EPA Administrator Scott Pruitt said on CNBC:
“I think that measuring with precision human activity on the climate is something very challenging to do, and there’s tremendous disagreement about the degree of impact, so no, I would not agree that it’s a primary contributor to the global warming that we see.”
This is consistent with Pruitt’s previous public statements and writings on climate change. It is also false and misleading.
There is not “tremendous disagreement” among scientists but a strong consensus that humans are the primary cause of recent climate change. The consensus exists because of clear and convincing evidence from empirical observations of temperatures and many different Earth systems, fundamental and tested laws of physics and insights gained from model simulations of how the climate behaves under changed conditions. Nearly 30 years of review of the evidence by a variety of scientific organizations have led the non-partisan U.S. National Academy of Sciences, as well as many other national science academies and scientific associations, to conclude that the climate is changing and humans very likely are the major cause.
The most comprehensive and carefully peer-reviewed assessment of the science of climate change is conducted every five to six years by the Intergovernmental Panel on Climate Change (IPCC). The IPCC’s most recent assessment of the physical science of climate change, published in 2013, was written by several hundred scientists from 39 countries, including the U.S., with expertise in climate science and related fields and who work for universities, scientific institutions, private businesses and government science agencies.
The author team examined over 9200 scientific publications to produce a 2000-plus page report on the state of knowledge about climate change. Drafts of the report went through two rounds of formal review in which over 1000 reviewers submitted over 50,000 comments. Fifty review editors oversaw the review process, charged with assuring that issues identified by the reviewers were appropriately resolved for the final report [Disclosure: I served as a review editor for the IPCC’s 2014 companion report on the impacts of climate change]. The final report was accepted by the roughly 100 national governments that are members of the IPCC, certifying it as presenting a “comprehensive, objective and balanced view” of climate science.
So what does the IPCC report say? First off, it is clear from the report that Pruitt is correct that measuring the human effect on climate change with precision is challenging. Human drivers of climate change include changes in the atmospheric concentrations of a variety of gasses and aerosols emitted by human activities, as well as their indirect effects through changes in clouds and the reflectivity of the Earth’s surface. There are also natural drivers that include changes in solar irradiance and aerosols from volcanic activity. Scientists can and have measured the effects of both human and natural drivers of climate change on the Earth’s energy budget and the climate. There are uncertainties in the measurements. But, despite the uncertainties, measures are sufficiently accurate to be confident that the human drivers have had a much greater impact on the Earth’s energy budget than the natural drivers, at least 10 times greater and possibly more than 45 times greater.
Turning to the climate itself, the IPCC concluded that it is extremely likely (95 to 100% probability) that more than half of the observed increase in global average surface temperature from 1951 to 2010 was caused by humans. The evidence comes from multiple sources.
Pruitt’s statements on climate change strongly suggest that he has not examined the scientific evidence with care and an open mind.
The time path of observed changes in global average surface temperature corresponds strongly with the time path of measured changes in the energy budget from the combined effects of human and natural drivers, and is inconsistent with and cannot be explained by changes in natural drivers alone. The geographic distribution of warming (greater at high northern latitudes than in low latitudes, greater over continental interiors than coasts and over oceans) matches the physics of human-caused climate change and not that of natural variability. Observed warming in the Earth’s troposphere (lower atmosphere) and cooling of the stratosphere (high atmosphere) matches the physics of greenhouse gas warming and not increases in solar output. Observed changes in ocean heat content, sea level, sea ice, snow cover and atmospheric water vapor also support the conclusion that humans have changed and are changing the climate. Taken together, the multiple lines of evidence have led the IPCC, and nearly all scientists who work in this field, to conclude that most of the observed warming is human caused.
Can you find scientists who disagree with the findings of the IPCC? Yes, you can find some, but they are very much in the minority. A 2009 study found that, of 908 scientists with at least 20 peer-reviewed scientific publications on climate, roughly 90 percent (817 scientists) concur with and 10 percent (93 scientists) dispute the IPCC’s conclusion that humans are responsible for most of the climate change observed in the second half of the 20th century. But if you limit your search to the 200 scientists with the most climate science publications, only 5 dispute the conclusion, or 2.5 percent. The other 195, or 97.5 percent, are in agreement with it. If you limit your search further to the 50 most productive scientists with the largest number of climate science publications, only 1 disputes the conclusion while 49 support it.
Pruitt’s statements on climate change strongly suggest that he has not examined the scientific evidence with care and an open mind. Given the extensive evidence, the judgments reached on the evidence by numerous credible and scientifically expert bodies, and the widespread consensus shared by scientists with expertise on climate, the burden of proof is on Mr. Pruitt to demonstrate that the risk of human-caused climate change is so remote that actions to reduce emissions of greenhouse gases are unwarranted. If he tries to make such a case, which he must if he proceeds as intended to dismantle the Clean Power Plan and other climate change policies, it is incumbent on him to tell the American people what scientific evidence and reports, and which scientific experts, he is relying on when he offers his lawyerly opinion that humans are not a primary driver of climate change.
Pruitt’s lack of science literacy may have been understandable when he was a state attorney general and saw his job as including affixing his name to letters written by oil industry lobbyists. But he is now the Administrator of the U.S. Environmental Protection Agency, an agency with the mission to “protect human health and the environment” while ensuring that “national efforts to reduce environmental risk are based on the best available scientific information.” When sworn into office by Justice Samuel Alito Jr., Pruitt took an oath: “I will well and faithfully discharge the duties of the office on which I am about to enter. So help me God.” Mr. Pruitt has a lot of science homework to do if he is to make good on his oath and bring his science grade up to a passing level.
Give Mr. Pruitt a call at 202-564-4700, or write him at firstname.lastname@example.org, and ask him to faithfully discharge his duties by taking an honest look at the science.
Anderegg, W., J. Prall, J. Harold and S. Schneider. Expert credibility in climate change. Proceedings of the National Academy of Sciences, July 6, 2010. http://www.pnas.org/content/107/27/12107.full
DiChristopher. T. EPA chief Scott Pruitt says carbon dioxide is not a primary contributor to global warming. CNBC, March 9, 2017. http://www.cnbc.com/2017/03/09/epa-chief-scott-pruitt.html.
Gleick, P. Joint statements on climate change from national academies of science around the world. ScienceBlogs, January 17, 2017. http://scienceblogs.com/significantfigures/index.php/2017/01/17/joint-statements-on-climate-change-from-national-academies-of-science-around-the-world/.
IPCC, 2013: Climate Change 2013: The Physical Science Basis. Contribution of Working Group I to the Fifth Assessment Report of the Intergovernmental Panel on Climate Change. Stocker, T.F., D. Qin, G.-K. Plattner, M. Tignor, S.K. Allen, J. Boschung, A. Nauels, Y. Xia, V. Bex and P.M. Midgley (eds.). Cambridge University Press, Cambridge, United Kingdom and New York, NY, USA, 1535 pp. [A summary of the report can be found here: https://www.ipcc.ch/pdf/assessment-report/ar5/wg1/WG1AR5_SPM_FINAL.pdf].
IPCC, Climate Change 2013, Questions About the Development of the Report. https://www.ipcc.ch/report/ar5/wg1/docs/WG1AR5_Questions.pdf
Sundance. Justice Samuel Alito Swears in EPA Administrator Scott Pruitt. The Last Refuge, February 17, 2017. https://theconservativetreehouse.com/2017/02/17/justice-samuel-alito-swears-in-epa-administrator-scott-pruitt/
U.S. Environmental Protection Agency. Our Mission and What We Do. https://www.epa.gov/aboutepa/our-mission-and-what-we-do