Scientific Calculator

Carol Browner, director of the White House Office of Energy and Climate Change Policy, trusts the latest Intergovernmental Panel on Climate Change (IPCC) report’s conclusions that anthropogenic carbon emissions are the primary cause of climate change. When pressed, the customary response of Browner and other proponents has been to rely on that oft-cited list of 2,500 scientists said to have given their full support of the report’s conclusions. Browner should check her facts.

Good science is not a democratic process where the vote of the majority or a consensus of scientists determines the inner workings of nature. The scientific method is a transparent process for acquiring new knowledge, laid bare for constant and withering critique, and may become generally accepted but is never “settled.” Some climate scientists, such as those exposed in the Climategate emails, continue to shortcut the scientific method while declaring their views as absolute. Politicians who shield themselves from criticism with the cloak of scientific absolutism are dangerous when contrary science is ignored when formulating public policy.

Browner, when pressed about opposing views of the state of climate science during a November 25, 2009, press conference, cited as her evidence the equivalent of a scientist head count. “[W]e have 2,500 of the world’s foremost scientists who are in absolute agreement that this [human-caused climate change] is a real problem and that we need to do something and we need to do something as soon as possible. What am I going to do, side with the couple of naysayers out there, or the 2,500 scientists? I’m sticking with the 2,500 scientists.” Let’s check Browner’s arithmetic.

After years of protests, the IPCC finally completed placing all reviewer comments and editor responses online.

The New Math

The 2007 IPCC Fourth Assessment Report AR4 (AR4, was the result of the work of the IPCC’s three working groups (WG), each with very specific responsibilities. The 996-page WG I, particularly Chapter 9, is the lynchpin of the entire climate debate because it reports the key finding that anthropogenic emissions are “very likely” causing climate change. Less interesting in this discussion are the reports of WG II (Impacts, Adaptation, and Vulnerability) and WG III (Mitigation of Climate Change).

The “very likely” conclusion is not a statistical product but, as discussed in a small report footnote, based on the “expert opinions” of the report authors. I liken this scientific shortcut to grading your own homework—speedy but suspect. Many statements, such as “Greenhouse gas forcing has very likely caused most of the observed global warming over the last 50 years” and “The primary source of the increased atmospheric concentration of carbon dioxide since the pre-industrial period results from fossil fuel use” are found in the critical Chapter 9, “Understanding and Attributing Climate Change” of WG I.

Browner’s comments are calculated to leave the impression that the science is unassailable because literally thousands of eminent climate scientists have diligently toiled over every word and phrase in AR4, fully resolved data inconsistencies and contrary opinion, and reached some sort of scientific certainty on the subject. The truth is far less pleasing.

The IPCC Fact Sheet on AR4 states that “More than 800 contributing authors and more than 450 lead authors (nominated and elected by the IPCC member countries) were involved in the writing of the AR4” and later notes that “More than 2,500 scientific expert reviewers were involved in the… review process of the AR4.” It’s a fair assumption that Browner is referring to the 2,500 reviewers (not even lead authors), so let’s begin examining the number of authors and reviewers of AR4 and determine how many are really involved in the writing and reviewing of the critical portions of AR4 that are in dispute.

Finally, Open and Transparent

After years of protests, the IPCC finally completed placing all reviewer comments and editor responses online for the first time last December. Combing through the comments was quite revealing. A quick fact check found that only 152 lead authors prepared the entire WG I report and 600 “scientific expert reviewers” checked their work. Approximately 308 reviewer comments were submitted on the final WG I draft. The controversial Chapter 9 unexpectedly cites a mere 10 lead authors and only 62 reviewers, many non-scientists. My review found that just five reviewers fully endorsed the entire 11-chapter WG I report in their comments.

My review also found a goodly number of reviewer comments were submitted by scientists who were critical of the WG I conclusions and would certainly take issue with being included in the 2,500 “in absolute agreement” cited by Browner. No matter how the numbers are massaged, the number of scientists directly involved in writing or reviewing the most critical conclusions of the entire AR4 (Chapter 9) number only 72 (which includes many non-scientist reviewers) falling far short of the 2,500 scientists that Browner cites as her authority.

The concerns of those scientists who dissent from AR4 is summed up rather well in a recent open letter from 300 U.S. scientists (with the number of signers increasing every day) that includes many former AR4 reviewers. The March 13, 2010 letter ( asks our leaders to “bring the focus back to credible science, rather than invented hyperbole.” Then there is that lists 31,486 American scientists who dissent from the conclusion of AR4.

Now is the time for the U.S. to take a leadership role in returning policy-neutral science to the forefront of the climate change debate rather than picking policies based on headcount or political agenda.

—Dr. Robert Peltier, PE, is POWER’s editor-in-chief.

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