most closely resembled how we got the project done. We would stay after the store closed and follow a set structure of steps to get everything done. First we would work at the front of the store, take down and pack away displays and clothes not included in the new season, then refill that section starting with hanging clothes and moving to folded clothes and displays. From there we would move to the middle section, follow the same steps, and then the back sections of the store. With everyone knowing the exact steps and order it was accomplished efficiently and quickly. There was no wasted time trying to figure out who was working where and what product they needed.




Westland, J. (2022, May 20). Top 10 project management methodologies: An overview. Project Manager. Retrieved September 13, 2022, from https://www.projectmanager.com/blog/project-management-methodology

PSYC515 Research: Intro and Method Assignment Instructions


Research: Intro and Method Assignment Instructions



This is the first written component of your research project. Review all relevant files / presentations as listed in the Research Project Overview and this document. This project will refine your graduate level writing abilities and allow you to practice scientific writing skills. It also requires you to locate and read many research articles over a specific topic, discern which are most relevant, and use them to provide a review of literature while simultaneously building an argument for your proposed research study. This type of writing takes many revisions, so do not wait until the last minute to begin work on this assignment. (You are turning in a “final version” – not a draft!).



By this stage you should have already been approved to use your survey to collect data. You will now write the introduction and method sections of your research paper, transcribe your data to an SPSS file, and submit both for instructor feedback. Please read this document in its entirety before beginning this portion of your research project. There are three stages to this assignment as detailed below. This is the ONLY assignment in which you submit two separate files – you will also submit your SPSS data file within a single submission in Canvas. The entire assignment is worth a total of 60 points: up to 42 points are awarded based on correct content in both the word document and SPSS data file, and up to 18 points are awarded for structure in both the word document and SPSS data file. Submission instructions are reiterated at the bottom of these instructions.


The following stages are provided to help guide you through this assignment.


Stage 1: Read articles to locate the most relevant ones specific to your research project. You’ve already designed your survey based on previously validated scales or approved variables and copied the Reference entries from the Survey Instructions document. You can now locate those articles in the Jerry Falwell library to read to better understand those variables. (Note: for the first variable there was a citation – Hodge, 2003, Underwood, 2011, or Pargament et al., 2011; not all second variables had a reference provided).


In addition to the 1 – 2 articles used to validate your survey, you will need to find a minimum of FOUR additional articles that provide sufficient background to justify your research study. Thus, you will have a minimum of 5 – 6 articles discussed in your Introduction and included in your References for this phase. For the four articles you must find on your own:

· All should be from peer-reviewed journals. For a description of types of articles, please review Section 1 in the APA Manual.

· At least three of the articles should report primary, empirical, quantitative research; no more than one can be a literature review/theoretical/ or meta-analysis article. Discussion of the articles must include enough information to clearly identify what type of article is being discussed.

· All four articles should be used to provide context and justification for your study – thus, their relevance to your study must be clear. Each article does not have to be related to both of your chosen variables and they do not have to use the same scales as the ones you selected, but each should be clearly related to at least one of the constructs of interest in your study. All should be discussed in such as a way that methods and results are sufficiently described and relevance to your study is clear. Conclusions from the four studies you selected must form a foundation for understanding the merits of your study.


Stage 2: Write the following portions of your research paper: Introduction, Method, References, Appendix. Make sure you follow the APA guidelines for a professional paperThe following steps outline the systematic organization of the body within each of these sections.

1) Introduction: remember you use the title of the paper in title case, bold, and centered (2.11; Figure 2.4). Also include a running head and page numbers. Note both the title and running head should reflect your study’s topic – NOT that is it a phase or part of a class. You are already expected to be able to write at the graduate level in terms of grammar, syntax, and using your own words (no quotes or just switching out a few words – you must reword ideas and summarize other research). However, we are now also honing scientific writing skills. Thus, there is no page or word minimum. Be concise yet detailed. Do not be redundant or opinionated. There is a specific flow to all quantitative research articles. The body of your introduction should contain the following information IN THIS ORDER:

a. Frame the importance of the problem (3.4) – begin by clarifying the objective – whether it be theoretical, potential application, input for public policy, et cet..

b. Discuss at least 5 relevant articles (1 – 2 related to your survey; four selected by you). Quotes are NOT allowed in this course – use your own words. This is to:

i. Provide a scope of the problem and its context

ii. Theoretical or practical implications

iii. Emphasize pertinent findings and major conclusions (make sure you use in-text citations and that all citations are included in the Reference section).

1. Describe similarities and differences among the research reviewed

2. Explain the relevance of each article to the proposed study

3. Discuss relevant methodological issues

c. Note: this section will be multiple paragraphs, but it should NOT consist of an article per paragraph – use the articles you’ve chosen to provide an overview of the problem and ultimately, to justify your research idea. Always use a topic sentence to express the main idea for each paragraph (topic sentences rarely include citations). If the next paragraph does not flow easily, use a transition sentence at the end of the previous paragraph.

d. In the final paragraph of your introduction (and NOT before this!), state the purpose and rationale for your proposed study.

i. State the problem (which is always a lack of information or contradictory findings in the field) and a rationale for further exploration. (This should be justified based on what you wrote in earlier paragraphs).

ii. End the Introduction by explicitly stating the alternate hypothesis (people do not state the null hypothesis in research articles, although remember that is what you are statistically testing!!). You also do not write the words “alternate hypothesis”. Rather, you can write something along the lines of “It is predicted that there is a relationship” or “It is hypothesized that there is a difference…”

iii. Remember “relationship” implies one type of statistical test whereas “difference” implies a different type of statistical test – so use the words to reflect what type of statistical test you’ll conduct!

2) Method: Continue with your use of proper formatting, noting that the Method does not start on a new page, rather it begins immediately after the last sentence in your introduction. Don’t forget to use the APA Manual as a guide. Level 2 headings for your Method section must include (in this order and in APA format):

a. Participants – include the number of participants, a description of the participants, and sampling procedures

b. Materials – include a description of the survey questions used, including citations where appropriate (e.g., if you use spirituality you should cite Hodge, 2003). Don’t include assumed items (e.g., pencils to complete a survey).

c. Procedure – summarizes where the study took place (e.g., church, small group, Facebook) and the experience of the participants in a detailed and organized manner – this will be very short.

d. Analysis – state how the variables are operationally defined (e.g., responses to the seven questions affiliated with anxiety are averaged, ranging from 1 – 7, with higher numbers indicating greater anxiety), alpha value (we always use 0.05), what statistical test will be used to answer the research question (e.g., independent samples t-test), and what version of SPSS is being used to analyze the data. Hint: Due to the brief nature of the course, the statistical test is most likely one reviewed in the first few weeks of PSYC 515 that was covered also in PSYC 510.

3) References: 5-6 entries minimum following guidelines stated above. Use Sections 9 – 10 in the APA Manual for proper formatting.

4) Appendix: Include a copy of your approved survey in an Appendix as the last page of your single word document (see Section 2 in the APA Manual).


Stage 3: Data entry in SPSS

· Every single question from your survey must be clearly labeled and entered into SPSS in addition to your final calculated variables. Although you may not use all of this data in your analysis, it is imperative as it allows the instructor to ensure your calculations were correct.

· For instance, you may have six questions for the construct “spirituality”. However, none of these would be used in your SPSS analysis – you are to average them (per directions in the Research Project Survey Instructions file from Module 1). In your SPSS data file, I would expect to see the individual answers to all six of these questions PLUS an averaged spirituality column. All columns must be labeled to clearly identify what they are related to (e.g, spirituality1; spirituality2; AveSpirituality). You will only use the “AveSpirituality” column for statistical analyses but all are required in this assignment to ensure the variable was correctly combined. Failure to include all participant answers will result in a significant deduction of points on this assignment.

· Refer to the Survey Data Compilation Instructions document in this week’s Module for an example of how to go from data collection to combining all surveys into SPSS for data analysis. This document has three completed example surveys and then pictures of how the data entry would look in SPSS in both Data and Variable Views.

· Note in this example, the survey is comprised of nine questions. All 9 questions would be individually represented in the SPSS file with descriptive names (NOT Q1, Q2, et cet). Since questions 3 – 9 in this example survey are about anxiety, they could be named Anxiety1, Anxiety2, et cet. However, all of these questions are concerning ONE construct – anxiety. In this instance, anxiety was calculated by totaling responses from all 7 questions related to anxiety and then multiplied by 2. Therefore, the SPSS data file for this assignment would need to have 10 columns of data (1 demographic, 1 for organizational religiosity, and 8 for anxiety).


Submission Instructions. You will be submitting TWO files:

1. Word document (.doc or .docx) containing an Introduction, Method, References, and Appendix (survey)

2. SPSS data file with all data from every question on the survey PLUS any reserve scored, summed, averaged, et cet variables (.sav)


Note: Your assignment will be checked for originality via the Turnitin plagiarism tool.



Page 2 of 2


Research: Research Design Assignment Instructions


This is the first assignment in your Research Project. The purpose is to scaffold the process of designing and conducting a research study. In this first phase, you will submit a research proposal and survey by completing this form. Your instructor will review this form and provide feedback to let you know if you are approved to collect data using the survey submitted as part of this assignment (you should create your survey at the end of this document).


Be sure you have reviewed this module’s assigned readings and presentations before completing this assignment. Of most relevance is the Research Project Overview and Research Project Survey Instructions documents in this week’s Learn section. This assignment is worth 40 points: 36 points for content and 4 points based on format. Each question is worth 2 content points. Format is for completing answers within the assigned sections and for proper format of the survey. Note that until the survey is approved by your instructor you cannot move forward with the future assignments associated with the Research Project. Turning in this assignment late, incomplete, or inaccurately formatted may impact performance on future portions of this project.

· There are two parts to this assignment:

· Research Design: complete the table below by placing answers where indicated (“<ANSWER>”).

· Survey: at the end of this document (where it says <Create Proposed Survey Here> create a proposed survey. It should be formatted to be easy for a person to read and complete. You must create the survey in its entirety within this document – you cannot copy / paste question(s) as an image as distortion may occur (you must retype them). All questions should be the same font and font size. Make sure there is uniformity in appearance and there are no typos.

· You will submit this assignment as a single word document by the due date in Canvas.


Research Design Table
Demographic Variable Name of variable: Participant age.
  Levels of variable you will use: 20-50
  Scale of Measurement (nominal, ordinal, or scale): Scale
  Appropriate measure of central tendency and (if appropriate) variability: Mean
Variable of Interest #1 Name of variable and/or scale selected (including citation): Religious Reflections Scale
  How many questions? What are the answer options – e.g., Likert 1 – 5?): Survey enables this study to predict specific categories. The use of a Likert Scale will facilitate the necessary categories in this process. Six questions will be provided with a scale from 1-10.
  How is this variable quantified? What is the potential numerical range and how is it interpreted? (i.e. how do you calculate the variable as a single numerical value to be used in SPSS for data analysis) Notes: if it is only one question, the answer will be similar to what you have as the previous answer; if scale is nominal, numbers are meaningless but necessary for SPSS so you won’t discuss the numbers in your paper but will state them here. In each of the six questions the score for all the questions will be averaged together to present a specific number using SPSS.
  What is its scale of measurement? The scores will range from 0 (not spiritual) to 10 (extremely spiritual).
Variable of Interest #2 Name of variable and/or scale selected (including citation if appropriate): Conscious Reflections
  How many questions? What are the answer options – e.g., Likert 1 – 5?: Quantitative
  How is this variable quantified? What is the potential numerical range and how is it interpreted? (i.e. how do you calculate the variable as a single numerical value to be used in SPSS for data analysis) Notes: if it is only one question, the answer will be similar to what you have as the previous answer; if scale is nominal, numbers are meaningless but necessary for SPSS so you won’t discuss the numbers in your paper but will state them here. In eleven of the questions, a numerical score for each question will be tallied then averaged to provide a specific numerical value using SPSS.
  What is its scale of measurement? Scores will be between 1and 5.

The scale of measurement will be interval.

Research Design Correlational, quasi-experimental, or experimental (since you have 2 variables it will NOT be descriptive): Predictive.
  Justification: Personal spirituality will affect each person’s life based on surroundings, the media, and society.
Research / Alternate Hypothesis (note this is NOT the null hypothesis). **It is common practice in the field to explicitly state the research hypothesis in the paper but statistically test the null hypothesis.
Information will be collected based on each person’s inner reflections of thoughts and feelings.


Proposed Target Population (e.g., “friends” on facebook; only women, colleagues at a specific type of business – note you will need 20 participants from this target population, and you cannot use people you do not know due to the educational nature of this study and our IRB exempt status constraints – read the M2 Research Data Collection Instructions for further clarification):
Facebook; Friends.


Proposed survey distribution method (e.g., email, facebook, hand out paper surveys at your church, et cet – note you cannot distribute these in public places due to the exempt status of this educational assignment – read the M2 Research Data Collection Instructions for further clarification):


At the end of this document (starting on the next page), create a proposed survey making sure to include the following components:

· Disclaimer

· Directions to the participant on how to answer the questions (may need directions for each subsection)

· Question(s) related to the Demographic Variable

· Question(s) related to Variable 1

· Question(s) related to Variable 2





This is a survey of spirituality. Please take a moment to answer the following questions. The information that you provide is being collected for research purposes and will not be shared. This information being collected is strictly confidential. In order to participate in this survey, you must be between the age of 20 and 50. Please circle the most appropriate answer that you feel is appropriate for you.


Background Questions



a. What is your Age?





B. Variable Testing: Reflections of Inner Thoughts & Feelings


The following questions are designed to indicate how relevant religion and spirituality is in your life. It will indicate how important God is to you and your family daily. This is indicated by 0, a least amount, and 10, the greatest amount.


1. Religion and spirituality are important in my life.


0 1 2 3 4 5 6 7 8 9 10


None Very Important



2. Spiritual grow this important.

0 1 2 3 4 5 6 7 8 9 10


None Most Important


3. I use my relationship with God to answer questions in my life.

0 1 2 3 4 5 6 7 8 9 10

None Very Important




4. Spirituality is a motivating force in my life.


0 1 2 3 4 5 6 7 8 9 10


No part of my life Very Important



5. When I think of the things that help me grow and mature as a person.


0 1 2 3 4 5 6 7 8 9 10


None Very Important


6. God is important in my life.


0 1 2 3 4 5 6 7 8 9 10


No part of my life Very Important Part




C. Inner Conscious Thoughts Scale (5-Point Response Scale). Circle One:


7. It is important to constantly be learning


1 2 3 4 5


Strongly Disagree Strongly Agree



8. Recognizing details is important.


1 2 3 4 5


Strongly Disagree Strongly Agree



9. Everyone one has a voice and opinion.


1 2 3 4 5


Strongly Disagree Strongly Agree



10. I value other people’s thoughts and opinions.


1 2 3 4 5


Strongly Disagree Strongly Agree



11. My family has taught me that life is a journey and a constant learning process.


1 2 3 4 5


Strongly Disagree Strongly Agree



12. I listen and have developed a respect for others.


1 2 3 4 5


Strongly Disagree Strongly Agree



13. I feel a connection with strangers

1 2 3 4 5


Strongly Disagree Strongly Agree



14. I think things through before I make a decision.


1 2 3 4 5


Strongly Disagree Strongly Agree



15. I have become a valued member of society.


1 2 3 4 5


Strongly Disagree Strongly Agree


16. I understand others and their points of view.


1 2 3 4 5


Strongly Disagree Strongly Agree



17. I apply my intelligence when encountering a problem.


1 2 3 4 5


Strongly Disagree Strongly Agree



18. I understand people of other races.


1 2 3 4 5


Strongly Disagree Strongly Agree



19. I listen to others before I make a decision


1 2 3 4 5


Strongly Disagree Strongly Agree



20. Over the duration of my life, I have used God as a means of guidance and spirituality.


1 2 3 4 5


Strongly Disagree Strongly Agree





Note: Your assignment will be checked for originality via the Turnitin plagiarism tool.

Page 2 of 2

Before you begin this assignment, review the Occupational Safety and Health Administration’s (OSHA) Hazard Communication Standard, 29 CFR §1910.1200.

Before you begin this assignment, review the Occupational Safety and Health Administration’s (OSHA) Hazard Communication Standard, 29 CFR §1910.1200. After you have reviewed the webpage above, imagine that you have been asked to present to the senior leadership team at a chemical manufacturing company. The goal of the presentation is to inform senior leadership about OSHA Hazard Communication regulations so they can develop a hazardous communications program for their company.In a PowerPoint presentation, address the areas below.

  • Explain what the purpose of OSHA is and why it is important for leadership to know about it.
  • Explain how the OSHA Hazard Communication Standard is used to manage hazardous substances.
  • Explain why laws, regulations, and standards need to be considered when drafting a communications program.
  • Provide an example of the steps that leadership should take to develop their hazardous communications program at their company.

Your PowerPoint presentation must be at least 10 slides in length, not counting the title slide and references slide. Support your presentation with at least two references. Use APA Style for in-text citations and references. Your references can include but are not limited to the textbook or any OSHA websites. Support your presentation with at least two images or graphics. Speaker notes are not required for this assignment.

Which form of cellular adaptation occurs because of decreased work demands on the cell? Explain your answer.

Which form of cellular adaptation occurs because of decreased work demands on the cell? Explain your answer.
A. Hypertrophy

B. Hyperplasia

C. Atrophy

D. Metaplasia

Reply to this post with 250 words, no plagiarism please.

The answer is C, Atrophy. Atrophy is a kind of celular adaptation mechanism in which the celular size decrease due to a reduction in the consumption of all kind of nutrients, a reduction on the celular demand/metabolic requirements for several etiologic factors. For instance, a marked decrease of total muscular mass, can be observed on clients with long periods of illness recovery due to lack of organ (muscles) use.

Part 1: Ethical and legal aspect of nursing

Part 1: Ethical and legal aspect of nursing


1. Introduction (One paragraph)

2. What is human rights in nursing (One paragraph)

3. Role of the nurse as advocacy of human rights in clinical practice ( Two paragraphs)

4. Scope nurse as advocacy of human rights in clinical practice ( Two paragraphs)

5. What are the important things that must be kept in mind while practicing human rights as a nurse? (Nine paragraphs: fours paragraphs for “a”, four for “b” and one paragraph for “c”: Total nine paragraphs)

a. Describe ( not list) a minimum of 4 things and explain them

b. link between practice nurse and these 4 things

c. Nurse limitation to practicing human rights as a health professional.

6. Describe a proposal to break or reduce the limitations of nurses described in question 4  (One paragraph)

7. Reflection  (One paragraph)

8. Conclusion  (One paragraph)

Part 2: Nursing leadership

Topic: Nurse Leader Interview

Designated specialty role: Nursing Director,

Interview (in person, face to face) a leader relevant to the designated specialty role of choice that would hire a Master of Science prepared nurse (Advanced Practice Nurse) in your specialty. The nurse leader interview will be developed into an APA formatted paper.

1. Brief introduction of the leader being interviewed, including (One paragraph):

a. Brief biography of the interviewee

b. Organization represented (Miami).

c. Explain why this individual was chosen for the interview in light of your selected nursing specialty role.

2. A Learning Conversation, state each question you posed along with the interviewee’s responses (Nine paragraphs. One paragraph per each question: Total nine paragraphs)

a. Determine from the interviewee what are the mission/vision/ goals of the organization.

b. Describe the interviewee’s expectations of an advanced practice nurse- a leader within his, or her specialty.

c. Discuss what the interviewee believes it takes for the Bachelor of Science prepared nurse to academically excel at the advanced practice nursing level

d. Discuss what the interviewee believes it takes to transition to a nurse leader in this organization.

d. Discuss what the interviewee believes about what is be a leader

e. Discuss what the interviewee believes it takes to be a good leader

f. Discuss what the interviewee believes it takes for  attempt to transition into new specialty nursing

g. Discuss what the interviewee believes about the advantages of transition into a new organization

h. Discuss what the interviewee believes about the added improvement in the skills and competencies professional of transition into new specialty nursing for the nurses

3. Reflection and Follow-Up (One paragraph).

a. Make a critical analysis and evaluation of the interview process including

b. What would you do differently?

c. Please include resultant plans (post-interview) for professional development and pursuit of future nurse leader opportunities.

4. Summary (One paragraph)

a. Summarize the key points of the conversation as each relates to the interviewee’s chosen nursing leadership-specialty role

b.How a prospective nurse leader could make a successful transition to such a role within the selected nurse leader’s organization.

Effective Leadership Skills Necessary for Leadership Issues instead of Management Issues

Effective Leadership Skills Necessary for Leadership Issues instead of Management Issues

Leadership is the art of effecting radical, transformative change through forethought, vision, and strategy. Key leadership characteristics include inspiring followers and making quick, flexible choices. On the other hand, management entails carrying out regular, scheduled operations with the assistance of subordinates. The manager’s exclusive responsibility is to carry out the four core managerial tasks of planning, controlling, leading, and organizing (Duggal, 2022). One of the essential qualities in a leader that will enable them to spend more time on leadership issues and less time on management issues is the capacity to convey ideas directly and diplomatically. There is more to effective communication than just hearing others out and reacting thoughtfully. Being explicit about what you want and need, clarifying misunderstandings, and providing helpful information are all components of effective communication. The most effective leaders are also excellent communicators, using their words to motivate and enliven their teams (Nawaz & Khan, 2016). Another skill is inspiring and motivating their teams by their motivation, inspiration, and motivation. Take the time to get to know the people under your leadership so you can better understand their skill sets, challenges, and goals. Not only will they appreciate the effort, but you’ll also gain insight into how to inspire them to do better. Keep reminding them how their hard work is helping, and push them to reach their full potential by setting ambitious but achievable goals and providing them with challenging yet achievable obstacles. Leaders are concerned with boosting morale and inspiring their followers. Leaders seek to instill a sense of urgency in their followers to take risks in pursuing shared objectives and challenge the status quo (Wajdi, 2017).


Management as an Art and Science

Management is interdisciplinary, encompassing elements of both science and art. It is classified as a science because of its systematic approach to knowledge acquisition and the presence of objective truths within its body of knowledge. Management is often considered an art form since every manager relies on their unique experiences and expertise in their work. Science provides knowledge, whereas art is concerned with applying skills and knowledge (O’Hare, 2010). Managers need management so that they may use their intuitions, judgments, and “gut feelings” in addition to the theories and evidence they have studied in the past when making decisions. Managers need “conceptual skills,” or the ability to think critically and develop novel solutions to their organizations’ problems. The process of translating abstract notions and ideas into a workable strategy for implementation is commonly referred to as planning. Therefore, the ability to conceptualize the plan’s potential benefits and drawbacks is also necessary. Second, managers must have humanity skills, including communication and interpersonal relational abilities. Humanity’s abilities include good communication with others, such as when managers collaborate with and engage with their staff. Managers who can persuade and connect with their teams personally are more likely to have their efforts rewarded with greater enthusiasm and success (Setiawan, n.d).

Covey’s (1991) Approach to Resolving Managerial Issues

Managerial issues entail matters that require decision, investigation, or action, such as disciplinary procedures, complaints, absence of the intern, periods of sick or annual leave, awards of benefits and payment, performance issues, and company induction procedures. According to Covey (1991), one of the approaches to resolving managerial issues is promoting a habit of mutual gain. Win/Win is a mental and emotional state that seeks mutual gain in all human interactions. Win/win solutions or agreements are mutually beneficial and pleasant. With a win-win solution, all stakeholders are satisfied with the decision and devoted to the action plan. Win-win agreements clearly define desired outcomes, instructions for achieving those outcomes, resources available, accountability metrics, and punishments (Covey, 1991). The same holds for efficient risk management. The group’s leaders want their employees to have a teachable attitude that places a premium on helping each other out rather than putting the spotlight on who’s at fault. Possibilities and dangers can each be assigned owners in a risk register. At this point, management may decide to fund certain initiatives or mitigating measures. The risk management procedure emphasizes loops of feedback, standards, responsibility, and repercussions. Win-win techniques foster a positive working relationship amongst all parties involved in a negotiation. In a win-win negotiation, all sides believe they can work toward a mutual gain. This common objective permits each participant in a win-win negotiation to collaborate, and they may explore future collaboration with the other party (Indeed Editorial Team, 2021)

First, consider how the Trojan war started, and explain whether or not you think this was a legitimate reason to go to war with someone. What does this reveal about the way men think about and/or treat women?

This is a multistep prompt in which you have to answer each of the questions posed to you.

First, consider how the Trojan war started, and explain whether or not you think this was a legitimate reason to go to war with someone. What does this reveal about the way men think about and/or treat women?

Next, what is your impression of the heroes you’ve read about for this week? In answering this part of the prompt, you can compare and contrast the Greek heroes versus the Trojan heroes. For example, Achilles, Patroclus, Agamemnon, and Menelaus versus Hector and Paris. Do you think their behaviors are honorable or dishonorable? Explain, using examples and/or quotes from the text to support your answer.


· Your initial response should be at least 500 words in length

· Use MLA format for any quotations or citations that you use to support your answer


Hamilton, Edith. Mythology: Timeless Tales of Gods and Heroes. Grand Central Publishing, 2011.

· Part Four: The Heroes of the Trojan War, pp. 253 to 344

· Part Five: The Great Families of Mythology: The House of Atreus, pp 345 to 372

 Additional Resources

YouTube Video

· Troy: Fall of a City | Official Trailer [HD] | Netflix

Think about the effects of global warming and pick one event, such as an extreme weather incident. How might this affect public health?

100 words each APA format

1: FQ2

Think about the effects of global warming and pick one event, such as an extreme weather incident. How might this affect public health? Utilizing the information that you have learned in this week’s lesson (reading and lectures), combined with your own knowledge and experiences, compose your answer- ( I will attach one of the readings)

6: FQ

Why didn’t banning the super gulp (large size soft drinks) work in New York City?

Prof. Timetest
Review Assessing ‘‘Dangerous Climate Change’’: Required Reduction of Carbon Emissions to Protect Young People, Future Generations and Nature James Hansen 1*, Pushker Kharecha 1,2 , Makiko Sato 1, Valerie Masson-Delmotte 3, Frank Ackerman 4, David J. Beerling 5, Paul J. Hearty 6, Ove Hoegh-Guldberg 7, Shi-Ling Hsu 8, Camille Parmesan 9,10 , Johan Rockstrom 11, Eelco J. Rohling 12,13 , Jeffrey Sachs 1, Pete Smith 14, Konrad Steffen 15, Lise Van Susteren 16, Karina von Schuckmann 17, James C. Zachos 18 1Earth Institute, Columbia University, New York, New York, United States of America,2Goddard Institute for Space Studies, NASA, New York, New York, United States of America,3Institut Pierre Simon Laplace, Laboratoire des Sciences du Climat et de l’Environnement (CEA-CNRS-UVSQ), Gif-sur-Yvette, France,4Synapse Energy Economics, Cambridge, Massachusetts, United States of America,5Department of Animal and Plant Sciences, University of Sheffield, Sheffield, South Yorkshire, United Kingdom, 6Department of Environmental Studies, University of North Carolina, Wilmington, North Carolina, United States of America,7Global Change Institute, University of Queensland, St. Lucia, Queensland, Australia,8College of Law, Florida State University, Tallahassee, Florida, United States of America,9Marine Institute, Plymouth University, Plymouth, Devon, United Kingdom,10Integrative Biology, University of Texas, Austin, Texas, United States of America,11Stockholm Resilience Center, Stockholm University, Stockholm, Sweden,12School of Ocean and Earth Science, University of Southampton, Southampton, Hampshire, United Kingdom,13Research School of Earth Sciences, Australian National University, Canberra, ACT, Australia,14University of Aberdeen, Aberdeen, Scotland, United Kingdom,15Swiss Federal Institute of Technology, Swiss Federal Research Institute WSL, Zurich, Switzerland,16Center for Health and the Global Environment, Advisory Board, Harvard School of Public Health, Boston, Massachusetts, United States of America,17L’Institut Francais de Recherche pour l’Exploitation de la Mer, Ifremer, Toulon, France,18Earth and Planetary Science, University of California, Santa Cruz, CA, United States of America Abstract: We assess climate impacts of global warming using ongoing observations and paleoclimate data. We use Earth’s measured energy imbalance, paleoclimate data, and simple representations of the global carbon cycle and temperature to define emission reductions needed to stabilize climate and avoid potentially disas- trous impacts on today’s young people, future genera- tions, and nature. A cumulative industrial-era limit of ,500 GtC fossil fuel emissions and 100 GtC storage in the biosphere and soil would keep climate close to the Holocene range to which humanity and other species are adapted. Cumulative emissions of,1000 GtC, sometimes associated with 2uC global warming, would spur ‘‘slow’’ feedbacks and eventual warming of 3–4uC with disastrous consequences. Rapid emissions reduction is required to restore Earth’s energy balance and avoid ocean heat uptake that would practically guarantee irreversible effects. Continuation of high fossil fuel emissions, given current knowledge of the consequences, would be an act of extraordinary witting intergenerational injustice. Re- sponsible policymaking requires a rising price on carbon emissions that would preclude emissions from most remaining coal and unconventional fossil fuels and phase down emissions from conventional fossil fuels. Introduction Humans are now the main cause of changes of Earth’s atmospheric composition and thus the drive for future climate change [1]. The principal climate forcing, defined as an imposed change of planetary energy balance [1–2], is increasing carbon dioxide (CO 2) from fossil fuel emissions, much of which will remain in the atmosphere for millennia [1,3]. The climate response to this forcing and society’s response to climate change are complicated by the system’s inertia, mainly due to the ocean and the ice sheets on Greenland and Antarctica together with the long residence time of fossil fuel carbon in the climate system. Theinertia causes climate to appear to respond slowly to this human- made forcing, but further long-lasting responses can be locked in. More than 170 nations have agreed on the need to limit fossil fuel emissions to avoid dangerous human-made climate change, as formalized in the 1992 Framework Convention on Climate Change [6]. However, the stark reality is that global emissions have accelerated (Fig. 1) and new efforts are underway to massively expand fossil fuel extraction [7–9] by drilling to increasing ocean depths and into the Arctic, squeezing oil from tar sands and tar shale, hydro-fracking to expand extraction of natural gas, developing exploitation of methane hydrates, and mining of coal via mountaintop removal and mechanized long- wall mining. The growth rate of fossil fuel emissions increased from 1.5%/year during 1980–2000 to 3%/year in 2000–2012, mainly because of increased coal use [4–5]. The Framework Convention [6] does not define a dangerous level for global warming or an emissions limit for fossil fuels. The Citation:Hansen J, Kharecha P, Sato M, Masson-Delmotte V, Ackerman F, et al. (2013) Assessing ‘‘Dangerous Climate Change’’: Required Reduction of Carbon Emissions to Protect Young People, Future Generations and Nature. PLoS ONE 8(12): e81648. doi:10.1371/journal.pone.0081648 Editor:Juan A. An˜ el, University of Oxford, United Kingdom PublishedDecember 3, 2013 This is an open-access article, free of all copyright, and may be freely reproduced, distributed, transmitted, modified, built upon, or otherwise used by anyone for any lawful purpose. The work is made available under the Creative Commons CC0 public domain dedication. Funding:Funding came from: NASA Climate Research Funding, Gifts to Columbia University from H.F. (‘‘Gerry’’) Lenfest, private philanthropist (no web site, but see http://en.wikipedia.org/wiki/H._F._Lenfest), Jim Miller, Lee Wasser- man (Rockefeller Family Fund) (http://www.rffund.org/), Flora Family Foundation (http://www.florafamily.org/), Jeremy Grantham, ClimateWorks and the Energy Foundation provided support for Hansen’s Climate Science, Awareness and Solutions program at Columbia University to complete this research and publication. The funders had no role in study design, data collection and analysis, decision to publish, or preparation of the manuscript. Competing Interests:The authors have declared that no competing interests exist. * E-mail: [email protected] PLOS ONE | www.plosone.org 1 December 2013 | Volume 8 | Issue 12 | e81648 European Union in 1996 proposed to limit global warming to 2uC relative to pre-industrial times [10], based partly on evidence that many ecosystems are at risk with larger climate change. The 2uC target was reaffirmed in the 2009 ‘‘Copenhagen Accord’’ emerging from the 15th Conference of the Parties of the Framework Convention [11], with specific language ‘‘We agree that deep cuts in global emissions are required according to science, as documented in the IPCC Fourth Assessment Report with a view to reduce global emissions so as to hold the increase in global temperature below 2 degrees Celsius…’’. A global warming target is converted to a fossil fuel emissions target with the help of global climate-carbon-cycle models, which reveal that eventual warming depends on cumulative carbon emissions, not on the temporal history of emissions [12]. The emission limit depends on climate sensitivity, but central estimates [12–13], including those in the upcoming Fifth Assessment of the Intergovernmental Panel on Climate Change [14], are that a 2uC global warming limit implies a cumulative carbon emissions limit of the order of 1000 GtC. In comparing carbon emissions, note that some authors emphasize the sum of fossil fuel and deforestation carbon. We bookkeep fossil fuel and deforestation carbon separately, because the larger fossil fuel term is known more accurately and this carbon stays in the climate system for hundreds of thousands of years. Thus fossil fuel carbon is the crucial human input that must be limited. Deforestation carbon is more uncertain and potentially can be offset on the century time scale by storage in the biosphere, including the soil, via reforestation and improved agricultural and forestry practices. There are sufficient fossil fuel resources to readily supply 1000 GtC, as fossil fuel emissions to date (370 GtC) are only a small fraction of potential emissions from known reserves and potentially recoverable resources (Fig. 2). Although there are uncertainties in reserves and resources, ongoing fossil fuel subsidies and continuing technological advances ensure that more and more of these fuels will be economically recoverable. As we will show, Earth’s paleoclimate record makes it clear that the CO 2produced by burning all or most of these fossil fuels would lead to a very different planet than the one that humanity knows. Our evaluation of a fossil fuel emissions limit is not based on climate models but rather on observational evidence of global climate change as a function of global temperature and on the factthat climate stabilization requires long-term planetary energy balance. We use measured global temperature and Earth’s measured energy imbalance to determine the atmospheric CO 2 level required to stabilize climate at today’s global temperature, which is near the upper end of the global temperature range in the current interglacial period (the Holocene). We then examine climate impacts during the past few decades of global warming and in paleoclimate records including the Eemian period, concluding that there are already clear indications of undesirable impacts at the current level of warming and that 2uC warming would have major deleterious consequences. We use simple representations of the carbon cycle and global temperature, consistent with observations, to simulate transient global temper- ature and assess carbon emission scenarios that could keep global climate near the Holocene range. Finally, we discuss likely over- shooting of target emissions, the potential for carbon extraction from the atmosphere, and implications for energy and economic policies, as well as intergenerational justice. Global Temperature and Earth’s Energy Balance Global temperature and Earth’s energy imbalance provide our most useful measuring sticks for quantifying global climate change and the changes of global climate forcings that would be required to stabilize global climate. Thus we must first quantify knowledge of these quantities. Temperature Temperature change in the past century (Fig. 3; update of figures in [16]) includes unforced variability and forced climate change. The long-term global warming trend is predominantly a forced climate change caused by increased human-made atmospheric gases, mainly CO 2[1]. Increase of ‘‘greenhouse’’ gases such as CO 2 has little effect on incoming sunlight but makes the atmosphere more opaque at infrared wavelengths, causing infrared (heat) radiation to space to emerge from higher, colder levels, which thus reduces infrared radiation to space. The resulting planetary energy imbalance, absorbed solar energy exceeding heat emitted to space, causes Earth to warm. Observations, discussed below, confirm that Earth is now substantially out of energy balance, so the long-term warming will continue. Figure 1. CO 2annual emissions from fossil fuel use and cement manufacture, based on data of British Petroleum[4]concatenated with data of Boden et al.[5].(A) is log scale and (B) is linear. doi:10.1371/journal.pone.0081648.g001Assessing Dangerous Climate Change PLOS ONE | www.plosone.org 2 December 2013 | Volume 8 | Issue 12 | e81648 Global temperature appears to have leveled off since 1998 (Fig. 3a). That plateau is partly an illusion due to the 1998 global temperature spike caused by the El Nin˜ o of the century that year. The 11-year (132-month) running mean temperature (Fig. 3b) shows only a moderate decline of the warming rate. The 11-year averaging period minimizes the effect of variability due to the 10– 12 year periodicity of solar irradiance as well as irregular El Nin˜o/ La Nin˜ a warming/cooling in the tropical Pacific Ocean. The current solar cycle has weaker irradiance than the several prior solar cycles, but the decreased irradiance can only partially account for the decreased warming rate [17]. Variability of the El Nin˜ o/La Nin˜ a cycle, described as a Pacific Decadal Oscillation, largely accounts for the temporary decrease of warming [18], as we discuss further below in conjunction with global temperature simulations.Assessments of dangerous climate change have focused on estimating a permissible level of global warming. The Intergov- ernmental Panel on Climate Change [1,19] summarized broad- based assessments with a ‘‘burning embers’’ diagram, which indicated that major problems begin with global warming of 2– 3uC. A probabilistic analysis [20], still partly subjective, found a median ‘‘dangerous’’ threshold of 2.8uC, with 95% confidence that the dangerous threshold was 1.5uC or higher. These assessments were relative to global temperature in year 1990, so add 0.6uC to these values to obtain the warming relative to 1880– 1920, which is the base period we use in this paper for preindustrial time. The conclusion that humanity could tolerate global warming up to a few degrees Celsius meshed with common sense. After all, people readily tolerate much larger regional and seasonal climate variations. Figure 2. Fossil fuel CO 2emissions and carbon content (1 ppm atmospheric CO 2,2.12 GtC).Estimates of reserves (profitable to extract at current prices) and resources (potentially recoverable with advanced technology and/or at higher prices) are the mean of estimates of Energy Information Administration (EIA) [7], German Advisory Council (GAC) [8], and Global Energy Assessment (GEA) [9]. GEA [9] suggests the possibility of .15,000 GtC unconventional gas. Error estimates (vertical lines) are from GEA and probably underestimate the total uncertainty. We convert energy content to carbon content using emission factors of Table 4.2 of [15] for coal, gas and conventional oil, and, also following [15], emission factor of unconventional oil is approximated as being the same as for coal. Total emissions through 2012, including gas flaring and cement manufacture, are 384 GtC; fossil fuel emissions alone are,370 GtC. doi:10.1371/journal.pone.0081648.g002 Figure 3. Global surface temperature relative to 1880–1920 mean.B shows the 5 and 11 year means. Figures are updates of [16] using data through August 2013. doi:10.1371/journal.pone.0081648.g003Assessing Dangerous Climate Change PLOS ONE | www.plosone.org 3 December 2013 | Volume 8 | Issue 12 | e81648 The fallacy of this logic emerged recently as numerous impacts of ongoing global warming emerged and as paleoclimate implications for climate sensitivity became apparent. Arctic sea ice end-of-summer minimum area, although variable from year to year, has plummeted by more than a third in the past few decades, at a faster rate than in most models [21], with the sea ice thickness declining a factor of four faster than simulated in IPCC climate models [22]. The Greenland and Antarctic ice sheets began to shed ice at a rate, now several hundred cubic kilometers per year, which is continuing to accelerate [23–25]. Mountain glaciers are receding rapidly all around the world [26–29] with effects on seasonal freshwater availability of major rivers [30–32]. The hot dry subtropical climate belts have expanded as the troposphere has warmed and the stratosphere cooled [33–36], contributing to increases in the area and intensity of drought [37] and wildfires [38]. The abundance of reef-building corals is decreasing at a rate of 0.5–2%/year, at least in part due to ocean warming and possibly ocean acidification caused by rising dissolved CO 2[39– 41]. More than half of all wild species have shown significant changes in where they live and in the timing of major life events [42–44]. Mega-heatwaves, such as those in Europe in 2003, the Moscow area in 2010, Texas and Oklahoma in 2011, Greenland in 2012, and Australia in 2013 have become more widespread with the increase demonstrably linked to global warming [45–47]. These growing climate impacts, many more rapid than anticipated and occurring while global warming is less than 1uC, imply that society should reassess what constitutes a ‘‘dangerous level’’ of global warming. Earth’s paleoclimate history provides a valuable tool for that purpose. Paleoclimate Temperature Major progress in quantitative understanding of climate change has occurred recently by use of the combination of data from high resolution ice cores covering time scales of order several hundred thousand years [48–49] and ocean cores for time scales of order one hundred million years [50]. Quantitative insights on global temperature sensitivity to external forcings [51–52] and sea level sensitivity to global temperature [52–53] are crucial to our analyses. Paleoclimate data also provide quantitative information about how nominally slow feedback processes amplify climate sensitivity [51–52,54–56], which also is important to our analyses. Earth’s surface temperature prior to instrumental measurements is estimated via proxy data. We will refer to the surface temperature record in Fig. 4 of a recent paper [52]. Global mean temperature during the Eemian interglacial period (120,000 years ago) is constrained to be 2uC warmer than our pre-industrial (1880–1920) level based on several studies of Eemian climate [52]. The concatenation of modern and instrumental records [52] is based on an estimate that global temperature in the first decade of the 21st century (+0.8uC relative to 1880–1920) exceeded the Holocene mean by 0.2560.25uC. That estimate was based in part on the fact that sea level is now rising 3.2 mm/yr (3.2 m/ millennium) [57], an order of magnitude faster than the rate during the prior several thousand years, with rapid change of ice sheet mass balance over the past few decades [23] and Greenland and Antarctica now losing mass at accelerating rates [23–24]. This concatenation, which has global temperature 13.9uC in the base period 1951–1980, has the first decade of the 21st century slightly (,0.1uC) warmer than the early Holocene maximum. A recent reconstruction from proxy temperature data [55] concluded that global temperature declined about 0.7uC between the Holocene maximum and a pre-industrial minimum before recent warming brought temperature back near the Holocene maximum, which is consistent with our analysis.Climate oscillations evident in Fig. 4 of Hansen et al. [52] were instigated by perturbations of Earth’s orbit and spin axis tilt relative to the orbital plane, which alter the geographical and seasonal distribution of sunlight on Earth [58]. These forcings change slowly, with periods between 20,000 and 400,000 years, and thus climate is able to stay in quasi-equilibrium with these forcings. Slow insolation changes initiated the climate oscillations, but the mechanisms that caused the climate changes to be so large were two powerful amplifying feedbacks: the planet’s surface albedo (its reflectivity, literally its whiteness) and atmospheric CO 2 amount. As the planet warms, ice and snow melt, causing the surface to be darker, absorb more sunlight and warm further. As the ocean and soil become warmer they release CO 2and other greenhouse gases, causing further warming. Together with fast feedbacks processes, via changes of water vapor, clouds, and the vertical temperature profile, these slow amplifying feedbacks were responsible for almost the entire glacial-to-interglacial temperature change [59–62]. The albedo and CO 2feedbacks amplified weak orbital forcings, the feedbacks necessarily changing slowly over millennia, at the pace of orbital changes. Today, however, CO 2is under the control of humans as fossil fuel emissions overwhelm natural changes. Atmospheric CO 2has increased rapidly to a level not seen for at least 3 million years [56,63]. Global warming induced by increasing CO 2will cause ice to melt and hence sea level to rise as the global volume of ice moves toward the quasi-equilibrium amount that exists for a given global temperature [53]. As ice melts and ice area decreases, the albedo feedback will amplify global warming. Earth, because of the climate system’s inertia, has not yet fully responded to human-made changes of atmospheric composition. The ocean’s thermal inertia, which delays some global warming for decades and even centuries, is accounted for in global climate models and its effect is confirmed via measurements of Earth’s energy balance (see next section). In addition there are slow climate feedbacks, such as changes of ice sheet size, that occur mainly over centuries and millennia. Slow feedbacks have little effect on the immediate planetary energy balance, instead coming into play in response to temperature change. The slow feedbacks are difficult to model, but paleoclimate data and observations of ongoing changes help provide quantification. Earth’s Energy Imbalance At a time of climate stability, Earth radiates as much energy to space as it absorbs from sunlight. Today Earth is out of balance because increasing atmospheric gases such as CO 2reduce Earth’s heat radiation to space, thus causing an energy imbalance, as there is less energy going out than coming in. This imbalance causes Earth to warm and move back toward energy balance. The warming and restoration of energy balance take time, however, because of Earth’s thermal inertia, which is due mainly to the global ocean. Earth warmed about 0.8uC in the past century. That warming increased Earth’s radiation to space, thus reducing Earth’s energy imbalance. The remaining energy imbalance helps us assess how much additional warming is still ‘‘in the pipeline’’. Of course increasing CO 2is only one of the factors affecting Earth’s energy balance, even though it is the largest climate forcing. Other forcings include changes of aerosols, solar irradiance, and Earth’s surface albedo. Determination of the state of Earth’s climate therefore requires measuring the energy imbalance. This is a challenge, because the imbalance is expected to be only about 1 W/m 2or less, so accuracy approaching 0.1 W/m 2is needed. The most promising Assessing Dangerous Climate Change PLOS ONE | www.plosone.org 4 December 2013 | Volume 8 | Issue 12 | e81648 approach is to measure the rate of changing heat content of the ocean, atmosphere, land, and ice [64]. Measurement of ocean heat content is the most critical observation, as nearly 90 percent of the energy surplus is stored in the ocean [64–65]. Observed Energy Imbalance Nations of the world have launched a cooperative program to measure changing ocean heat content, distributing more than 3000 Argo floats around the world ocean, with each float repeatedly diving to a depth of 2 km and back [66]. Ocean coverage by floats reached 90% by 2005 [66], with the gaps mainly in sea ice regions, yielding the potential for an accurate energy balance assessment, provided that several systematic measurement biases exposed in the past decade are minimized [67–69]. Argo data reveal that in 2005–2010 the ocean’s upper 2000 m gained heat at a rate equal to 0.41 W/m 2averaged over Earth’s surface [70]. Smaller contributions to planetary energy imbalance are from heat gain by the deeper ocean (+0.10 W/m 2), energy used in net melting of ice (+0.05 W/m 2), and energy taken up by warming continents (+0.02 W/m 2). Data sources for these estimates and uncertainties are provided elsewhere [64]. The resulting net planetary energy imbalance for the six years 2005– 2010 is+0.5860.15 W/m 2. The positive energy imbalance in 2005–2010 confirms that the effect of solar variability on climate is much less than the effect of human-made greenhouse gases. If the sun were the dominant forcing, the planet would have a negative energy balance in 2005– 2010, when solar irradiance was at its lowest level in the period of accurate data, i.e., since the 1970s [64,71]. Even though much of the greenhouse gas forcing has been expended in causing observed 0.8uC global warming, the residual positive forcing overwhelms the negative solar forcing. The full amplitude of solar cycle forcing is about 0.25 W/m 2[64,71], but the reduction of solar forcing due to the present weak solar cycle is about half that magnitude as we illustrate below, so the energy imbalance measured during solar minimum (0.58 W/m 2) suggests an average imbalance over the solar cycle of about 0.7 W/m 2. Earth’s measured energy imbalance has been used to infer the climate forcing by aerosols, with two independent analyses yielding a forcing in the past decade of about21.5 W/m 2[64,72], including the direct aerosol forcing and indirect effects via induced cloud changes. Given this large (negative) aerosol forcing, precisemonitoring of changing aerosols is needed [73]. Public reaction to increasingly bad air quality in developing regions [74] may lead to future aerosol reductions, at least on a regional basis. Increase of Earth’s energy imbalance from reduction of particulate air pollution, which is needed for the sake of human health, can be minimized via an emphasis on reducing absorbing black soot [75], but the potential to constrain the net increase of climate forcing by focusing on black soot is limited [76]. Energy Imbalance Implications for CO 2Target Earth’s energy imbalance is the most vital number character- izing the state of Earth’s climate. It informs us about the global temperature change ‘‘in the pipeline’’ without further change of climate forcings and it defines how much greenhouse gases must be reduced to restore Earth’s energy balance, which, at least to a good approximation, must be the requirement for stabilizing global climate. The measured energy imbalance accounts for all natural and human-made climate forcings, including changes of atmospheric aerosols and Earth’s surface albedo. If Earth’s mean energy imbalance today is+0.5 W/m 2,CO 2 must be reduced from the current level of 395 ppm (global-mean annual-mean in mid-2013) to about 360 ppm to increase Earth’s heat radiation to space by 0.5 W/m 2and restore energy balance. If Earth’s energy imbalance is 0.75 W/m 2,CO 2must be reduced to about 345 ppm to restore energy balance [64,75]. The measured energy imbalance indicates that an initial CO 2 target ‘‘,350 ppm’’ would be appropriate, if the aim is to stabilize climate without further global warming. That target is consistent with an earlier analysis [54]. Additional support for that target is provided by our analyses of ongoing climate change and paleoclimate, in later parts of our paper. Specification now of a CO 2 target more precise than,350 ppm is difficult and unnecessary, because of uncertain future changes of forcings including other gases, aerosols and surface albedo. More precise assessments will become available during the time that it takes to turn around CO 2growth and approach the initial 350 ppm target. Below we find the decreasing emissions scenario that would achieve the 350 ppm target within the present century. Specifically, we want to know the annual percentage rate at which emissions must be reduced to reach this target, and the dependence of this rate upon the date at which reductions are initiated. This approach is complementary to the approach of estimating cumulative emissions allowed to achieve a given limit on global warming [12]. Figure 4. Decay of atmospheric CO 2perturbations.(A) Instantaneous injection or extraction of CO 2with initial conditions at equilibrium. (B) Fossil fuel emissions terminate at the end of 2015, 2030, or 2050 and land use emissions terminate after 2015 in all three cases, i.e., thereafter thereis no net deforestation. doi:10.1371/journal.pone.0081648.g004Assessing Dangerous Climate Change PLOS ONE | www.plosone.org 5 December 2013 | Volume 8 | Issue 12 | e81648 If the only human-made climate forcing were changes of atmospheric CO 2, the appropriate CO 2target might be close to the pre-industrial CO 2amount [53]. However, there are other human forcings, including aerosols, the effect of aerosols on clouds, non-CO 2greenhouse gases, and changes of surface albedo that will not disappear even if fossil fuel burning is phased out. Aerosol forcings are substantially a result of fossil fuel burning [1,76], but the net aerosol forcing is a sensitive function of various aerosol sources [76]. The indirect aerosol effect on clouds is non- linear [1,76] such that it has been suggested that even the modest aerosol amounts added by pre-industrial humans to an otherwise pristine atmosphere may have caused a significant climate forcing [59]. Thus continued precise monitoring of Earth’s radiation imbalance is probably the best way to assess and adjust the appropriate CO 2target. Ironically, future reductions of particulate air pollution may exacerbate global warming by reducing the cooling effect of reflective aerosols. However, a concerted effort to reduce non-CO 2 forcings by methane, tropospheric ozone, other trace gases, and black soot might counteract the warming from a decline in reflective aerosols [54,75]. Our calculations below of future global temperature assume such compensation, as a first approximation. To the extent that goal is not achieved, adjustments must be made in the CO 2target or future warming may exceed calculated values. Climate Impacts Determination of the dangerous level of global warming inherently is partly subjective, but we must be as quantitative as possible. Early estimates for dangerous global warming based on the ‘‘burning embers’’ approach [1,19–20] have been recognized as probably being too conservative [77]. A target of limiting warming to 2uC has been widely adopted, as discussed above. We suspect, however, that this may be a case of inching toward a better answer. If our suspicion is correct, then that gradual approach is itself very dangerous, because of the climate system’s inertia. It will become exceedingly difficult to keep warming below a target smaller than 2uC, if high emissions continue much longer. We consider several important climate impacts and use evidence from current observations to assess the effect of 0.8uC warming and paleoclimate data for the effect of larger warming, especially the Eemian period, which had global mean temperature about+2uC relative to pre-industrial time. Impacts of special interest are sea level rise and species extermination, because they are practically irreversible, and others important to humankind. Sea Level The prior interglacial period, the Eemian, was at most,2uC warmer than 1880–1920 (Fig. 3). Sea level reached heights several meters above today’s level [78–80], probably with instances of sea level change of the order of 1 m/century [81–83]. Geologic shoreline evidence has been interpreted as indicating a rapid sea level rise of a few meters late in the Eemian to a peak about 9 meters above present, suggesting the possibility that a critical stability threshold was crossed that caused polar ice sheet collapse [84–85], although there remains debate within the research community about this specific history and interpretation. The large Eemian sea level excursions imply that substantial ice sheet melting occurred when the world was little warmer than today. During the early Pliocene, which was only,3uC warmer than the Holocene, sea level attained heights as much as 15–25 meters higher than today [53,86–89]. Such sea level rise suggests that parts of East Antarctica must be vulnerable to eventual melting with global temperature increase of a few degrees Celsius. Indeed,satellite gravity data and radar altimetry reveal that the Totten Glacier of East Antarctica, which fronts a large ice mass grounded below sea level, is now losing mass [90]. Greenland ice core data suggest that the Greenland ice sheet response to Eemian warmth was limited [91], but the fifth IPCC assessment [14] concludes that Greenland very likely contributed between 1.4 and 4.3 m to the higher sea level of the Eemian. The West Antarctic ice sheet is probably more susceptible to rapid change, because much of it rests on bedrock well below sea level [92–93]. Thus the entire 3–4 meters of global sea level contained in that ice sheet may be vulnerable to rapid disintegration, although arguments for stability of even this marine ice sheet have been made [94]. However, Earth’s history reveals sea level changes of as much as a few meters per century, even though the natural climate forcings changed much more slowly than the present human-made forcing. Expected human-caused sea level rise is controversial in part because predictions focus on sea level at a specific time, 2100. Sea level on a given date is inherently difficult to predict, as it depends on how rapidly non-linear ice sheet disintegration begins. Focus on a single date also encourages people to take the estimated result as an indication of what humanity faces, thus failing to emphasize that the likely rate of sea level rise immediately after 2100 will be much larger than within the 21 stcentury, especially if CO 2 emissions continue to increase. Recent estimates of sea level rise by 2100 have been of the order of 1 m [95–96], which is higher than earlier assessments [26], but these estimates still in part assume linear relations between warming and sea level rise. It has been argued [97–98] that continued business-as-usual CO 2emissions are likely to spur a nonlinear response with multi-meter sea level rise this century. Greenland and Antarctica have been losing mass at rapidly increasing rates during the period of accurate satellite data [23]; the data are suggestive of exponential increase, but the records are too short to be conclusive. The area on Greenland with summer melt has increased markedly, with 97% of Greenland experiencing melt in 2012 [99]. The important point is that the uncertainty is not about whether continued rapid CO 2emissions would cause large sea level rise, submerging global coastlines – it is about how soon the large changes would begin. The carbon from fossil fuel burning will remain in and affect the climate system for many millennia, ensuring that over time sea level rise of many meters will occur – tens of meters if most of the fossil fuels are burned [53]. That order of sea level rise would result in the loss of hundreds of historical coastal cities worldwide with incalculable economic consequences, create hundreds of millions of global warming refugees from highly-populated low-lying areas, and thus likely cause major international conflicts. Shifting Climate Zones Theory and climate models indicate that the tropical overturn- ing (Hadley) atmospheric circulation expands poleward with global warming [33]. There is evidence in satellite and radiosonde data and in observational data for poleward expansion of the tropical circulation by as much as a few degrees of latitude since the 1970s [34–35], but natural variability may have contributed to that expansion [36]. Change in the overturning circulation likely contributes to expansion of subtropical conditions and increased aridity in the southern United States [30,100], the Mediterranean region, South America, southern Africa, Madagascar, and southern Australia. Increased aridity and temperature contribute to increased forest fires that burn hotter and are more destructive [38]. Assessing Dangerous Climate Change PLOS ONE | www.plosone.org 6 December 2013 | Volume 8 | Issue 12 | e81648 Despite large year-to-year variability of temperature, decadal averages reveal isotherms (lines of a given average temperature) moving poleward at a typical rate of the order of 100 km/decade in the past three decades [101], although the range shifts for specific species follow more complex patterns [102]. This rapid shifting of climate zones far exceeds natural rates of change. Movement has been in the same direction (poleward, and upward in elevation) since about 1975. Wild species have responded to climate change, with three-quarters of marine species shifting their ranges poleward as much as 1000 km [44,103] and more than half of terrestrial species shifting ranges poleward as much as 600 km and upward as much as 400 m [104]. Humans may adapt to shifting climate zones better than many species. However, political borders can interfere with human migration, and indigenous ways of life already have been adversely affected [26]. Impacts are apparent in the Arctic, with melting tundra, reduced sea ice, and increased shoreline erosion. Effects of shifting climate zones also may be important for indigenous Americans who possess specific designated land areas, as well as other cultures with long-standing traditions in South America, Africa, Asia and Australia. Human Extermination of Species Biodiversity is affected by many agents including overharvest- ing, introduction of exotic species, land use changes, nitrogen fertilization, and direct effects of increased atmospheric CO 2on plant ecophysiology [43]. However, an overriding role of climate change is exposed by diverse effects of rapid warming on animals, plants, and insects in the past three decades. A sudden widespread decline of frogs, with extinction of entire mountain-restricted species attributed to global warming [105– 106], provided a dramatic awakening. There are multiple causes of the detailed processes involved in global amphibian declines and extinctions [107–108], but global warming is a key contributor and portends a planetary-scale mass extinction in the making unless action is taken to stabilize climate while also fighting biodiversity’s other threats [109]. Mountain-restricted and polar-restricted species are particularly vulnerable. As isotherms move up the mountainside and poleward, so does the climate zone in which a given species can survive. If global warming continues unabated, many of these species will be effectively pushed off the planet. There are already reductions in the population and health of Arctic species in the southern parts of the Arctic, Antarctic species in the northern parts of the Antarctic, and alpine species worldwide [43]. A critical factor for survival of some Arctic species is retention of all-year sea ice. Continued growth of fossil fuel emissions will cause loss of all Arctic summer sea ice within several decades. In contrast, the scenario in Fig. 5A, with global warming peaking just over 1uC and then declining slowly, should allow summer sea ice to survive and then gradually increase to levels representative of recent decades. The threat to species survival is not limited to mountain and polar species. Plant and animal distributions reflect the regional climates to which they are adapted. Although species attempt to migrate in response to climate change, their paths may be blocked by human-constructed obstacles or natural barriers such as coast lines and mountain ranges. As the shift of climate zones [110] becomes comparable to the range of some species, less mobile species can be driven to extinction. Because of extensive species interdependencies, this can lead to mass extinctions. Rising sea level poses a threat to a large number of uniquely evolved endemic fauna living on islands in marine-dominated ecosystems, with those living on low lying islands being especiallyvulnerable. Evolutionary history on Bermuda offers numerous examples of the direct and indirect impact of changing sea level on evolutionary processes [111–112], with a number of taxa being extirpated due to habitat changes, greater competition, and island inundation [113]. Similarly, on Aldahabra Island in the Indian Ocean, land tortoises were exterminated during sea level high stands [114]. Vulnerabilities would be magnified by the speed of human-made climate change and the potentially large sea level rise [115]. IPCC [26] reviewed studies relevant to estimating eventual extinctions. They estimate that if global warming exceeds 1.6uC above preindustrial, 9–31 percent of species will be committed to extinction. With global warming of 2.9uC, an estimated 21–52 percent of species will be committed to extinction. A compre- hensive study of biodiversity indicators over the past decade [116] reveals that, despite some local success in increasing extent of protected areas, overall indicators of pressures on biodiversity including that due to climate change are continuing to increase and indicators of the state of biodiversity are continuing to decline. Mass extinctions occurred several times in Earth’s history [117– 118], often in conjunction with rapid climate change. New species evolved over millions of years, but those time scales are almost beyond human comprehension. If we drive many species to extinction we will leave a more desolate, monotonous planet for our children, grandchildren, and more generations than we can imagine. We will also undermine ecosystem functions (e.g., pollination which is critical for food production) and ecosystem resilience (when losing keystone species in food chains), as well as reduce functional diversity (critical for the ability of ecosystems to respond to shocks and stress) and genetic diversity that plays an important role for development of new medicines, materials, and sources of energy. Coral Reef Ecosystems Coral reefs are the most biologically diverse marine ecosystem, often described as the rainforests of the ocean. Over a million species, most not yet described [119], are estimated to populate coral reef ecosystems generating crucial ecosystem services for at least 500 million people in tropical coastal areas. These ecosystems are highly vulnerable to the combined effects of ocean acidification and warming. Acidification arises as the ocean absorbs CO 2, producing carbonic acid [120], thus making the ocean more corrosive to the calcium carbonate shells (exoskeletons) of many marine organ- isms. Geochemical records show that ocean pH is already outside its range of the past several million years [121–122]. Warming causes coral bleaching, as overheated coral expel symbiotic algae and become vulnerable to disease and mortality [123]. Coral bleaching and slowing of coral calcification already are causing mass mortalities, increased coral disease, and reduced reef carbonate accretion, thus disrupting coral reef ecosystem health [40,124]. Local human-made stresses add to the global warming and acidification effects, all of these driving a contraction of 1–2% per year in the abundance of reef-building corals [39]. Loss of the three-dimensional coral reef frameworks has consequences for all the species that depend on them. Loss of these frameworks also has consequences for the important roles that coral reefs play in supporting fisheries and protecting coastlines from wave stress. Consequences of lost coral reefs can be economically devastating for many nations, especially in combination with other impacts such as sea level rise and intensification of storms. Assessing Dangerous Climate Change PLOS ONE | www.plosone.org 7 December 2013 | Volume 8 | Issue 12 | e81648 Climate Extremes Changes in the frequency and magnitude of climate extremes, of both moisture and temperature, are affected by climate trends as well as changing variability. Extremes of the hydrologic cycle are expected to intensify in a warmer world. A warmer atmosphere holds more moisture, so precipitation can be heavier and cause more extreme flooding. Higher temperatures, on the other hand, increase evaporation and can intensify droughts when they occur, as can expansion of the subtropics, as discussed above. Global models for the 21st century find an increased variability of precipitation minus evaporation [P-E] in most of the world, especially near the equator and at high latitudes [125]. Some models also show an intensification of droughts in the Sahel, driven by increasing greenhouse gases [126]. Observations of ocean salinity patterns for the past 50 years reveal an intensification of [P-E] patterns as predicted by models, but at an even faster rate. Precipitation observations over land show the expected general increase of precipitation poleward of the subtropics and decrease at lower latitudes [1,26]. An increase of intense precipitation events has been found on much of the world’s land area [127–129]. Evidence for widespread drought intensification is less clear and inherently difficult to confirm with available data because of the increase of time-integrated precip- itation at most locations other than the subtropics. Data analyses have found an increase of drought intensity at many locations [130–131] The magnitude of change depends on the drought index employed [132], but soil moisture provides a good means to separate the effect of shifting seasonal precipitation and confirms an overall drought intensification [37]. Global warming of,0.6uC since the 1970s (Fig. 3) has already caused a notable increase in the occurrence of extreme summer heat [46]. The likelihood of occurrence or the fractional area covered by 3-standard-deviation hot anomalies, relative to a base period (1951– 1980) that was still within the range of Holocene climate, has increased by more than a factor of ten. Large areas around Moscow, the Mediterranean region, the United States and Australia have experienced such extreme anomalies in the past three years. Heat waves lasting for weeks have a devastating impact on human health: the European heat wave of summer 2003 caused over 70,000 excess deaths [133]. This heat record for Europe was surpassed already in 2010 [134]. The number of extreme heat waves has increased several-fold due to global warming [45–46,135] and will increase further if temperatures continue to rise. Human Health Impacts of climate change cause widespread harm to human health, with children often suffering the most. Food shortages, polluted air, contaminated or scarce supplies of water, an expanding area of vectors causing infectious diseases, and more intensely allergenic plants are among the harmful impacts [26]. More extreme weather events cause physical and psychological harm. World health experts have concluded with ‘‘very high confidence’’ that climate change already contributes to the global burden of disease and premature death [26]. IPCC [26] projects the following trends, if global warming continue to increase, where only trends assigned very high confidence or high confidence are included: (i) increased malnutrition and consequent disorders, including those related to child growth and development, (ii) increased death, disease and injuries from heat waves, floods, storms, fires and droughts, (iii) increased cardio-respiratory morbidity and mortality associated with ground-level ozone. While IPCC also projects fewer deaths from cold, this positive effect is far outweighed by the negative ones. Growing awareness of the consequences of human-caused climate change triggers anxiety and feelings of helplessness [136– 137]. Children, already susceptible to age-related insecurities, face additional destabilizing insecurities from questions about how they will cope with future climate change [138–139]. Exposure to media ensures that children cannot escape hearing that their future and that of other species is at stake, and that the window of opportunity to avoid dramatic climate impacts is closing. The psychological health of our children is a priority, but denial of the truth exposes our children to even greater risk. Health impacts of climate change are in addition to direct effects of air and water pollution. A clear illustration of direct effects of fossil fuels on human health was provided by an inadvertent experiment in China during the 1950–1980 period of central planning, when free coal for winter heating was provided to North China but not to the rest of the country. Analysis of the impact was made [140] using the most comprehensive data file ever compiled on mortality and air pollution in any developing country. A principal conclusion was that the 500 million residents of North China experienced during the 1990s a loss of more than 2.5 billion life years owing to the added air pollution, and an average reduction in life expectancy of 5.5 years. The degree of air pollution in China exceeded that in most of the world, yet Figure 5. Atmospheric CO 2if fossil fuel emissions reduced.(A) 6% or 2% annual cut begins in 2013 and 100 GtC reforestation drawdown occurs in 2031–2080, (B) effect of delaying onset of emission reduction. doi:10.1371/journal.pone.0081648.g005Assessing Dangerous Climate Change PLOS ONE | www.plosone.org 8 December 2013 | Volume 8 | Issue 12 | e81648 assessments of total health effects must also include other fossil fuel caused air and water pollutants, as discussed in the following section on ecology and the environment. The Text S1 has further discussion of health impacts of climate change. Ecology and the Environment The ecological impact of fossil fuel mining increases as the largest, easiest to access, resources are depleted [141]. A constant fossil fuel production rate requires increasing energy input, but also use of more land, water, and diluents, with the production of more waste [142]. The increasing ecological and environmental impact of a given amount of useful fossil fuel energy is a relevant consideration in assessing alternative energy strategies. Coal mining has progressively changed from predominantly underground mining to surface mining [143], including moun- taintop removal with valley fill, which is now widespread in the Appalachian ecoregion in the United States. Forest cover and topsoil are removed, explosives are used to break up rocks to access coal, and the excess rock is pushed into adjacent valleys, where it buries existing streams. Burial of headwater streams causes loss of ecosystems that are important for nutrient cycling and production of organic matter for downstream food webs [144]. The surface alterations lead to greater storm runoff [145] with likely impact on downstream flooding. Water emerging from valley fills contain toxic solutes that have been linked to declines in watershed biodiversity [146]. Even with mine-site reclamation intended to restore pre-mined surface conditions, mine-derived chemical constituents are found in domestic well water [147]. Reclaimed areas, compared with unmined areas, are found to have increased soil density with decreased organic and nutrient content, and with reduced water infiltration rates [148]. Reclaimed areas have been found to produce little if any regrowth of woody vegetation even after 15 years [149], and, although this deficiency might be addressed via more effective reclamation methods, there remains a likely significant loss of carbon storage [149]. Oil mining has an increasing ecological footprint per unit delivered energy because of the decreasing size of new fields and their increased geographical dispersion; transit distances are greater and wells are deeper, thus requiring more energy input [145]. Useful quantitative measures of the increasing ecological impacts are provided by the history of oil development in Alberta, Canada for production of both conventional oil and tar sands development. The area of land required per barrel of produced oil increased by a factor of 12 between 1955 and 2006 [150] leading to ecosystem fragmentation by roads and pipelines needed to support the wells [151]. Additional escalation of the mining impact occurs as conventional oil mining is supplanted by tar sands development, with mining and land disturbance from the latter producing land use-related greenhouse gas emissions as much as 23 times greater than conventional oil production per unit area [152], but with substantial variability and uncertainty [152–153]. Much of the tar sands bitumen is extracted through surface mining that removes the ‘‘overburden’’ (i.e., boreal forest ecosystems) and tar sand from large areas to a depth up to 100 m, with ecological impacts downstream and in the mined area [154]. Although mined areas are supposed to be reclaimed, as in the case of mountaintop removal, there is no expectation that the ecological value of reclaimed areas will be equivalent to predevelopment condition [141,155]. Landscape changes due to tar sands mining and reclamation cause a large loss of peatland and stored carbon, while also significantly reducing carbon sequestration potential [156]. Lake sediment cores document increased chemicalpollution of ecosystems during the past several decades traceable to tar sands development [157] and snow and water samples indicate that recent levels of numerous pollutants exceeded local and national criteria for protection of aquatic organisms [158]. Gas mining by unconventional means has rapidly expanded in recent years, without commensurate understanding of the ecological, environmental and human health consequences [159]. The predominant approach is hydraulic fracturing (‘‘frack- ing’’) of deep shale formations via injection of millions of gallons of water, sand and toxic chemicals under pressure, thus liberating methane [155,160]. A large fraction of the injected water returns to the surface as wastewater containing high concentrations of heavy metals, oils, greases and soluble organic compounds [161]. Management of this wastewater is a major technical challenge, especially because the polluted waters can continue to backflow from the wells for many years [161]. Numerous instances of groundwater and river contamination have been cited [162]. High levels of methane leakage from fracking have been found [163], as well as nitrogen oxides and volatile organic compounds [159]. Methane leaks increase the climate impact of shale gas, but whether the leaks are sufficient to significantly alter the climate forcing by total natural gas development is uncertain [164]. Overall, environmental and ecologic threats posed by unconven- tional gas extraction are uncertain because of limited research, however evidence for groundwater pollution on both local and river basin scales is a major concern [165]. Today, with cumulative carbon emissions,370 GtC from all fossil fuels, we are at a point of severely escalating ecological and environmental impacts from fossil fuel use and fossil fuel mining, as is apparent from the mountaintop removal for coal, tar sands extraction of oil, and fracking for gas. The ecological and environmental implications of scenarios with carbon emissions of 1000 GtC or greater, as discussed below, would be profound and should influence considerations of appropriate energy strategies. Summary: Climate Impacts Climate impacts accompanying global warming of 2uC or more would be highly deleterious. Already there are numerous indications of substantial effects in response to warming of the past few decades. That warming has brought global temperature close to if not slightly above the prior range of the Holocene. We conclude that an appropriate target would be to keep global temperature at a level within or close to the Holocene range. Global warming of 2uC would be well outside the Holocene range and far into the dangerous range. Transient Climate Change We must quantitatively relate fossil fuel emissions to global temperature in order to assess how rapidly fossil fuel emissions must be phased down to stay under a given temperature limit. Thus we must deal with both a transient carbon cycle and transient global climate change. Global climate fluctuates stochastically and also responds to natural and human-made climate forcings [1,166]. Forcings, measured in W/m 2averaged over the globe, are imposed perturbations of Earth’s energy balance caused by changing forcing agents such as solar irradiance and human-made greenhouse gases (GHGs). CO 2accounts for more than 80% of the added GHG forcing in the past 15 years [64,167] and, if fossil fuel emissions continue at a high level, CO 2will be the dominant driver of future global temperature change. We first define our method of calculating atmospheric CO 2as a function of fossil fuel emissions. We then define our assumptions Assessing Dangerous Climate Change PLOS ONE | www.plosone.org 9 December 2013 | Volume 8 | Issue 12 | e81648 about the potential for drawing down atmospheric CO 2via reforestation and increase of soil carbon, and we define fossil fuel emission reduction scenarios that we employ in our study. Finally we describe all forcings employed in our calculations of global temperature and the method used to simulate global temperature. Carbon Cycle and Atmospheric CO 2 The carbon cycle defines the fate of CO 2injected into the air by fossil fuel burning [1,168] as the additional CO 2distributes itself over time among surface carbon reservoirs: the atmosphere, ocean, soil, and biosphere. We use the dynamic-sink pulse- response function version of the well-tested Bern carbon cycle model [169], as described elsewhere [54,170]. Specifically, we solve equations 3–6, 16–17, A.2.2, and A.3 of Joos et al. [169] using the same parameters and assumptions therein, except that initial (1850) atmospheric CO 2is assumed to be 285.2 ppm [167]. Historical fossil fuel CO 2emissions are from Boden et al. [5]. This Bern model incorporates non-linear ocean chemistry feedbacks and CO 2fertilization of the terrestrial biosphere, but it omits climate-carbon feedbacks, e.g., assuming static global climate and ocean circulation. Therefore our results should be regarded as conservative, especially for scenarios with large emissions. A pulse of CO 2injected into the air decays by half in about 25 years as CO 2is taken up by the ocean, biosphere and soil, but nearly one-fifth is still in the atmosphere after 500 years (Fig. 4A). Eventually, over hundreds of millennia, weathering of rocks will deposit all of this initial CO 2pulse on the ocean floor as carbonate sediments [168]. Under equilibrium conditions a negative CO 2pulse, i.e., artificial extraction and storage of some CO 2amount, decays at about the same rate as a positive pulse (Fig. 4A). Thus if it is decided in the future that CO 2must be extracted from the air and removed from the carbon cycle (e.g., by storing it underground or in carbonate bricks), the impact on atmospheric CO 2amount will diminish in time. This occurs because carbon is exchanged among the surface carbon reservoirs as they move toward an equilibrium distribution, and thus, e.g., CO 2out-gassing by the ocean can offset some of the artificial drawdown. The CO 2extraction required to reach a given target atmospheric CO 2level therefore depends on the prior emission history and target timeframe, but the amount that must be extracted substantially exceeds the net reduction of the atmospheric CO 2level that will be achieved. We clarify this matter below by means of specific scenarios for capture of CO 2. It is instructive to see how fast atmospheric CO 2declines if fossil fuel emissions are instantly terminated (Fig. 4B). Halting emissions in 2015 causes CO 2to decline to 350 ppm at century’s end (Fig. 4B). A 20 year delay in halting emissions has CO 2returning to 350 ppm at about 2300. With a 40 year delay, CO 2does not return to 350 ppm until after 3000. These results show how difficult it is to get back to 350 ppm if emissions continue to grow for even a few decades. These results emphasize the urgency of initiating emissions reduction[171]. As discussed above, keeping global climate close to the Holocene range requires a long-term atmospheric CO 2level of about 350 ppm or less, with other climate forcings similar to today’s levels. If emissions reduction had begun in 2005, reduction at 3.5%/year would have achieved 350 ppm at 2100. Now the requirement is at least 6%/year. Delay of emissions reductions until 2020 requires a reduction rate of 15%/year to achieve 350 ppm in 2100. If we assume only 50 GtC reforestation, and begin emissions reduction in 2013, the required reduction rate becomes about 9%/year. Reforestation and Soil Carbon Of course fossil fuel emissions will not suddenly terminate. Nevertheless, it is not impossible to return CO 2to 350 ppm this century. Reforestation and increase of soil carbon can help draw down atmospheric CO 2. Fossil fuels account for,80% of the CO 2 increase from preindustrial time, with land use/deforestation accounting for 20% [1,170,172–173]. Net deforestation to date is estimated to be 100 GtC (gigatons of carbon) with650% uncertainty [172]. Complete restoration of deforested areas is unrealistic, yet 100 GtC carbon drawdown is conceivable because: (1) the human- enhanced atmospheric CO 2level increases carbon uptake by some vegetation and soils, (2) improved agricultural practices can convert agriculture from a CO 2ource into a CO 2sink [174], (3) biomass-burning power plants with CO 2capture and storage can contribute to CO 2drawdown. Forest and soil storage of 100 GtC is challenging, but has other benefits. Reforestation has been successful in diverse places [175]. Minimum tillage with biological nutrient recycling, as opposed to plowing and chemical fertilizers, could sequester 0.4–1.2 GtC/year [176] while conserving water in soils, building agricultural resilience to climate change, and increasing productivity especially in smallholder rain-fed agriculture, thereby reducing expansion of agriculture into forested ecosystems [177–178]. Net tropical defor- estation may have decreased in the past decade [179], but because of extensive deforestation in earlier decades [170,172–173,180–181] there is a large amount of land suitable for reforestation [182]. Use of bioenergy to draw down CO 2should employ feedstocks from residues, wastes, and dedicated energy crops that do not compete with food crops, thus avoiding loss of natural ecosystems and cropland [183–185]. Reforestation competes with agricultural land use; land needs could decline by reducing use of animal products, as livestock now consume more than half of all crops [186]. Our reforestation scenarios assume that today’s net deforesta- tion rate (,1 GtC/year; see [54]) will stay constant until 2020, then linearly decrease to zero by 2030, followed by sinusoidal 100 GtC biospheric carbon storage over 2031–2080. Alternative timings do not alter conclusions about the potential to achieve a given CO 2level such as 350 ppm. Emission Reduction Scenarios A 6%/year decrease of fossil fuel emissions beginning in 2013, with 100 GtC reforestation, achieves a CO 2decline to 350 ppm near the end of this century (Fig. 5A). Cumulative fossil fuel emissions in this scenario are,129 GtC from 2013 to 2050, with an additional 14 GtC by 2100. If our assumed land use changes occur a decade earlier, CO 2returns to 350 ppm several years earlier; however that has negligible effect on the maximum global temperature calculated below. Delaying fossil fuel emission cuts until 2020 (with 2%/year emissions growth in 2012–2020) causes CO 2to remain above 350 ppm (with associated impacts on climate) until 2300 (Fig. 5B). If reductions are delayed until 2030 or 2050, CO 2remains above 350 ppm or 400 ppm, respectively, until well after 2500. We conclude that it is urgent that large, long-term emission reductions begin soon. Even if a 6%/year reduction rate and 500 GtC are not achieved, it makes a huge difference when reductions begin. There is no practical justification for why emissions necessarily must even approach 1000 GtC. Climate Forcings Atmospheric CO 2and other GHGs have been well-measured for the past half century, allowing accurate calculation of their climate forcing. The growth rate of the GHG forcing has declined Assessing Dangerous Climate Change PLOS ONE | www.plosone.org 10 December 2013 | Volume 8 | Issue 12 | e81648 moderately since its peak values in the 1980s, as the growth rate of CH 4and chlorofluorocarbons has slowed [187]. Annual changes of CO 2are highly correlated with the El Nin˜ o cycle (Fig. 6). Two strong La Nin˜ as in the past five years have depressed CO 2growth as well as the global warming rate (Fig. 3). The CO 2growth rate and warming rate can be expected to increase as we move into the next El Nin˜ o, with the CO 2growth already reaching 3 ppm/year in mid-2013 [188]. The CO 2climate forcing does not increase as rapidly as the CO 2amount because of partial saturation of CO 2 absorption bands [75]. The GHG forcing is now increasing at a rate of almost 0.4 W/m 2per decade [187]. Solar irradiance variations are sometimes assumed to be the most likely natural driver of climate change. Solar irradiance has been measured from satellites since the late 1970s (Fig. 7). These data are from a composite of several satellite-measured time series. Data through 28 February 2003 are from [189] and Physikalisch Meteorologisches Observatorium Davos, World Radiation Center. Subsequent update is from University of Colorado Solar Radiation & Climate Experiment (SORCE). Data sets are concatenated by matching the means over the first 12 months of SORCE data. Monthly sunspot numbers (Fig. 7) support the conclusion that the solar irradiance in the current solar cycle is significantly lower than in the three preceding solar cycles. Amplification of the direct solar forcing is conceivable, e.g., through effects on ozone or atmospheric condensation nuclei, but empirical data place a factor of two upper limit on the amplification, with the most likely forcing in the range 100–120% of the directly measured solar irradiance change [64]. Recent reduced solar irradiance (Fig. 7) may have decreased the forcing over the past decade by about half of the full amplitude of measured irradiance variability, thus yielding a negative forcing of, say,20.12 W/m 2. This compares with a decadal increase of the GHG forcing that is positive and about three times larger in magnitude. Thus the solar forcing is not negligible and might partially account for the slowdown in global warming in the past decade [17]. However, we must (1) compare the solar forcing withthe net of other forcings, which enhances the importance of solar change, because the net forcing is smaller than the GHG forcing, and (2) consider forcing changes on longer time scales, which greatly diminishes the importance of solar change, because solar variability is mainly oscillatory. Human-made tropospheric aerosols, which arise largely from fossil fuel use, cause a substantial negative forcing. As noted above, two independent analyses [64,72] yield a total (direct plus indirect) aerosol forcing in the past decade of about21.5 W/m 2, half the magnitude of the GHG forcing and opposite in sign. That empirical aerosol forcing assessment for the past decade is consistent with the climate forcings scenario (Fig. 8) that we use for the past century in the present and prior studies [64,190]. Supplementary Table S1 specifies the historical forcings and Table S2 gives several scenarios for future forcings. Future Climate Forcings Future global temperature change should depend mainly on atmospheric CO 2, at least if fossil fuel emissions remain high. Thus to provide the clearest picture of the CO 2effect, we approximate the net future change of human-made non-CO 2forcings as zero and we exclude future changes of natural climate forcings, such as solar irradiance and volcanic aerosols. Here we discuss possible effects of these approximations. Uncertainties in non-CO 2forcings concern principally solar, aerosol and other GHG forcings. Judging from the sunspot numbers (Fig. 7B and [191]) for the past four centuries, the current solar cycle is almost as weak as the Dalton Minimum of the late 18th century. Conceivably irradiance could decline further to the level of the Maunder Minimum of the late 17th century [192– 193]. For our simulation we choose an intermediate path between recovery to the level before the current solar cycle and decline to a still lower level. Specifically, we keep solar irradiance fixed at the reduced level of 2010, which is probably not too far off in either direction. Irradiance in 2010 is about 0.1 W/m 2less than the mean of the prior three solar cycles, a decrease of forcing that Figure 6. Annual increase of CO 2based on data from the NOAA Earth System Research Laboratory[188].Prior to 1981 the CO 2change is based on only Mauna Loa, Hawaii. Temperature changes in lower diagram are 12-month running means for the globe and Nin˜ o3.4 area [16]. doi:10.1371/journal.pone.0081648.g006Assessing Dangerous Climate Change PLOS ONE | www.plosone.org 11 December 2013 | Volume 8 | Issue 12 | e81648 would be restored by the CO 2increase within 3–4 years at its current growth rate. Extensive simulations [17,194] confirm that the effect of solar variability is small compared with GHGs if CO 2 emissions continue at a high level. However, solar forcing can affect the magnitude and detection of near-term warming. Also, if rapidly declining GHG emissions are achieved, changes of solar forcing will become relatively more important. Aerosols present a larger uncertainty. Expectations of decreases in large source regions such as China [195] may be counteracted by aerosol increases other places as global population continues to increase. Our assumption of unchanging human-made aerosols could be substantially off in either direction. For the sake of interpreting on-going and future climate change it is highly desirable to obtain precise monitoring of the global aerosol forcing [73].Non-CO 2GHG forcing has continued to increase at a slow rate since 1995 (Fig. 6 in [64]). A desire to constrain climate change may help reduce emissions of these gases in the future. However, it will be difficult to prevent or fully offset positive forcing from increasing N 2O, as its largest source is associated with food production and the world’s population is continuing to rise. On the other hand, we are also probably underestimating a negative aerosol forcing, e.g., because we have not included future volcanic aerosols. Given the absence of large volcanic eruptions in the past two decades (the last one being Mount Pinatubo in 1991), multiple volcanic eruptions would cause a cooling tendency [196] and reduce heat storage in the ocean [197]. Overall, we expect the errors due to our simple approximation of non-CO 2forcings to be partially off-setting. Specifically, we have likely underestimated a positive forcing by non-CO 2GHGs, while also likely underestimating a negative aerosol forcing. Figure 7. Solar irradiance and sunspot number in the era of satellite data (see text).Left scale is the energy passing through an area perpendicular to Sun-Earth line. Averaged over Earth’s surface the absorbed solar energy is,240 W/m 2, so the full amplitude of measured solar variability is,0.25 W/m 2. doi:10.1371/journal.pone.0081648.g007 Figure 8. Climate forcings employed in our six main scenarios.Forcings through 2010 are as in [64]. doi:10.1371/journal.pone.0081648.g008Assessing Dangerous Climate Change PLOS ONE | www.plosone.org 12 December 2013 | Volume 8 | Issue 12 | e81648 Note that uncertainty in forcings is partly obviated via the focus on Earth’s energy imbalance in our analysis. The planet’s energy imbalance is an integrative quantity that is especially useful for a case in which some of the forcings are uncertain or unmeasured. Earth’s measured energy imbalance includes the effects of all forcings, whether they are measured or not. Simulations of Future Global Temperature We calculate global temperature change for a given CO 2 scenario using a climate response function (Table S3) that accurately replicates results from a global climate model with sensitivity 3uC for doubled CO 2[64]. A best estimate of climate sensitivity close to 3uC for doubled CO 2has been inferred from paleoclimate data [51–52]. This empirical climate sensitivity is generally consistent with that of global climate models [1], but the empirical approach makes the inferred high sensitivity more certain and the quantitative evaluation more precise. Because this climate sensitivity is derived from empirical data on how Earth responded to past changes of boundary conditions, including atmospheric composition, our conclusions about limits on fossil fuel emissions can be regarded as largely independent of climate models. The detailed temporal and geographical response of the climate system to the rapid human-made change of climate forcings is not well-constrained by empirical data, because there is no faithful paleoclimate analog. Thus climate models necessarily play an important role in assessing practical implications of climate change. Nevertheless, it is possible to draw important conclusions with transparent computations. A simple response function (Green’s function) calculation [64] yields an estimate of global mean temperature change in response to a specified time series for global climate forcing. This approach accounts for the delayed response of the climate system caused by the large thermal inertia of the ocean, yielding a global mean temporal response in close accord with that obtained from global climate models. Tables S1 and S2 in Supporting Information give the forcings we employ and Table S3 gives the climate response function for our Green’s function calculation, defined by equation 2 of [64]. The Green’s function is driven by the net forcing, which, with the response function, is sufficient information for our results to be reproduced. However, we also include the individual forcings in Table S1, in case researchers wish to replace specific forcings or use them for other purposes. Simulated global temperature (Fig. 9) is for CO 2scenarios of Fig. 5. Peak global warming is,1.1uC, declining to less than 1uC by mid-century, if CO 2emissions are reduced 6%/year beginning in 2013. In contrast, warming reaches 1.5uC and stays above 1uC until after 2400 if emissions continue to increase until 2030, even though fossil fuel emissions are phased out rapidly (5%/year) after 2030 and 100 GtC reforestation occurs during 2030–2080. If emissions continue to increase until 2050, simulated warming exceeds 2uC well into the 22 nd century. Increased global temperature persists for many centuries after the climate forcing declines, because of the thermal inertia of the ocean [198]. Some temperature reduction is possible if the climate forcing is reduced rapidly, before heat has penetrated into the deeper ocean. Cooling by a few tenths of a degree in Fig. 9 is a result mainly of the 100 GtC biospheric uptake of CO 2during 2030–2080. Note the longevity of the warming, especially if emissions reduction is as slow as 2%/year, which might be considered to be a rapid rate of reduction. The temporal response of the real world to the human-made climate forcing could be more complex than suggested by a simple response function calculation, especially if rapid emissions growthcontinues, yielding an unprecedented climate forcing scenario. For example, if ice sheet mass loss becomes rapid, it is conceivable that the cold fresh water added to the ocean could cause regional surface cooling [199], perhaps even at a point when sea level rise has only reached a level of the order of a meter [200]. However, any uncertainty in the surface thermal response this century due to such phenomena has little effect on our estimate of the dangerous level of emissions. The long lifetime of the fossil fuel carbon in the climate system and the persistence of ocean warming for millennia [201] provide sufficient time for the climate system to achieve full response to the fast feedback processes included in the 3uC climate sensitivity. Indeed, the long lifetime of fossil fuel carbon in the climate system and persistence of the ocean warming ensure that ‘‘slow’’ feedbacks, such as ice sheet disintegration, changes of the global vegetation distribution, melting of permafrost, and possible release of methane from methane hydrates on continental shelves, would also have time to come into play. Given the unprecedented rapidity of the human-made climate forcing, it is difficult to establish how soon slow feedbacks will become important, but clearly slow feedbacks should be considered in assessing the ‘‘dangerous’’ level of global warming, as discussed in the next section. Danger of Initiating Uncontrollable Climate Change Our calculated global warming as a function of CO 2amount is based on equilibrium climate sensitivity 3uC for doubled CO 2. That is the central climate sensitivity estimate from climate models [1], and it is consistent with climate sensitivity inferred from Earth’s climate history [51–52]. However, this climate sensitivity includes only the effects of fast feedbacks of the climate system, such as water vapor, clouds, aerosols, and sea ice. Slow feedbacks, such as change of ice sheet area and climate-driven changes of greenhouse gases, are not included. Slow Climate Feedbacks and Irreversible Climate Change Excluding slow feedbacks was appropriate for simulations of the past century, because we know the ice sheets were stable then and our climate simulations used observed greenhouse gas amounts that included any contribution from slow feedbacks. However, we must include slow feedbacks in projections of warming for the 21 st century and beyond. Slow feedbacks are important because they affect climate sensitivity and because their instigation is related to the danger of passing ‘‘points of no return’’, beyond which irreversible consequences become inevitable, out of humanity’s control. Antarctic and Greenland ice sheets present the danger of change with consequences that are irreversible on time scales important to society [1]. These ice sheets required millennia to grow to their present sizes. If ice sheet disintegration reaches a point such that the dynamics and momentum of the process take over, at that point reducing greenhouse gases may be unable to prevent major ice sheet mass loss, sea level rise of many meters, and worldwide loss of coastal cities – a consequence that is irreversible for practical purposes. Interactions between the ocean and ice sheets are particularly important in determining ice sheet changes, as a warming ocean can melt the ice shelves, the tongues of ice that extend from the ice sheets into the ocean and buttress the large land-based ice sheets [92,202–203]. Paleoclimate data for sea level change indicate that sea level changed at rates of the order of a meter per century [81–83], even at times when the forcings driving climate change were far weaker than the human- Assessing Dangerous Climate Change PLOS ONE | www.plosone.org 13 December 2013 | Volume 8 | Issue 12 | e81648 made forcing. Thus, because ocean warming is persistent for centuries, there is a danger that large irreversible change could be initiated by excessive ocean warming. Paleoclimate data are not as helpful for defining the likely rate of sea level rise in coming decades, because there is no known case of growth of a positive (warming) climate forcing as rapid as the anthropogenic change. The potential for unstable ice sheet disintegration is controversial, with opinion varying from likely stability of even the (marine) West Antarctic ice sheet [94] to likely rapid non-linear response extending up to multi-meter sea level rise [97–98]. Data for the modern rate of annual ice sheet mass changes indicate an accelerating rate of mass loss consistent with a mass loss doubling time of a decade or less (Fig. 10). However, we do not know the functional form of ice sheet response to a large persistent climate forcing. Longer records are needed for empirical assessment of this ostensibly nonlinear behavior. Greenhouse gas amounts in the atmosphere, most importantly CO 2and CH 4, change in response to climate change, i.e., as a feedback, in addition to the immediate gas changes from human- caused emissions. As the ocean warms, for example, it releases CO 2to the atmosphere, with one principal mechanism being the simple fact that the solubility of CO 2decreases as the water temperature rises [204]. We also include in the category of slow feedbacks the global warming spikes, or ‘‘hyperthermals’’, that have occurred a number of times in Earth’s history during the course of slower global warming trends. The mechanisms behindthese hyperthermals are poorly understood, as discussed below, but they are characterized by the injection into the surface climate system of a large amount of carbon in the form of CH 4and/or CO 2on the time scale of a millennium [205–207]. The average rate of injection of carbon into the climate system during these hyperthermals was slower than the present human-made injection of fossil fuel carbon, yet it was faster than the time scale for removal of carbon from the surface reservoirs via the weathering process [3,208], which is tens to hundreds of thousands of years. Methane hydrates – methane molecules trapped in frozen water molecule cages in tundra and on continental shelves – and organic matter such as peat locked in frozen soils (permafrost) are likely mechanisms in the past hyperthermals, and they provide another climate feedback with the potential to amplify global warming if large scale thawing occurs [209–210]. Paleoclimate data reveal instances of rapid global warming, as much as 5–6uC, as a sudden additional warming spike during a longer period of gradual warming [see Text S1]. The candidates for the carbon injected into the climate system during those warmings are methane hydrates on continental shelves destabilized by sea floor warming [211] and carbon released from frozen soils [212]. As for the present, there are reports of methane release from thawing permafrost on land [213] and from sea-bed methane hydrate deposits [214], but amounts so far are small and the data are snapshots that do not prove that there is as yet a temporal increase of emissions. Figure 9. Simulated global temperature relative to 1880–1920 mean for CO 2scenarios of Figure 5. doi:10.1371/journal.pone.0081648.g009 Figure 10. Annual Greenland and West Antarctic ice mass changes as estimated via alternative methods.Data were read from Figure 4 of Shepherd et al. [23] and averaged over the available records. doi:10.1371/journal.pone.0081648.g010Assessing Dangerous Climate Change PLOS ONE | www.plosone.org 14 December 2013 | Volume 8 | Issue 12 | e81648 There is a possibility of rapid methane hydrate or permafrost emissions in response to warming, but that risk is largely unquantified [215]. The time needed to destabilize large methane hydrate deposits in deep sediments is likely millennia [215]. Smaller but still large methane hydrate amounts below shallow waters as in the Arctic Ocean are more vulnerable; the methane may oxidize to CO 2in the water, but it will still add to the long- term burden of CO 2in the carbon cycle. Terrestrial permafrost emissions of CH 4and CO 2likely can occur on a time scale of a few decades to several centuries if global warming continues [215]. These time scales are within the lifetime of anthropogenic CO 2, and thus these feedbacks must be considered in estimating the dangerous level of global warming. Because human-made warming is more rapid than natural long-term warmings in the past, there is concern that methane hydrate or peat feedbacks could be more rapid than the feedbacks that exist in the paleoclimate record. Climate model studies and empirical analyses of paleoclimate data can provide estimates of the amplification of climate sensitivity caused by slow feedbacks, excluding the singular mechanisms that caused the hyperthermal events. Model studies for climate change between the Holocene and the Pliocene, when Earth was about 3uC warmer, find that slow feedbacks due to changes of ice sheets and vegetation cover amplified the fast feedback climate response by 30–50% [216]. These same slow feedbacks are estimated to amplify climate sensitivity by almost a factor of two for the climate change between the Holocene and the nearly ice-free climate state that existed 35 million years ago [54]. Implication for Carbon Emissions Target Evidence presented under Climate Impacts above makes clear that 2uC global warming would have consequences that can be described as disastrous. Multiple studies [12,198,201] show that the warming would be very long lasting. The paleoclimate record and changes underway in the Arctic and on the Greenland and Antarctic ice sheets with only today’s warming imply that sea level rise of several meters could be expected. Increased climate extremes, already apparent at 0.8uC warming [46], would be more severe. Coral reefs and associated species, already stressed with current conditions [40], would be decimated by increased acidification, temperature and sea level rise. More generally, humanity and nature, the modern world as we know it, is adapted to the Holocene climate that has existed more than 10,000 years. Warming of 1uC relative to 1880–1920 keeps global temperature close to the Holocene range, but warming of 2uC, to at least the Eemian level, could cause major dislocations for civilization. However, distinctions between pathways aimed at,1uC and 2uC warming are much greater and more fundamental than the numbers 1uC and 2uC themselves might suggest. These funda- mental distinctions make scenarios with 2uC or more global warming far more dangerous; so dangerous, we suggest, that aiming for the 2uC pathway would be foolhardy. First, most climate simulations, including ours above and those of IPCC [1], do not include slow feedbacks such as reduction of ice sheet size with global warming or release of greenhouse gases from thawing tundra. These exclusions are reasonable for a,1uC scenario, because global temperature barely rises out of the Holocene range and then begins to subside. In contrast, global warming of 2uC or more is likely to bring slow feedbacks into play. Indeed, it is slow feedbacks that cause long-term climate sensitivity to be high in the empirical paleoclimate record [51–52]. The lifetime of fossil fuel CO 2in the climate system is so long that it must be assumed that these slow feedbacks will occur if temperature rises well above the Holocene range.Second, scenarios with 2uC or more warming necessarily imply expansion of fossil fuels into sources that are harder to get at, requiring greater energy using extraction techniques that are increasingly invasive, destructive and polluting. Fossil fuel emissions through 2012 total,370 GtC (Fig. 2). If subsequent emissions decrease 6%/year, additional emissions are,130 GtC, for a total,500 GtC fossil fuel emissions. This 130 GtC can be obtained mainly from the easily extracted conventional oil and gas reserves (Fig. 2), with coal use rapidly phased out and unconven- tional fossil fuels left in the ground. In contrast, 2uC scenarios have total emissions of the order of 1000 GtC. The required additional fossil fuels will involve exploitation of tar sands, tar shale, hydrofracking for oil and gas, coal mining, drilling in the Arctic, Amazon, deep ocean, and other remote regions, and possibly exploitation of methane hydrates. Thus 2uC scenarios result in more CO 2per unit useable energy, release of substantial CH 4via the mining process and gas transportation, and release of CO 2and other gases via destruction of forest ‘‘overburden’’ to extract subterranean fossil fuels. Third, with our,1uC scenario it is more likely that the biosphere and soil will be able to sequester a substantial portion of the anthropogenic fossil fuel CO 2carbon than in the case of 2uC or more global warming. Empirical data for the CO 2‘‘airborne fraction’’, the ratio of observed atmospheric CO 2increase divided by fossil fuel CO 2emissions, show that almost half of the emissions is being taken up by surface (terrestrial and ocean) carbon reservoirs [187], despite a substantial but poorly measured contribution of anthropogenic land use (deforestation and agriculture) to airborne CO 2[179,216]. Indeed, uptake of CO 2 by surface reservoirs has at least kept pace with the rapid growth of emissions [187]. Increased uptake in the past decade may be a consequence of a reduced rate of deforestation [217] and fertilization of the biosphere by atmospheric CO 2and nitrogen deposition [187]. With the stable climate of the,1uC scenario it is plausible that major efforts in reforestation and improved agricultural practices [15,173,175–177], with appropriate support provided to developing countries, could take up an amount of carbon comparable to the 100 GtC in our,1uC scenario. On the other hand, with warming of 2uC or more, carbon cycle feedbacks are expected to lead to substantial additional atmospheric CO 2 [218–219], perhaps even making the Amazon rainforest a source of CO 2[219–220]. Fourth, a scenario that slows and then reverses global warming makes it possible to reduce other greenhouse gases by reducing their sources [75,221]. The most important of these gases is CH 4, whose reduction in turn reduces tropospheric O 3and stratospheric H 2O. In contrast, chemistry modeling and paleoclimate records [222] show that trace gases increase with global warming, making it unlikely that overall atmospheric CH 4will decrease even if a decrease is achieved in anthropogenic CH 4sources. Reduction of the amount of atmospheric CH 4and related gases is needed to counterbalance expected forcing from increasing N 2O and decreasing sulfate aerosols. Now let us compare the 1uC (500 GtC fossil fuel emissions) and the 2uC (1000 GtC fossil fuel emissions) scenarios. Global temperature in 2100 would be close to 1uC in the 500 GtC scenario, and it is less than 1uC if 100 GtC uptake of carbon by the biosphere and soil is achieved via improved agricultural and forestry practices (Fig. 9). In contrast, the 1000 GtC scenario, although nominally designed to yield a fast-feedback climate response of,2uC, would yield a larger eventual warming because of slow feedbacks, probably at least 3uC. Assessing Dangerous Climate Change PLOS ONE | www.plosone.org 15 December 2013 | Volume 8 | Issue 12 | e81648 Danger of Uncontrollable Consequences Inertia of the climate system reduces the near-term impact of human-made climate forcings, but that inertia is not necessarily our friend. One implication of the inertia is that climate impacts ‘‘in the pipeline’’ may be much greater than the impacts that we presently observe. Slow climate feedbacks add further danger of climate change running out of humanity’s control. The response time of these slow feedbacks is uncertain, but there is evidence that some of these feedbacks already are underway, at least to a minor degree. Paleoclimate data show that on century and millennial time scales the slow feedbacks are predominately amplifying feedbacks. The inertia of energy system infrastructure, i.e., the time required to replace fossil fuel energy systems, will make it exceedingly difficult to avoid a level of atmospheric CO 2that would eventually have highly undesirable consequences. The danger of uncontrollable and irreversible consequences necessarily raises the question of whether it is feasible to extract CO 2from the atmosphere on a large enough scale to affect climate change. Carbon Extraction We have shown that extraordinarily rapid emission reductions are needed to stay close to the 1uC scenario. In absence of extraordinary actions, it is likely that growing climate disruptions will lead to a surge of interest in ‘‘geo-engineering’’ designed to minimize human-made climate change [223]. Such efforts must remove atmospheric CO 2, if they are to address direct CO 2effects such as ocean acidification as well as climate change. Schemes such as adding sulfuric acid aerosols to the stratosphere to reflect sunlight [224], an attempt to mask one pollutant with another, is a temporary band-aid for a problem that will last for millennia; besides it fails to address ocean acidification and may have other unintended consequences [225]. Potential for Carbon Extraction At present there are no proven technologies capable of large- scale air capture of CO 2. It has been suggested that, with strong research and development support and industrial scale pilot projects sustained over decades, costs as low as, $500/tC may be achievable [226]. Thermodynamic constraints [227] suggest that this cost estimate may be low. An assessment by the American Physical Society [228] argues that the lowest currently achievable cost, using existing approaches, is much greater ( $600/tCO 2or $2200/tC). The cost of capturing 50 ppm of CO 2,at $500/tC (, $135/ tCO 2), is, $50 trillion (1 ppm CO 2is,2.12 GtC), but more than $200 trillion for the price estimate of the American Physical Society study. Moreover, the resulting atmospheric CO 2reduction will ultimately be less than 50 ppm for the reasons discussed above. For example, let us consider the scenario of Fig. 5B in which emissions continue to increase until 2030 before decreasing at 5%/year – this scenario yields atmospheric CO 2of 410 ppm in 2100. Using our carbon cycle model we calculate that if we extract 100 ppm of CO 2from the air over the period 2030–2100 (10/7 ppm per year), say storing that CO 2in carbonate bricks, the atmospheric CO 2amount in 2100 will be reduced 52 ppm to 358 ppm, i.e., the reduction of airborne CO 2is about half of the amount extracted from the air and stored. The estimated cost of this 52 ppm CO 2reduction is $100–400 trillion. The cost of CO 2capture and storage conceivably may decline in the future. Yet the practicality of carrying out such a program with alacrity in response to a climate emergency is dubious. Thus it may be appropriate to add a CO 2removal cost to the currentprice of fossil fuels, which would both reduce ongoing emissions and provide resources for future cleanup. Responsibility for Carbon Extraction We focus on fossil fuel carbon, because of its long lifetime in the carbon cycle. Reversing the effects of deforestation is also important and there will need to be incentives to achieve increased carbon storage in the biosphere and soil, but the crucial requirement now is to limit the amount of fossil fuel carbon in the air. The high cost of carbon extraction naturally raises the question of responsibility for excess fossil fuel CO 2in the air. China has the largest CO 2emissions today (Fig. 11A), but the global warming effect is closely proportional to cumulative emissions [190]. The United States is responsible for about one-quarter of cumulative emissions, with China next at about 10% (Fig. 11B). Cumulative responsibilities change rather slowly (compare Fig. 10 of 190). Estimated per capita emissions (Fig. 12) are based on population estimates for 2009–2011. Various formulae might be devised to assign costs of CO 2air capture, should removal prove essential for maintaining acceptable climate. For the sake of estimating the potential cost, let us assume that it proves necessary to extract 100 ppm of CO 2(yielding a reduction of airborne CO 2of about 50 ppm) and let us assign each country the responsibility to clean up its fraction of cumulative emissions. Assuming a cost of $500/tC (, $135/tCO 2) yields a cost of $28 trillion for the United States, about $90,000 per individual. Costs would be slightly higher for a UK citizen, but less for other nations (Fig. 12B). Cost of CO 2capture might decline, but the cost estimate used is more than a factor of four smaller than estimated by the American Physical Society [228] and 50 ppm is only a moderate reduction. The cost should also include safe permanent disposal of the captured CO 2, which is a substantial mass. For the sake of scaling the task, note that one GtC, made into carbonate bricks, would produce the volume of,3000 Empire State buildings or,1200 Great Pyramids of Giza. Thus the 26 ppm assigned to the United States, if made into carbonate bricks, would be equivalent to the stone in 165,000 Empire State buildings or 66,000 Great Pyramids of Giza. This is not intended as a practical suggestion: carbonate bricks are not a good building material, and the transport and construction costs would be additional. The point of this graphic detail is to make clear the magnitude of the cleanup task and potential costs, if fossil fuel emissions continue unabated. More useful and economic ways of removing CO 2may be devised with the incentive of a sufficient carbon price. For example, a stream of pure CO 2becomes available for capture and storage if biomass is used as the fuel for power plants or as feedstock for production of liquid hydrocarbon fuels. Such clean energy schemes and improved agricultural and forestry practices are likely to be more economic than direct air capture of CO 2, but they must be carefully designed to minimize undesirable impacts and the amount of CO 2that can be extracted on the time scale of decades will be limited, thus emphasizing the need to limit the magnitude of the cleanup task. Policy Implications Human-made climate change concerns physical sciences, but leads to implications for policy and politics. Conclusions from the physical sciences, such as the rapidity with which emissions must be reduced to avoid obviously unacceptable consequences and the long lag between emissions and consequences, lead to implications in social sciences, including economics, law and ethics. Intergov- Assessing Dangerous Climate Change PLOS ONE | www.plosone.org 16 December 2013 | Volume 8 | Issue 12 | e81648 ernmental climate assessments [1,14] purposely are not policy prescriptive. Yet there is also merit in analysis and discussion of the full topic through the objective lens of science, i.e., ‘‘connecting the dots’’ all the way to policy implications. Energy and Carbon Pathways: A Fork in the Road The industrial revolution began with wood being replaced by coal as the primary energy source. Coal provided more concentrated energy, and thus was more mobile and effective. We show data for the United States (Fig. 13) because of the availability of a long data record that includes wood [229]. More limited global records yield a similar picture [Fig. 14], the largest difference being global coal now at,30% compared with,20% in the United States. Economic progress and wealth generation were further spurred in the twentieth century by expansion into liquid and gaseous fossil fuels, oil and gas being transported and burned more readily than coal. Only in the latter part of the twentieth century did it become clear that long-lived combustion products from fossil fuels posed a global climate threat, as formally acknowledged in the 1992 Framework Convention on Climate Change [6]. However, efforts to slow emissions of the principalatmospheric gas driving climate change, CO 2, have been ineffectual so far (Fig. 1). Consequently, at present, as the most easily extracted oil and gas reserves are being depleted, we stand at a fork in the road to our energy and carbon future. Will we now feed our energy needs by pursuing difficult to extract fossil fuels, or will we pursue energy policies that phase out carbon emissions, moving on to the post fossil fuel era as rapidly as practical? This is not the first fork encountered. Most nations agreed to the Framework Convention on Climate Change in 1992 [6]. Imagine if a bloc of countries favoring action had agreed on a common gradually rising carbon fee collected within each of country at domestic mines and ports of entry. Such nations might place equivalent border duties on products from nations not having a carbon fee and they could rebate fees to their domestic industry for export products to nations without an equivalent carbon fee. The legality of such a border tax adjustment under international trade law is untested, but is considered to be plausibly consistent with trade principles [230]. As the carbon fee gradually rose and as additional nations, for their own benefit, joined this bloc of nations, development of carbon-free energies and energy efficiency would have been spurred. If the carbon fee had begun in 1995, we Figure 11. Fossil fuel CO 2emissions.(A) 2012 emissions by source region, and (B) cumulative 1751–2012 emissions. Results are an update of Fig. 10 of [190] using data from [5]. doi:10.1371/journal.pone.0081648.g011 Figure 12. Per capita fossil fuel CO 2emissions.Countries, regions and data sources are the same as in Fig. 11. Horizontal lines are the global mean and multiples of the global mean. doi:10.1371/journal.pone.0081648.g012Assessing Dangerous Climate Change PLOS ONE | www.plosone.org 17 December 2013 | Volume 8 | Issue 12 | e81648 calculate that global emissions would have needed to decline 2.1%/year to limit cumulative fossil fuel emissions to 500 GtC. A start date of 2005 would have required a reduction of 3.5%/year for the same result. The task faced today is more difficult. Emissions reduction of 6%/year and 100 GtC storage in the biosphere and soils are needed to get CO 2back to 350 ppm, the approximate require- ment for restoring the planet’s energy balance and stabilizing climate this century. Such a pathway is exceedingly difficult to achieve, given the current widespread absence of policies to drive rapid movement to carbon-free energies and the lifetime of energy infrastructure in place. Yet we suggest that a pathway is still conceivable that could restore planetary energy balance on the century time scale. That path requires policies that spur technology development and provide economic incentives for consumers and businesses such that social tipping points are reached where consumers move rapidly to energy conservation and low carbon energies. Moderate overshoot of required atmospheric CO 2levels can possibly be counteracted via incentives for actions that more-or-less naturally sequester carbon. Developed countries, responsible for most of the excess CO 2in the air, might finance extensive efforts in developing countries to sequester carbon in the soil and in forest regrowth on marginal lands as described above. Burning sustainably designedbiofuels in power plants, with the CO 2captured and sequestered, would also help draw down atmospheric CO 2. This pathway would need to be taken soon, as the magnitude of such carbon extractions is likely limited and thus not a solution to unfettered fossil fuel use. The alternative pathway, which the world seems to be on now, is continued extraction of all fossil fuels, including development of unconventional fossil fuels such as tar sands, tar shale, hydro- fracking to extract oil and gas, and exploitation of methane hydrates. If that path (with 2%/year growth) continues for 20 years and is then followed by 3%/year emission reduction from 2033 to 2150, we find that fossil fuel emissions in 2150 would total 1022 GtC. Extraction of the excess CO 2from the air in this case would be very expensive and perhaps implausible, and warming of the ocean and resulting climate impacts would be practically irreversible. Economic Implications: Need for a Carbon Fee The implication is that the world must move rapidly to carbon- free energies and energy efficiency, leaving most remaining fossil fuels in the ground, if climate is to be kept close to the Holocene range and climate disasters averted. Is rapid change possible? Figure 13. United States energy consumption[229]. doi:10.1371/journal.pone.0081648.g013 Figure 14. World energy consumption for indicated fuels, which excludes wood[4]. doi:10.1371/journal.pone.0081648.g014Assessing Dangerous Climate Change PLOS ONE | www.plosone.org 18 December 2013 | Volume 8 | Issue 12 | e81648 The potential for rapid change can be shown by examples. A basic requirement for phasing down fossil fuel emissions is abundant carbon-free electricity, which is the most rapidly growing form of energy and also has the potential to provide energy for transportation and heating of buildings. In one decade (1977–1987), France increased its nuclear power production 15- fold, with the nuclear portion of its electricity increasing from 8% to 70% [231]. In one decade (2001–2011) Germany increased the non-hydroelectric renewable energy portion of its electricity from 4% to 19%, with fossil fuels decreasing from 63% to 61% (hydroelectric decreased from 4% to 3% and nuclear power decreased from 29% to 18%) [231]. Given the huge task of replacing fossil fuels, contributions are surely required from energy efficiency, renewable energies, and nuclear power, with the mix depending on local preferences. Renewable energy and nuclear power have been limited in part by technical challenges. Nuclear power faces persistent concerns about safety, nuclear waste, and potential weapons proliferation, despite past contributions to mortality prevention and climate change mitigation [232]. Most renewable energies tap diffuse intermittent sources often at a distance from the user population, thus requiring large-scale energy storage and transport. Develop- ing technologies can ameliorate these issues, as discussed below. However, apparent cost is the constraint that prevents nuclear and renewable energies from fully supplanting fossil fuel electricity generation. Transition to a post-fossil fuel world of clean energies will not occur as long as fossil fuels appear to the investor and consumer to be the cheapest energy. Fossil fuels are cheap only because they do not pay their costs to society and receive large direct and indirect subsidies [233]. Air and water pollution from fossil fuel extraction and use have high costs in human health, food production, and natural ecosystems, killing more than 1,000,000 people per year and affecting the health of billions of people [232,234], with costs borne by the public. Costs of climate change and ocean acidification, already substantial and expected to grow consider- ably [26,235], also are borne by the public, especially by young people and future generations. Thus the essential underlying policy, albeit not sufficient, is for emissions of CO 2to come with a price that allows these costs to be internalized within the economics of energy use. Because so much energy is used through expensive capital stock, the price should rise in a predictable way to enable people and businesses to efficiently adjust lifestyles and investments to minimize costs. Reasons for preference of a carbon fee or tax over cap-and-trade include the former’s simplicity and relative ease of becoming global [236]. A near-global carbon tax might be achieved, e.g., via a bi-lateral agreement between China and the United States, the greatest emitters, with a border duty imposed on products from nations without a carbon tax, which would provide a strong incentive for other nations to impose an equivalent carbon tax. The suggestion of a carbon fee collected from fossil fuel companies with all revenues distributed to the public on a per capita basis [237] has received at least limited support [238]. Economic analyses indicate that a carbon price fully incorpo- rating environmental and climate damage would be high [239]. The cost of climate change is uncertain to a factor of 10 or more and could be as high as, $1000/tCO 2[235,240]. While the imposition of such a high price on carbon emissions is outside the realm of short-term political feasibility, a price of that magnitude is not required to engender a large change in emissions trajectory. An economic analysis indicates that a tax beginning at $15/ tCO 2and rising $10/tCO 2each year would reduce emissions in the U.S. by 30% within 10 years [241]. Such a reduction is morethan 10 times as great as the carbon content of tar sands oil carried by the proposed Keystone XL pipeline (830,000 barrels/day) [242]. Reduced oil demand would be nearly six times the pipeline capacity [241], thus the carbon fee is far more effective than the proposed pipeline. A rising carbon fee is thesine qua nonfor fossil fuel phase out, but not enough by itself. Investment is needed in RD&D (research, development and demonstration) to help renewable energies and nuclear power overcome obstacles limiting their contributions. Intermittency of solar and wind power can be alleviated with advances in energy storage, low-loss smart electric grids, and electrical vehicles interacting with the grid. Most of today’s nuclear power plants have half-century-old technology with light-water reactors [243] utilizing less than 1% of the energy in the nuclear fuel and leaving unused fuel as long-lived nuclear ‘‘waste’’ requiring sequestration for millennia. Modern light-water reactors can employ convective cooling to eliminate the need for external cooling in the event of an anomaly such as an earthquake. However, the long-term future of nuclear power will employ ‘‘fast’’ reactors, which utilize,99% of the nuclear fuel and can ‘‘burn’’ nuclear waste and excess weapons material [243]. It should be possible to reduce the cost of nuclear power via modular standard reactor design, but governments need to provide a regulatory environment that supports timely construction of approved designs. RD&D on carbon capture and storage (CCS) technology is needed, especially given our conclusion that the current atmospheric CO 2level is already in the dangerous zone, but continuing issues with CCS technology [7,244] make it inappro- priate to construct fossil fuel power plants with a promise of future retrofit for carbon capture. Governments should support energy planning for housing and transportation, energy and carbon efficiency requirements for buildings, vehicles and other manu- factured products, and climate mitigation and adaptation in undeveloped countries. Economic efficiency would be improved by a rising carbon fee. Energy efficiency and alternative low-carbon and no-carbon energies should be allowed to compete on an equal footing, without subsidies, and the public and business community should be made aware that the fee will continually rise. The fee for unconventional fossil fuels, such as oil from tar sands and gas from hydrofracking, should include carbon released in mining and refining processes, e.g., methane leakage in hydrofracking [245– 249]. If the carbon fee rises continually and predictably, the resulting energy transformations should generate many jobs, a welcome benefit for nations still suffering from long-standing economic recession. Economic modeling shows that about 60% of the public, especially low-income people, would receive more money via a per capita 100% dispersal of the collected fee than they would pay because of increased prices [241]. Fairness: Intergenerational Justice and Human Rights Relevant fundamentals of climate science are clear. The physical climate system has great inertia, which is due especially to the thermal inertia of the ocean, the time required for ice sheets to respond to global warming, and the longevity of fossil fuel CO 2 in the surface carbon reservoirs (atmosphere, ocean, and biosphere). This inertia implies that there is additional climate change ‘‘in the pipeline’’ even without further change of atmospheric composition. Climate system inertia also means that, if large-scale climate change is allowed to occur, it will be exceedingly long-lived, lasting for many centuries. One implication is the likelihood of intergenerational effects, with young people and future generations inheriting a situation in which grave consequences are assured, practically out of their Assessing Dangerous Climate Change PLOS ONE | www.plosone.org 19 December 2013 | Volume 8 | Issue 12 | e81648 control, but not of their doing. The possibility of such intergen- erational injustice is not remote – it is at our doorstep now. We have a planetary climate crisis that requires urgent change to our energy and carbon pathway to avoid dangerous consequences for young people and other life on Earth. Yet governments and industry are rushing into expanded use of fossil fuels, including unconventional fossil fuels such as tar sands, tar shale, shale gas extracted by hydrofracking, and methane hydrates. How can this course be unfolding despite knowledge of climate consequences and evidence that a rising carbon price would be economically efficient and reduce demand for fossil fuels? A case has been made that the absence of effective governmental leadership is related to the effect of special interests on policy, as well as to public relations efforts by organizations that profit from the public’s addiction to fossil fuels [237,250]. The judicial branch of governments may be less subject to pressures from special financial interests than the executive and legislative branches, and the courts are expected to protect the rights of all people, including the less powerful. The concept that the atmosphere is a public trust [251], that today’s adults must deliver to their children and future generations an atmosphere as beneficial as the one they received, is the basis for a lawsuit [252] in which it is argued that the U.S. government is obligated to protect the atmosphere from harmful greenhouse gases. Independent of this specific lawsuit, we suggest that intergen- erational justice in this matter derives from fundamental rights of equality and justice. The Universal Declaration of Human Rights [253] declares ‘‘All are equal before the law and are entitled without any discrimination to equal protection of the law.’’ Further, to consider a specific example, the United States Constitution provides all citizens ‘‘equal protection of the laws’’ and states that no person can be deprived of ‘‘life, liberty or property without due process of law’’. These fundamental rights are a basis for young people to expect fairness and justice in a matter as essential as the condition of the planet they will inhabit. We do not prescribe the legal arguments by which these rights can be achieved, but we maintain that failure of governments to effectively address climate change infringes on fundamental rights of young people. Ultimately, however, human-made climate change is more a matter of morality than a legal issue. Broad public support is probably needed to achieve the changes needed to phase out fossil fuel emissions. As with the issue of slavery and civil rights, public recognition of the moral dimensions of human-made climate change may be needed to stir the public’s conscience to the point of action. A scenario is conceivable in which growing evidence of climate change and recognition of implications for young people lead to massive public support for action. Influential industry leaders, aware of the moral issue, may join the campaign to phase out emissions, with more business leaders becoming supportive as they recognize the merits of a rising price on carbon. Given the relative ease with which a flat carbon price can be made international [236], a rapid global emissions phasedown is feasible. As fossil fuels are made to pay their costs to society, energy efficiency and clean energies may reach tipping points and begin to be rapidly adopted. Our analysis shows that a set of actions exists with a good chance of averting ‘‘dangerous’’ climate change, if the actions begin now. However, we also show that time is running out. Unless a human ‘‘tipping point’’ is reached soon, with implemen- tation of effective policy actions, large irreversible climate changes will become unavoidable. Our parent’s generation did not know that their energy use would harm future generations and other lifeon the planet. If we do not change our course, we can only pretend that we did not know. Discussion We conclude that an appropriate target is to keep global temperature within or close to the temperature range in the Holocene, the interglacial period in which civilization developed. With warming of 0.8uC in the past century, Earth is just emerging from that range, implying that we need to restore the planet’s energy balance and curb further warming. A limit of approx- imately 500 GtC on cumulative fossil fuel emissions, accompanied by a net storage of 100 GtC in the biosphere and soil, could keep global temperature close to the Holocene range, assuming that the net future forcing change from other factors is small. The longevity of global warming (Fig. 9) and the implausibility of removing the warming if it is once allowed to penetrate the deep ocean emphasize the urgency of slowing emissions so as to stay close to the 500 GtC target. Fossil fuel emissions of 1000 GtC, sometimes associated with a 2uC global warming target, would be expected to cause large climate change with disastrous consequences. The eventual warming from 1000 GtC fossil fuel emissions likely would reach well over 2uC, for several reasons. With such emissions and temperature tendency, other trace greenhouse gases including methane and nitrous oxide would be expected to increase, adding to the effect of CO 2. The global warming and shifting climate zones would make it less likely that a substantial increase in forest and soil carbon could be achieved. Paleoclimate data indicate that slow feedbacks would substantially amplify the 2uC global warming. It is clear that pushing global climate far outside the Holocene range is inherently dangerous and foolhardy. The fifth IPCC assessment Summary for Policymakers [14] concludes that to achieve a 50% chance of keeping global warming below 2uC equivalent CO 2emissions should not exceed 1210 GtC, and after accounting for non-CO 2climate forcings this limit on CO 2emissions becomes 840 GtC. The existing drafts of the fifth IPCC assessment are not yet approved for comparison and citation, but the IPCC assessment is consistent with studies of Meinshausen et al. [254] and Allen et al. [13], hereafter M2009 and A2009, with which we can make comparisons. We will also compare our conclusions with those of McKibben [255]. M2009 and A2009 appear together in the same journal with the two lead authors on each paper being co-authors on the other paper. McKibben [255], published in a popular magazine, uses quantitative results of M2009 to conclude that most remaining fossil fuel reserves must be left in the ground, if global warming this century is to be kept below 2uC. McKibben [255] has been very successful in drawing public attention to the urgency of rapidly phasing down fossil fuel emissions. M2009 use a simplified carbon cycle and climate model to make a large ensemble of simulations in which principal uncertainties in the carbon cycle, radiative forcings, and climate response are allowed to vary, thus yielding a probability distribution for global warming as a function of time throughout the 21st century. M2009 use this distribution to infer a limit on total (fossil fuel+net land use) carbon emissions in the period 2000–2049 if global warming in the 21st century is to be kept below 2uC at some specified probability. For example, they conclude that the limit on total 2000–2049 carbon emissions is 1440 GtCO 2(393 GtC) to achieve a 50% chance that 21st century global warming will not exceed 2uC. A2009 also use a large ensemble of model runs, varying uncertain parameters, and conclude that total (fossil fuel+net land use) carbon emissions of 1000 GtC would most likely yield a peak Assessing Dangerous Climate Change PLOS ONE | www.plosone.org 20 December 2013 | Volume 8 | Issue 12 | e81648 CO 2-induced warming of 2uC, with 90% confidence that the peak warming would be in the range 1.3–3.9uC. They note that their results are consistent with those of M2009, as the A2009 scenarios that yield 2uC warming have 400–500 GtC emissions during 2000–2049; M2009 find 393 GtC emissions for 2uC warming, but M2009 included a net warming effect of non-CO 2forcings, while A2009 neglected non-CO 2forcings. McKibben [255] uses results of M2009 to infer allowable fossil fuel emissions up to 2050 if there is to be an 80% chance that maximum warming in the 21st century will not exceed 2uC above the pre-industrial level. M2009 conclude that staying under this 2uC limit with 80% probability requires that 2000–2049 emissions must be limited to 656 GtCO 2(179 GtC) for 2007–2049. McKibben [255] used this M2009 result to determine a remaining carbon budget (at a time not specified exactly) of 565 GtCO 2(154 GtC) if warming is to stay under 2uC. Let us update this analysis to the present: fossil fuel emissions in 2007–2012 were 51 GtC [5], so, assuming no net emissions from land use in these few years, the M2009 study implies that the remaining budget at the beginning of 2013 was 128 GtC. Thus, coincidentally, the McKibben [255] approach via M2009 yields almost exactly the same remaining carbon budget (128 GtC) as our analysis (130 GtC). However, our budget is that required to limit warming to about 1uC (there is a temporary maximum during this century at about 1.1–1.2uC, Fig. 9), while McKibben [255] is allowing global warming to reach 2uC, which we have concluded would be a disaster scenario! This apparently vast difference arises from three major factors. First, we assumed that reforestation and improved agricultural and forestry practices can suck up the net land use carbon of the past. We estimate net land use emissions as 100 GtC, while M2009 have land use emissions almost twice that large (,180 GtC). We argue elsewhere (see section 14 in Supporting Information of [54]) that the commonly employed net land use estimates [256] are about a factor of two larger than the net land use carbon that is most consistent with observed CO 2history. However, we need not resolve that long-standing controversy here. The point is that, to make the M2009 study equivalent to ours, negative land use emissions must be included in the 21st century equal to earlier positive land use emissions. Second, we have assumed that future net change of non-CO 2 forcings will be zero, while M2009 have included significant non- CO 2forcings. In recent years non-CO 2GHGs have provided about 20% of the increase of total GHG climate forcing. Third, our calculations are for a single fast-feedback equilibrium climate sensitivity, 3uC for doubled CO 2, which we infer from paleoclimate data. M2009 use a range of climate sensitivities to compute a probability distribution function for expected warming, and then McKibben [255] selects the carbon emission limit that keeps 80% of the probability distribution below 2uC. The third factor is a matter of methodology, but one to be borne in mind. Regarding the first two factors, it may be argued that our scenario is optimistic. That is true, but both goals, extracting 100 GtC from the atmosphere via improved forestry and agricultural practices (with possibly some assistance from CCS technology) and limiting additional net change of non-CO 2forcings to zero, are feasible and probably much easier than the principal task of limiting additional fossil fuel emissions to 130 GtC. We noted above that reforestation and improving agricultural and forestry practices that store more carbon in the soil make sense for other reasons. Also that task is made easier by the excess CO 2 in the air today, which causes vegetation to take up CO 2more efficiently. Indeed, this may be the reason that net land use emissions seem to be less than is often assumed.As for the non-CO 2forcings, it is noteworthy that greenhouse gases controlled by the Montreal Protocol are now decreasing, and recent agreement has been achieved to use the Montreal Protocol to phase out production of some additional greenhouse gases even though those gases do not affect the ozone layer. The most important non-CO 2forcing is methane, whose increases in turn cause tropospheric ozone and stratospheric water vapor to increase. Fossil fuel use is probably the largest source of methane [1], so if fossil fuel use begins to be phased down, there is good basis to anticipate that all three of these greenhouse gases could decrease, because of the approximate 10-year lifetime of methane. As for fossil fuel CO 2emissions, considering the large, long-lived fossil fuel infrastructure in place, the science is telling us that policy should be set to reduce emissions as rapidly as possible. The most fundamental implication is the need for an across-the-board rising fee on fossil fuel emissions in order to allow true free market competition from non-fossil energy sources. We note that biospheric storage should not be allowed to offset further fossil fuel emissions. Most fossil fuel carbon will remain in the climate system more than 100,000 years, so it is essential to limit the emission of fossil fuel carbon. It will be necessary to have incentives to restore biospheric carbon, but these must be accompanied by decreased fossil fuel emissions. A crucial point to note is that the three tasks [limiting fossil fuel CO 2emissions, limiting (and reversing) land use emissions, limiting (and reversing) growth of non-CO 2 forcings] are interactive and reinforcing. In mathematical terms, the problem is non-linear. As one of these climate forcings increases, it increases the others. The good news is that, as one of them decreases, it tends to decrease the others. In order to bestow upon future generations a planet like the one we received, we need to win on all three counts, and by far the most important is rapid phasedown of fossil fuel emissions. It is distressing that, despite the clarity and imminence of the danger of continued high fossil fuel emissions, governments continue to allow and even encourage pursuit of ever more fossil fuels. Recognition of this reality and perceptions of what is ‘‘politically feasible’’ may partially account for acceptance of targets for global warming and carbon emissions that are well into the range of ‘‘dangerous human-made interference’’ with climate. Although there is merit in simply chronicling what is happening, there is still opportunity for humanity to exercise free will. Thus our objective is to define what the science indicates is needed, not to assess political feasibility. Further, it is not obvious to us that there are physical or economic limitations that prohibit fossil fuel emission targets far lower than 1000 GtC, even targets closer to 500 GtC. Indeed, we suggest that rapid transition off fossil fuels would have numerous near-term and long-term social benefits, including improved human health and outstanding potential for job creation. A world summit on climate change will be held at United Nations Headquarters in September 2014 as a preliminary to negotiation of a new climate treaty in Paris in late 2015. If this treaty is analogous to the 1997 Kyoto Protocol [257], based on national targets for emission reductions and cap-and-trade-with- offsets emissions trading mechanisms, climate deterioration and gross intergenerational injustice will be practically guaranteed. The palpable danger that such an approach is conceivable is suggested by examination of proposed climate policies of even the most forward-looking of nations. Norway, which along with the other Scandinavian countries has been among the most ambitious and successful of all nations in reducing its emissions, nevertheless approves expanded oil drilling in the Arctic and development of tar sands as a majority owner of Statoil [258–259]. Emissions Assessing Dangerous Climate Change PLOS ONE | www.plosone.org 21 December 2013 | Volume 8 | Issue 12 | e81648 foreseen by the Energy Perspectives of Statoil [259], if they occur, would approach or exceed 1000 GtC and cause dramatic climate change that would run out of control of future generations. If, in contrast, leading nations agree in 2015 to have internal rising fees on carbon with border duties on products from nations without a carbon fee, a foundation would be established for phaseover to carbon free energies and stable climate. Supporting Information Table S1 (ODS) Table S2 (ODS) Table S3 (ODS) Text S1 (DOC) Acknowledgments We greatly appreciate the assistance of editor Juan A. An˜ el in achieving requisite form and clarity for publication. The paper is dedicated to Paul Epstein, a fervent defender of the health of humans and the environment, who graciously provided important inputs to this paper while battling late stages of non-Hodgkin’s lymphoma. We thank David Archer, Inez Fung, Charles Komanoff and two anonymous referees for perceptive helpful reviews and Mark Chandler, Bishop Dansby, Ian Dunlop, Dian Gaffen Seidel, Edward Greisch, Fred Hendrick, Tim Mock, Ana Prados, Stefan Rahmstorf, Rob Socolow and George Stanford for helpful suggestions on a draft of the paper. Author Contributions Conceived and designed the experiments: JH PK MS. Performed the experiments: MS PK. Wrote the paper: JH. Wrote the first draft: JH. 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