The Scientific Consensus

Who believes what?

Consensus means different things to different people, and much debate remains within climate science. However, what can be said is that there exists a strong consensus that humans are now playing a significant role in the climate, primarily due to the emission of greenhouse gases.


The Intergovernmental Panel on Climate Change (IPCC) was established by the United Nations and the World Meteorological Organization to regularly summarize the current state of climate science.

Within the IPCC, there are three working groups that cover different areas.

  • Working Group I (WGI) is “The Physical Science Basis.”1 It is our best understanding of the science behind climate change and it is what we will focus on in this presentation.

  • Working Group II (WGII) is “Impacts, Adaptation and Vulnerabilities.”2 It is what is believed will happen as result of further warming.

  • Finally, there is Working Group III (WGIII) which is “Mitigation of Climate Change,” or solutions to the problem.3

The IPCC does not do original reseach. The reports are syntheses of the available scientific literature. The cutoff for consideration for new material was in 2005.


The Fourth Assessment Report (AR4) WGI has 619 coordinating lead authors, lead authors, and contributing authors. These are the people who actually worked on the report. The scientists from the US are nominated by their peers and coordinated through the State Department.

The 619 authors do not include “expert reviewers”. Skeptics often tout expert reviewer status as a way of alleging credibility, but no expertise in climate science is required. In total, WGI addressed over 30,000 reviewer comments.4

Summary for Policymakers

Each working group includes a Summary for Policymakers (SPM), written by lead authors of the report. The AR4 WGI SPM5 has 33 authors representing academic institutions from 16 countries, with the US contributing by far the most.

The SPMs are consensus documents and therefore conservative, the exact opposite of what the skeptics often portray. Negotiators from each UN nation must agree to the precise wording of the summary, but the politicians cannot override the scientists. The conclusions must encompass the views of the most skeptical party, which includes the governments of the United States, China, and Saudi Arabia to name a few.

The WGI SPM concludes that “Warming of the climate system is unequivocal.” That is, it is a fact that the world has warmed. Significantly, “Most of the observed increase in global average temperatures since the mid-20th century is very likely [i.e. greater than 90 percent probability] due to the observed increase in anthropogenic greenhouse gas concentrations.”

Consensus census

In addition to the IPCC, the world’s scientific societies have overwhelmingly endorsed the science of anthropogenic global warming. The membership statistics below are given not to imply unanimity, but to establish the significance of the societies.

Among them:

Scientific Societies

Science academy signatures

These are the signatures of each science academy’s president.

“Consensus” vs. the Skeptics

Skeptics view declarations of “consensus” as a way of stifling debate. In particular, they see consensus statements from the world’s scientific societies as alarmist propaganda and not representative of their membership. Some of these statements were drafted by expert panels drawn from the society’s membership. Others are written by elected officials. Many were first drawn up years ago and have been renewed several times. If the membership is displeased, they’ve continued to elect the wrong leadership.

The Oregon Petition

The most common tactic that skeptics use to allege that no consensus exists is by listing individual scientists who don’t agree. These lists have come in various forms over the years, such as the Leipzig Declaration, the Inhofe 400, or the Manhattan Declaration12, but the most prominent example is the Oregon Petition.13 The petition was first circulated in 1998 and was recently resurrected and updated, gathering many new signatures.

This was organized by the Oregon Institute of Science and Medicine (OISM) for the purpose of convincing the US government to reject Kyoto. The OISM was founded by Arthur B. Robinson and currently includes 8 “faculty members,” which includes Robinson and his two sons. Two of the “faculty members” are dead. Before global warming, the OISM focussed on nuclear war survival skills and methods to slow aging.

Cover letter and a tobacco interlude

The campaign to obfuscate global warming is often compared to that surrounding tobacco. They intersect with the author of the Oregon Petition’s cover letter, Frederick Seitz. Seitz was president of the National Academy of Sciences (NAS) from 1962 to 1969 and co-founder of the George Marshall Institute, a think tank founded to support Reagan’s missile defense program. His letter still accompanies the latest version of the petition, updated in 2007, months before his death at the age of 97.

Before turning to global warming issues, Seitz was hired by the tobacco industry to direct its $45 million medical research program. Seitz said that he was given “absolutely free rein to decide how the money was spent,” with one exception: “They didn’t want us looking at the health effects of cigarette smoking.”14 Contrast that with the reasons former RJR CEO Colin Stokes gave for funding the research. Among them:15

  • to “respond directly to a fundamental attack on our business”

  • to “refute the criticisms against cigarettes” so as to “remove government’s excuse for imposing heavy taxes on the product.”

  • and “there a large number of crucial questions that need scientific answers in the area of smoking and health.”

Instead of answering those questions, they investigated every other cause of smoking and heart disease except smoking. 16

Seitz was asked if his research provided political cover for the tobacco companies. He replied, “I’ll leave that to the philosophers and priests.”17

“Review of information on the subject of global warming”

Attached to the original Oregon Petition was an “eight page review of information on the subject of global warming.”18 The lead author was Arthur B. Robinson himself, a biochemist. The other two authors were Sallie Baliunas and Willie Soon, both astrophysicists and “senior scientists” at the George Marshall Institute. Robinson’s son Zachary also contributed. This version of the paper was formatted to make it appear that it was published in The Proceedings of the National Academy of Sciences. Given Seitz’s past presidency it may have seemed to some that the NAS was endorsing it, leading them to issue a statement denouncing the petition.19

The latest version of the paper drops Baliunas, and the Robinson son Zach is swapped for Noah.20 It was published in The Journal of American Physicians and Surgeons (JPANDS). Aside from having nothing to do with climatology, JPANDS is a forum for quack medicine, including the claim that HIV doesn’t cause AIDS.21

Persistence pays off

The original petition eventually collected 17,000 scientist signatures. According to Robert Park, who was the spokesman for the American Physical Society at the time, “Virtually every scientist in every field got it.”22 The current version has added 14,000 signatures.

There are over 10 million people with degrees in science and engineering in the US, and more than 500,000 science or engineering PhDs.23 That is a very large pool to draw upon if your only qualification is that you are skeptical of global warming.

31,000 scientists

The Oregon Petitions website categorizes24 its 31,000 scientists like this:

A third of the signers are engineers, or people with generic scientific degrees. 4000 signers were medical doctors, computer scientists and mathematicians. The most relevant category “Atmospheric, environmental, and earth” has 3700 names. They are broken down further.

Although all of the earth sciences are important to the study of current and past climate, anthropogenic global warming depends on the physics of the atmosphere. Atmospheric scientists are broken down further still:

More than half of the names are meteorologists, who tend to be TV and radio weather people (see section 8 for the differences between weather and climate). The most relevant are the 40 climatologists, and 114 atmospheric scientists. These are the people whose profession is most relevant to the study of these issues, yet they make up about half of a percent of the names on the petition.

Scientific American survey of Oregon Petition signatories

While some fields are clearly not relevant, others are at least applicable to the study of the greenhouse effect, or the broader climate. Scientific American took a random sample of 30 of the 1400 signatories from the original petition claiming to hold a Ph.D. relevant to climate science.25

Of the 20 they were able to contact, only 1 was actually doing climate-related research. Scientists who are skeptical of global warming can publish their arguments in a peer reviewed journal. That is how science works. However, as we will see shortly, this is extremely rare.

Prall Survey26

Science is built on the work of others. One way to measure the credibility of a scientist is by the number of times his or her work is referenced by other scientists. Jim Prall, a systems administrator for the University of Ontario, has painstakingly catalogued the most cited authors on climate change.

He has compiled the names of all 619 authors of the AR4 WGI report, plus signers of both “activist” (pro consensus) and “skeptic” petitions and letters. He also added names from unsigned lists of skeptics, plus other prominent scientists and co-authors. As of July 2009, his list includes over 2600 names and he’s collected statistics on 1800 of them.

Of the 500 most cited authors in the Google Scholar “physics, astronomy, and planetary scientists” catagory, 184 are on activist lists, while 23 are on lists of skeptics.

Prall has also collected the number of papers by each author that reference “climate.” This reshuffles the list, bumping some scientists from the top 500 and adding others, but the results are nearly the same. Of the 500 most published authors referencing “climate,” 182 are on activist lists and 20 are on lists of skeptics.

So, despite claims of “thousands of scientists” disagreeing with the consensus position, of the scientists with the most significant publishing record, activists outnumber skeptics by about 8 to 1.

Doran & Kendall Zimmerman Survey27

But what about the scientists who haven’t publicly committed to a “side”? What do they believe?

EOS is the newsletter of the American Geophysical Union (AGU). It recently published a survey of over 3000 earth scientists, 90% of whom hold PhDs. Unlike a petition, where all signers agree with a single position, a scientific survey represents the differing views of a population based on a random sample.

The survey found that 82% “think human activity is a significant contributing factor in changing mean global temperatures.” It also found that the more active the scientist was, and the more specialized they were in the climate field, the more likely they were to believe that human activty was a significant factor. Of the 79 active publishers on climate change in the survey, all but two believed this. In contrast, just 58% of the broader public believe this according to a recent Gallup poll.

Oreskes survey

No discussion of the consensus on climate change can be complete without covering the Oreskes Survey.

Naomi Oreskes is a professor of History and Science Studies. She has a bachelor’s degree in mining geology, and her Ph.D. is in geological research and the history of science. In 2004, she analyzed 928 abstracts from articles published between 1993 and 2003 in refereed scientific journals listed in the ISI Web of Science database with the keywords “global climate change.”28

She found:

  • 75% explicitly or implicitly endorsed the consensus position.

  • 25% dealt with climate measuring methods or climate of the past, stating no position on human caused climate change

  • No abstract in the survey rejected the consensus position

What it does not say (and many people on both sides get this wrong):

  • That no skeptical papers exist.

  • That no skeptical scientists exist.

The 929th abstract might well have included a skeptical position, but of those in the sample, they didn’t exist. This means that they are very, very rare.

Peiser survey

Benny Peiser, a social anthropologist, wrote a letter to Science challenging the conclusions of the Oreskes survey. His letter was rejected by the editors.29 Peiser searched all documents including editorials and letters, and included the social sciences and arts and humanities databases. Oreskes excluded those databases and only included articles that met the standard of peer review.

He initially found 34 articles that he claimed “reject or doubt” the consensus opinion30 but he now believes that only 1 meets the criteria. “I have publicly withdrawn this point of my critique” he writes.31 The remaining article was published in the American Association of Petroleum Geologists journal, The AAPG Bulletin. This article was specifically excluded from Oreskes’ survey since it was a summary article and statement by the trade group and not an original peer reviewed article.

Peiser says he doesn’t doubt that the “overwhelming majority of climatologists” agree that the current warming period is mostly due to human impact, but he doesn’t believe that it is unanimous. But Oreskes didn’t say that it was unanimous.

Schulte survey

The skeptics are still attacking the Oreskes survey.

One example comes from Klaus-Martin Schulte, an endocrinologist. It was published in the journal Energy and Environment (E&E), which was also responsible for the wavy graph of CO2 measurements in the introduction. Peiser is on the editorial board of E&E and the editor is a political scientist. The paper claims to revisit and update the Oreskes study to 2007. Originally, the editor wasn’t going to accept it because, “it was a bit patchy and nothing new.”32 Nevertheless, it was published some months later.33 The paper includes all 34 of the erroneously classified papers from Peiser’s unpublished letter to Science.34

A skeptical website touting the Schulte survey concludes, “By contrast [to the IPCC's authors], the ISI Web of Science database covers 8,700 journals and publications, including every leading scientific journal in the world!”35 Not surprisingly, you won’t find the Schulte survey in the ISI Web of Science database, because E&E is not one of those 8,700 leading journals.36

Turning the tables (and then turning them back)

When the “no consensus” argument fails, a different tactic is used. Skeptics are often accused of being in the pocket of industry, so they have proposed an argument of their own: scientists have put forth a false crisis to receive research grants. If you frame your research as it relates to climate change, you are more likely to receive funding so it’s in the scientists’ best interest to keep the global warming ball going. That, they say, is the reason so many scientists believe what they do.

If it’s all driven by money, who has the most to lose?

The chart shows the total dollars spent on climate change by the US federal government from 2001 to 2007.37 To the right of that is ExxonMobil’s profit for the same time period.38 Not the revenue, but the profit. This figure doesn’t include the other oil companies, nor does it include the profits from other fossil fuels, such as coal or natural gas.

We accept that energy costs money because it gives us so much. What should be equally obvious is the importance of a stable climate. For the last 10,000 years, the climate has remained remarkably stable and this has allowed civilization to flourish. Over the next 50 years, world population will approach 10 billion. Knowing what the climate is doing doing now and will do in the future is vital to the food and water supply of the world. How much is this worth?

Think tank roundup

The campaign to prevent or slow regulation of greenhouse gases overwhelmingly originates from think tanks dedicated to promoting free market ideals. The US fossil fuel industry had funded many of these think tanks under the guise of fostering the free market. In recent years, however, industry has scaled back or eliminated financial support as the political winds have changed.

The think tanks persist in their message however, having essentially created a cottage industry for climate change skepticism. We’ve already mentioned the George Marshall Institute, but that’s just the start. Among the most influential:

  • The Competitive Enterprise Institute (CEI) is most famous for the marketing campaign, “CO2. They call it pollution. We call it life.”39 The institute’s founder proposes a free market solution to saving endangered species: put the ones we care about in zoos.40

  • Cato Institute Senior Fellow Patrick Michaels is the most prolific television climate scientist contrarian. Also fellows at the Cato institute are the comedic magic act Penn and Teller who extoll the virtues of deregulation on their own Showtime series.41

  • The Heartland Institute hosts the annual “International Conference on Climate Change” where skeptics of all levels of expertise are welcome.42

These think tanks publish books and position papers in addition to providing the cable talk shows with a constant stream of pundits to promote their ideology. All of this is really cheap compared to satellites, arctic expeditions, or super computers.

Consensus != science

Even if they accept that a consensus exists, skeptics will say that “Science is not done by consensus” which is true. However, policy is. You weigh the scientific evidence and then act on it.

Policymakers would be irresponsible to ignore the warnings of the scientific community with the hope that the consensus position is wrong and an increasingly insignificant minority is right. If you’ve heard the expression “prepare for the worst, but hope for the best,” what people are doing instead is hoping for the best, preparing for the best, and ignoring the rest. That is not a rational response to a potentially grave problem.


  1. (IPCC, 2007) Online here

  2. (IPCC, 2007) Online here

  3. (IPCC, 2007) Online here

  4. (IPCC, 2007) Online here. A single skeptic — Vincent Gray, a New Zealand coal scientist – was responsible for half of the comments on the second draft of chapter 9 . Example of one comment. “Insert after ‘Bayesian’ ‘(or super-guesswork)’” Response? “Rejected. Bayesian analyses are not guesswork.” Sixty-eight of his comments argued for the replacement of “anthropogenic” with other words, and dozens more comments argued for similar word changes. []

  5. AR4 WGI Summary for Policymakers can be accessed directly here

  6. (AAAS Board of Directors, 2006) Online here

  7. (ACS, 2007) Online here

  8. (AGU, 2007) Online here

  9. (AMS Council, 2007) Online here

  10. (Peters, et al., 2006) Online here

  11. (Joint Academies, 2008) Online here

  12. Leipzig Declaration (SEPP, 1995, 2005), Inhofe 400 (Morano, 2007), Manhattan Declaration (International Climate Science Coalition & Heartland Institute, 2008)

  13. (Global Warming Petition Project, 2008) Website here

  14. (Hertsgaard, 2006) Online here. The website (Schulz, 2006) purports to debunk the Vanity Fair article by claiming that Seitz’s work didn’t try to hide the effects of tobacco

  15. (Stokes, 1979) Online here. Also see (Hobbs, 1984) online here. CTR’s mandate is described on page 2, under the heading “Organization and policy.”

  16. (Kouri, 1997) Online here. (Fyock, 1979) Online here. (Holtzman, 1989) Online here

  17. (Hertsgaard, 2006) Online here.

  18. (Robinson, Baliunas, Soon, & Robinson, 1998) Archived here

  19. (Council of the National Academy of Sciences, 1998) Online here

  20. (Robinson, Robinson, & Soon, 2007) Online here

  21. (Baur, 2008) Online here

  22. (Macilwain, 1998) Abstract here

  23. ibid

  24. (Global Warming Petition Project, 2008) Online here

  25. (Scientific American, 2005)

  26. (Prall, 2009) Online here. Prall gives statistics for activists and skeptics amongst the top 500 “most cited” authors. You must count the “most published” authors. Stats are based on Prall’s color coding. Carl Wunsch is both an activist and a skeptic because he appeared in The Great Global Warming Swindle (which he denounced).

  27. (Doran & Kendall Zimmerman, 2009) Online here.

  28. (Oreskes, 2004) Online here

  29. (Peiser, 2005) Online here

  30. (Lambert, 2005) Online here

  31. (Media Watch, 2006) Online here

  32. (Littlemore, 2007) Online here

  33. (Schulte, 2008) Abstract here

  34. (Lambert, 2007) Online here

  35. (Asher, 2007) Online here

  36. (Thomson Reuters) Online here

  37. (Bureau of Oceans and International Environmental and Scientific Affairs, 2007) Online here

  38. Annual reports online here.

  39. (CEI, 2006) Online here.

  40. (Achenbach, 2006) Online here.

  41. Cato’s pages for Patrick Michaels, and Penn & Teller. Penn & Teller’s appropriately titled Showtime Series.

  42. The First International Conference on Climate Change produced this document, the “Summary for Policymakers of the Report of the Nongovernmental International Panel on Climate Change” (Singer, 2008), which is notable because it summarized a “report” that didn’t exist. All of the contributors of the “summary” are included in Prall’s lists of climate change authors.

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