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. So is that what the studies in this graphic show? Let’s find out.
Definition of Consensus Position: “Most of the observed warming over the last 50 years is likely to have been due to the increase in greenhouse gas concentrations.” This is close to the standard definition (see above).
Method: Analyzed 928 abstracts of papers identified via the keyword search “climate change”. (Abstracts are brief (typically one-paragraph) summaries of the rationale/purpose, methods, and findings). The papers did not have to be about climate change nor written by climate scientists. All that was required was that they be in peer-reviewed scientific journals and their authors had chosen “climate change” as one of their keywords for searches.
Results: If a paper’s abstract did not explicitly disagree with the consensus, Oreskes counted it as agreeing with the consensus. Doesn’t matter if the paper had been written by a paleontologist and was about climate-related migrations of now-extinct species during the Eocene. If that author did not explicitly reject modern-day climate change in the paper’s abstract, then the authors was counted as supporting the consensus. Using this method, Oreskes concludes that 100% of the scientists support the consensus.
Definition of Consensus Position: when compared with pre-1800s levels, global temperatures have generally risen and human activity is a significant contributing factor in changing mean global temperatures. Note this is not the standard definition of consensus (see above). That humans make a “significant” contribution to global warming is different than saying “warming is mainly caused by human activity”. There are plenty of public figures saddled with the label “denier” who actually accept the earth is warming and humans are part of the reason. For examples, see “What Does It Mean To Be a Climate Change Denier, Part VI”
Method: The researchers sent an online survey to 10,257 Earth scientists, generating survey responses from 3,146 people. The survey asked: 1) “When compared with pre-1800s levels, do you think that mean global temperatures have generally risen, fallen, or remained relatively constant?”, and 2) “Do you think human activity is a significant contributing factor in changing mean global temperatures?”
Results: Of survey participants, 90% answered “risen” to question 1 and 82% answered yes to question 2. In other words, 73.8% of the respondents believed global temps have risen and humans are a significant contributing factor in the change in global temperatures.
Definition of Consensus Position: Broad agreement with the tenet that “it is ‘very likely’ that anthropogenic greenhouse gases have been responsible for ‘most’ of the ‘unequivocal’ warming of the Earth's average global temperature in the second half of the 20th century.” This is pretty close to the standard definition of the scientific consensus given at the top of this post.
Method: The researchers used a dataset of 1,372 climate researchers and winnowed it down to those who had authored or co-authored at least 20 climate-related publications, reducing the dataset to 908 researchers. The researchers define “credibility” in terms of number of papers authored or coauthored and reduce the list to 50 climate scientists with the most publications. By this definition, a researcher with 400 papers is more credible than one with 80 papers.
Results: Of the 50 climate change scientists who had authored or co-authored the most climate-related papers, 98% were categorized as supporting the consensus. Of the top 100 climate scientists (as defined by number of publications), 97% supported the consensus; of the top 200, 97.5% supported the consensus. That leaves 708 climate scientists in the survey (78% of the total) unaccounted for - all of whom had published at least 20 peer-reviewed papers. The authors do not reveal how many of this much larger group supported or did not support the consensus.
Definition of Consensus Positions: Explicitly stating that humans are the primary cause of recent global warming or are causing global warming, or references to anthropogenic global warming/climate change as a known fact; or implying that humans are causing global warming, e.g “research assumes greenhouse gas emissions cause warming without explicitly stating humans are the cause.”
Method: Researchers examined 11 944 climate abstracts from 1991–2011 matching the topics 'global climate change' or 'global warming'. Papers were categorized as endorsing the scientific consensus if the abstracts included explicit or implicit statements of agreement with the consensus (as defined by the authors) The researchers then solicited the papers’ authors to self-rate their agreement with the consensus.
Results:. A total of 2142 papers were self-rated by their authors. Of these, 62.7% were self-rated as endorsing the consensus, 35.5% had no opinion or were undecided, and 1.8% explicitly rejected the consensus. Cook et al came up with the 97% support for the consensus by ignoring the “no opinion/undecided” papers.
Whew! That’s it for now. In the next post, I’ll address the final three papers cited as documenting overwhelming scientific consensus on climate change: Verheggen 2014, Stenhouse 2014, and Carlton 2015.
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