The standard understanding of the scientific consensus on climate change is that “the earth is warming and that this warming is mainly caused by human activities.”
Think Progress recently ran a piece arguing that the most important thing one can do to fight climate change is to engage climate change skeptics in conversation to help them appreciate the need for urgent action. In line with that goal, the article opens with this image:
The above graphic conveys two things: first, getting skeptics to accept the scientific consensus on climate change is essential to convincing them of the need for urgent action. Second, in order for skeptics to accept the consensus, you have to convince them that the consensus is overwhelming - not just most scientists, but the vast majority of scientists.
The last post addressed the consensus definitions, methods and findings of the top four papers in the graphic (Oreskes 2004, Doran 2009, Anderegg 2010, and Cook 2013). This post will address the bottom three papers, starting with…
Definition of Consensus Position: The authors categorized scientists as agreeing with the consensus if they thought more than 50% of “global warming since the mid-20th century can be attributed to human-induced increased in atmospheric GHG [Greenhouse Gas] concentrations”. This is pretty much the standard definition.
Method: The researchers sent questionnaires to 7555 scientists, of which 1868 questionnaires were returned (a response rate of 29%). Questions investigated in this paper included:
Q1. What fraction of global warming since the mid-20th century can be attributed to human-induced increases in atmospheric GHG concentrations?
Q1b. What confidence level would you ascribe to the anthropogenic GHG contribution being more/less than 50%?
Q3. How would you characterize the contribution of the following factors to the reported global warming of ∼0.8 °C since preindustrial times: GHGs, aerosols, land use, sun, internal variability, spurious warming?
Respondents who selected any of the options of GHG > 50% in answer to Q1 were included in the “agreement” category. The answer “no warming” was included in the “disagreement” category. For Q3, responses were interpreted as “agreement” if GHGs were accredited with strong warming or with moderate warming if none of the other natural or anthropogenic factors were deemed to have caused strong warming. The responses ‘unknown”, “I do not know”, and “other” were categorized as “undetermined responses”.
Results: As a fraction of the total, the level of agreement based on Q1 and Q3 was 66% and 83%, respectively. That is, 66% of the respondents attributed at least 50% of recent global warming to human activities and 83% considered GHGs a significant factor in recent warming. As a fraction of those who expressed an opinion (i.e., excluding the undetermined answers), the level of agreement based on Q1 and Q3 was 84% and 86%, respectively.
Definition of Consensus Position: At one point, the authors define the consensus position position as agreement that human activity is “the primary cause of recent climate change”. However, they also state that being convinced “humans have contributed to global warming.” counts as agreement with the consensus. Which it doesn’t.
Method: Researchers e-mailed a survey to 7,197 professional member American Meteorological Society (AMS). Of these, 1,854 people completed at least some portion of the survey beyond the consent form (response rate of 26.3%). Of these, 375 participants were sent a follow-up question, which received 270 responses. The question was about the relative contributions of human activity and natural events to recent warming, to which there were four possible answers: “Mostly by human activity,” “Mostly by natural events”, “More-or-less equally by human activity and natural events”, “I do not believe we (scientists) know enough yet”.
Results: “Per Stenhouse et al: “93% of actively publishing climate scientists indicated they are convinced that humans have contributed to global warming. Our findings also revealed that majorities of experts view human activity as the primary cause of recent climate change: 78% of climate experts actively publishing on climate change, 73% of all people actively publishing on climate change, and 62% of active publishers who mostly do not publish on climate change.” The following table provides additional results:
Definition of Consensus Position: When compared with pre-1800’s levels, mean global temperatures have generally risen and human activity is a significant contributing factor in changing mean global temperatures. This is not the standard definition of the consensus, which is that human activity is mainly responsible for recent global warming.
Method The researchers surveyed a sample of 1868 scientists and received 698 responses (37.4% response rate). The survey included the question: ‘When compared with pre-1800’s levels, do you think that mean global temperatures have generally risen, fallen, or remained relatively constant?’ If respondents believed global temperatures had risen, they were asked about the role of human activity in global warming. The researchers also broke down the respondents by field of study: Forty-seven percent of the respondents were either in agricultural (19%) or biological (28%) scientists. Three percent of the respondents were in atmospheric science or meteorology. There was no separate category of “climate science”.
Results: “[W]hen asked 'When compared with pre-1800's levels, do you think that mean global temperatures have generally risen, fallen, or remained relatively constant?', 93.6% of respondents across all disciplines indicated that they thought temperatures have risen…Of those who indicated that they believed temperatures have risen, 98.2% indicated they believe that 'human activity is a significant contributing factor in changing mean global temperatures'. Together, these two facts reveal that 91.9% of scientists surveyed believed in anthropogenic climate change.” Note that 52% of the respondents endorsed “None of my research concerns climate change or the impacts of climate change.”
Ok, that’s it for now.
Next: Do these studies actually demonstrate an overwhelming scientific consensus on climate change?
Anderegg, W.R.L., Prall, J.W., Harold, J., and Schneider, S.H. 2010. Expert credibility in climate change. Proceedings of the National Academy of Sciences 107: 27. 12107–12109. https://doi.org/10.1073/pnas.1003187107
Carlton, JS, Perry-Hill, R, Huber, M, and Prokopy, LS. 2015. The climate change consensus extends beyond climate scientists. Environmental Research Letters https://doi.org/10.1088/1748-9326/10/9/094025
Cook, J. Nuccitelli, D., Green, S.A., Richardson, M., Winkler, B., Painting, R., Way, R. Jacobs, P., and Skuce, A. 2013. Quantifying the consensus on anthropogenic global warming in the scientific literature. Environmental Research Letters 8: 2. https://iopscience.iop.org/article/10.1088/1748-9326/8/2/024024;
Doran, P.T. and Zimmerman, M.K. 2009. Examining the scientific consensus on climate change. EOS 90: 3, 22–23. DOI: 10.1029/2009EO030002. https://doi.org/10.1029/2009EO030002
Oreskes, N. (2004). "The Scientific Consensus on Climate Change." Science 306(5702): 1686-1686. DOI: 0.1126/science.1103618 https://science.sciencemag.org/content/306/5702/1686.summary
Stenhouse, N., Maibach, E., Cobb, S., Ban, R., Bleistein, A., Croft, P., Bierly, E., Seitter, K., Rasmussen, G., and Leiserowitz, A. 2014: Meteorologists’ views about global warming: A survey of American Meteorological Society professional members. Bulletin of the American Meteorological Society 95: 1029–1040. https://doi.org/10.1175/BAMS-D-13-00091.1
Verheggen, B., Strengers, B., Cook, J. van Dorland, R., Vringer, K., Peters, J. Visser, H., and Meyer, L. 2014. Scientists’ views about attribution of global warming. Environmental Science & Technology 48: 16. 8963–8971, DOI: 10.1021/es501998e https://doi.org/10.1021/es501998e