climate policy and opinion

The vast majority of scientists and researchers in the United States and throughout the world agree that manmade emissions are likely exacerbating climate change.  Despite U.S. news articles to the contrary, since 2007 no scientific body has disagreed with this position.  Therefore, it may be time to ask: What percentage of Americans need to believe that climate change is occurring for policymakers to take action?

Here is a random sampling of some June 2014 headlines, presumably done in response to the United States’s Environmental Protection Agency’s (EPA) June 2, 2014 proposal to regulate utilities’ greenhouse gas emissions:
Based on these headlines, it would seem clear that the majority of Americans believe global warming is real and support regulation of greenhouse gas emissions. 

But let’s take a longer-term perspective to try and better understand what Americans really think. The figure below shows America’s response to Stanford University, Yale University/ George Mason, the Pew Research Center, the University of Michigan (previously Brookings), and Gallup polls asking basically the same question: “Is global warming happening?”  While the differences between polls likely occur due to question wording, one stark realization stands out.  Since 2006, a majority (50-85%) of Americans have agreed that global warming is happening, but there is also variance among those numbers.  This variance is likely sufficient to influence policymakers actions, particularly when broken out on a state, regional, or congressional district level.  To better understand why the different polls fail to agree, we decided to look more closely at each of the survey’s wordings.
global warming opinions
Caption: Percent of total American public answering “Yes” to the question “Is global warming happening?”  The vertical bars give the polling error indicated by the survey authors.  Sources: Yale 2012, 2012 #2 , 2012 #3, 2013, 2014;  U Michigan/ Brookings 2012, 2012 #2, 2012 #3, 2013, 2013 #2; Stanford 2011, 2012, 2013, 2013 #2; Gallup 2012, 2013, 2014; Pew 2011, 2012, 2013, 2014, General
Stanford Woods Institute Senior Fellow Jon Krosnick has been conducting public opinion studies on climate change and related efforts since at least 2006.  Now run by Stanford University's Political Psychology Research Group, this survey question continues to be run roughly every year:
Q: You may have heard about the idea that the world's temperature may have been going up slowly over the past 100 years. What is your personal opinion on this - do you think this has probably been happening, or do you think it probably has not been happening?
A:  Yes, No, Don’t Know
The values we report in the figure above are the “Yes”; approximately 2-3% of respondents typically answer “Don’t Know”.  Likely this has the highest value of “yes” for all the polls because it emphasizes a slow change over the last century, and uses the word choice “probably”.
Yale/ George Mason
The Yale Project on Climate Change Communication and the George Mason University Center for Climate Change Communication have successfully collaborated for several years on this question.  The 2014 PIs, Anthony Leiserowitz, Geoff Feinberg, Seth Rosenthal, Edward Maibach, and Connie Roser-Renouf, have asked, roughly twice a year:
Q: Recently, you may have noticed that global warming has been getting some attention in the news. Global warming refers to the idea that the world’s average temperature has been increasing over the past 150 years, may be increasing more in the future, and that the world’s climate may change as a result. What do you think? Do you think that global warming is happening?
A: Yes, No, Don’t Know.
The values we report are the “Yes”; approximately 10-20% of respondents typically answer “Don’t Know”.   Similarly to the Stanford poll, this poll adds uncertainty by using “may”, so we would expect similar results.  Unfortunately, this poll had a much higher response of “Don’t Know”, possibly due to the final phrase “the world’s climate may change as a result”.  To compare the two, if you assume that half of all “Don’t Knows” would have answered “Yes”, this polling will then agree quite strongly with the Stanford finding.

Pew Research Center
The Pew Research Center is based in Washington, D.C. conducts nonpartisan, non-advocacy public opinion polling and demographic research.  They ask:
Q: Is there solid evidence the earth is warming? 
A: Yes (because of human activity), Yes (because of natural patterns), Yes (don't know), No, Mixed evidence/ Don't Know
The values we report are the “Yes (because of human activity)”; approximately 6-10% of respondents typically answer “Mixed evidence/Don’t Know”.  Likely this falls in the middle of the pack because they ask respondents about “solid evidence”, as opposed to the first two polls that express high levels of uncertainty.
U Michigan/ Brookings
This poll was initially housed at Brookings as the National Survey of American Public Opinion on Climate Change (NSAPOCC), and is now run through University of Michigan’s Center for Local, State, and Urban Policy’s National Surveys on Energy and Environment.   There was no noticeable change when switch occurred in December 2011.  They ask:
Q: Is there solid evidence that the average temperature on Earth has been getting warmer over the past four decades?
A: Yes, No, Don’t know
The values we report are the “Yes”; here again the “Don’t knows” are quite high at approximately 10-20%.   Likely this falls lower because they ask respondents about “solid evidence” in the “past four decades”, as opposed to the first two polls that express high levels of uncertainty over a century or longer.
Gallup has extensive experience running polls on just about any US policy question that exists. Of our surveys, they are the only ones to have consistently asked their question the same month (March) of every year since at least 2006.  Specifically:
Q: Which of the following statements reflects your view of when the effects of global warming will begin to happen: 
A: They have already begun to happen, they will start happening within a few years, they will start happening within your lifetime, they will not happen within your lifetime, but they will affect future generations, or they will never happen?
We report those who answered “They have already begun to happen”.  We suspect there is a low response rate in this instance because they question didn’t ask about “global warming”, it asked about “the effects of global warming”.  Also, this question has a much more specific timeline than the other questions.
Moving Forward
The above analysis illustrates two points.  First, question wording makes a difference in the polling results. Respondents are much more likely to agree with survey questions that ask about more gradual change over longer time periods and mention uncertainty, as opposed to questions that ask about fast and certain change over shorter time periods.   
Second, researchers may want to focus their efforts on answering the questions that lead to the “Don’t know” responses.  While we cannot infer how the 10-20% of respondents in the Stanford and Michigan polls might have answered if the question was clearer, it may be that with clearer questions and answers to them, these reports would show very different “Yes” results.
As scientists and engineers, we have an obligation to help those who “Don’t know” better understand climate change and the methods that can be used to mitigate emissions and adapt to the changes that may be in our future.  Although it’s not very easy to take a step outside of our normal comfort zone and explore the policy implications of our work, it’s important that we do so.  Yet to truly prepare for our future, we will need to understand not only the science of climate change and engineering to mitigate greenhouse gas emissions and adapt to climate change, but also the policy implications for the challenges of our time.

Acknowledgments: Blog a growth of previous work at AGU Science Policy Conference and CCAP).

Addendum:  David E. pointed out this excellent implication: "Clearly US politics cannot be explained on the basis of public opinion, and that one must look deeper in order to understand and explain why we make the political choices we do."