Fact Checking The Claim Of 97% Consensus On Anthropogenic Climate Change


University of Houston Energy Fellows

BY Earl J. Ritchie, Lecturer, Department of Construction Management
(Photo by Fabrice BEAUCHENE)

The claim that there is a 97% consensus among scientists that humans are the cause of global warming is widely made in climate change literature and by political figures.

The 97% figure has been disputed and vigorously defended, with emotional arguments and counterarguments published in a number of papers. Although the degree of consensus is only one of several arguments for anthropogenic climate change – the statements of professional societies and evidence presented in reports from the Intergovernmental Panel on Climate Change are others – there is data to suggest that support is lower. In this post, I attempt to determine whether the 97% consensus is fact or fiction.

The 97% number was popularized by two articles, the first by Naomi Oreskes, now Professor of Science History and Affiliated Professor of Earth and Planetary Sciences at Harvard University, and the second by a group of authors led by John Cook, the Climate Communication Fellow for the Global Change Institute at The University of Queensland. Both papers were based on analyses of earlier publications. Other analyses and surveys arrive at different, often lower, numbers depending in part on how support for the concept was defined and on the population surveyed.

This public discussion was started by Oreskes’ brief 2004 article,which included an analysis of 928 papers containing the keywords “global climate change.” The article says “none of the papers disagreed with the consensus position” of anthropogenic global warming. Although this article makes no claim to a specific number, it is routinely described as indicating 100% agreement and used as support for the 97% figure.

In a 2007 book chapter, Oreskes infers that the lack of expressed dissent “demonstrates that any remaining professional dissent is now exceedingly minor.” The chapter revealed that there were about 235 papers in the 2004 article, or 25%, that endorsed the position. An additional 50% were interpreted to have implicitly endorsed, primarily on the basis that they discussed evaluation of impacts. Authors addressing impacts might believe that the Earth is warming without believing it is anthropogenic. In the article, Oreskes said some authors she counted “might believe that current climate change is natural.” It is impossible to tell from this analysis how many actually believed it. On that basis, I find that this study does not support the 97% number.

The most influential and most debated article was the 2013 paperby Cook, et al., which popularized the 97% figure. The authors used methodology similar to Oreskes but based their analysis on abstracts rather than full content. I do not intend to reopen the debate over this paper. Instead, let’s consider it along with some of the numerous other surveys available.

Reviews of published surveys were published in 2016 by Cook and his collaborators and by Richard S. J. Tol, Professor of Economics at the University of Sussex. The 2016 Cook paper, which reviews 14 published analyses and includes among its authors Oreskes and several authors of the papers shown in the chart below, concludes that the scientific consensus “is robust, with a range of 90%–100% depending on the exact question, timing and sampling methodology.” The chart shows the post-2000 opinions summarized in Table 1 of the paper. Dates given are those of the survey, not the publication date. I’ve added a 2016 survey of meteorologists from George Mason University and omitted the Oreskes article.

The classification of publishing and non-publishing is that used by Cook and his collaborators. These categories are intended to be measures of how active the scientists in the sample analyzed have been in writing peer-reviewed articles on climate change. Because of different methodology, that information is not available in all of the surveys. The categorization should be considered an approximation. The chart shows that over half the surveys in the publishing category and all the surveys in the non-publishing category are below 97%.

Scientists Opinions of Human-Caused Global Warming

Cook is careful to describe his 2013 study results as being based on “climate experts.” Political figures and the popular press are not so careful. President Obama and Secretary of State John Kerry have repeatedly characterized it as 97% of scientists. Kerry has gone so far as to say that “97 percent of peer-reviewed climate studies confirm that climate change is happening and that human activity is largely responsible.” This is patently wrong, since the Cook study and others showed that the majority of papers take no position. One does not expect nuance in political speeches, and the authors of scientific papers cannot be held responsible for the statements of politicians and the media.

Given these results, it is clear that support among scientists for human-caused climate change is below 97%. Most studies including specialties other than climatologists find support in the range of 80% to 90%. The 97% consensus of scientists, when used without limitation to climate scientists, is false.

In the strict sense, the 97% consensus is false, even when limited to climate scientists. The 2016 Cook review found the consensus to be “shared by 90%–100% of publishing climate scientists.” One survey found it to be 84%. Continuing to claim 97% support is deceptive. I find the 97% consensus of climate scientists to be overstated.

An important consideration in this discussion is that we are attempting to define a single number to represent a range of opinions which have many nuances. To begin with, as Oreskes says, “often it is challenging to determine exactly what the authors of the paper[s] do think about global climate change.” In addition, published surveys vary in methodology. They do not ask the same questions in the same format, are collected by different sampling methods, and are rated by different individuals who may have biases. These issues are much discussed in the literature on climate change, including in the articles discussed here.

The range of opinions and the many factors affecting belief in anthropogenic climate change cannot be covered here. The variety of opinion can be illustrated by one graph from the 2013 repeat of the Bray and von Storch survey showing the degree of belief that recent or future climate change is due to or will be caused by human activity. A value of 1 indicates not convinced and a value of 7 is very much convinced. The top three values add to 81%, roughly in the range of several other surveys.

A survey of the perceptions of climate scientists 2013 (Graph by Dennis Bray & Hans von Storch)

Even though belief is clearly below 97%, support over 80% is strong consensus. Would a lower level of consensus convince anyone concerned about anthropogenic global warming to abandon their views and advocate unrestricted burning of fossil fuels? I think not. Even the 2016 Cook paper says “From a broader perspective, it doesn’t matter if the consensus number is 90% or 100%.”

Despite the difficulty in defining a precise number and the opinion that the exact number is not important, 97% continues to be widely publicized and defended. One might ask why 97% is important. Perhaps it’s because 97% has marketing value. It sounds precise and says that only 3% disagree. By implication, that small number who disagree must be out of the mainstream: cranks, chronic naysayers, or shills of the fossil fuel industry. They are frequently described as a “tiny minority.” It’s not as easy to discount dissenters if the number is 10 or 15 percent.

The conclusions of the IPCC are the other most often cited support for anthropogenic climate change. These conclusions are consensus results of a committee with thousands of contributors. Although this is often viewed as a monolithic conclusion, the nature of committee processes makes it virtually certain that there are varying degrees of agreement, similar to what was shown in the Bray and von Storch survey. The Union of Concerned Scientists says of the IPCC process “it would be clearly unrealistic to aim for unanimous agreement on every aspect of the report.” Perhaps this is a subject for another day.

Earl J. Ritchie is a retired energy executive and teaches a course on the oil and gas industry at the University of Houston. He has 35 years’ experience in the industry. He started as a geophysicist with Mobil Oil and subsequently worked in a variety of management and technical positions with several independent exploration and production companies. Ritchie retired as Vice President and General Manager of the offshore division of EOG Resources in 2007. Prior to his experience in the oil industry, he served at the US Air Force Special Weapons Center, providing geologic and geophysical support to nuclear research activities.

August 24, 2019 | 8 Comments »

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8 Comments / 8 Comments

  1. @ Bear Klein: All this is true, Bear. The failure of China to do anything about the massive pollution there is awful. Ditto India and other “developing countries” and emerging markets. This massive pollution is one of several dozen reasons why I think the U.S. should embargoall trade with China. But of course that won’t happen.

    It is just common sense that cars and power plants that emit a lot of carbon into the atmosphere are going to accelerate global warming, since carbon dioxide is a known insulating gas. Few if any scientists deny this.

    While it is certainly true that natural forces have been changing the climate for over a billion years, this in no way means that present-day human activity is not accelerating the process. Also, climate change today will cause more damage to humans than in previous centuries and millennia, because there are so many more people today, and they are so much more interdependant than in the past. Also, people are more “spoiled” today, which means they are less likely to be stoic if climate change makes life more uncomfortable. Our ancestors put up with climate change and many worse disasters without losing their social cohesion and morale. I doubt if moderns will do the same. Riots, disorders, etc. will be common if the weather becomes less comfortable.

    While the experts emphasize the value of tree-planting in arid places, and I won’t challenge their opinion that that is where it will do the most good, I think it would be very helpful everywhere on the planet. It’s just common sense. Trees absorb carbon dioxide, which is one of the major causes of warming. They produce oxygen, which we need to breath. Everyone who has ever walked in the woods or even sat under a tree knows it is much cooler there than on asphalt road or in an urban area with lots of concrete and asphalt. Even in urban areas, such as the one where I live, breezes from surrounding wooded areas cool the air to some degree.

    The Paris accords do not require a ban on fossil fuels, as is commonly believed. Only more widespread and systematic use of carbon-capture techniques that already exist. This could be done at a manageable cost. But the non-cooperation of many countries with these recommendations means they probably won’t be. While it is true that the United States has done a good job of containing carbon emissions in recent years, President Trump’s rejection of the carbon accords does nothing to discourage the “developing” industrial nations from ignoring them.

    The basic problem is that humans lack common sense. If they had more of that, the global warming problem could easily be solved. As it is, this problem and a thousand other, even more serious,, environmental problems will not be solved.

  2. The fact that Trump has an opinion about something does not mean that that opinion is relevant to Israel. And just that the MSM has an opinion about something, doesn’t make it relevant to Israel.

    Just because the MSM has reported something doesn’t mean that it must be a hoax. For example, the MSM has reported that U.S. Astronauts have gone to the moon, and that the United States has sent space probes to Mars, Sattern, Jupiter, and even Pluto. Does that mean that the Hare Krishna sect is right when it says all this is a hoax? From time to time the MSM has published photographs taken from the moon or orbiting spacecraft showing the earth to be spherical. Does that mean we must support the claims of the Flat Earth Society (which does exist, and even has some members with scientific backgrounds) that these photographs are fake?

  3. The climate of the earth is changing. The earth is billions of years old. The climate has had always had major changes. The question is how much of it is man made due to carbon omissions.

    Clearly too much carbon is not good for all sorts of things like breathing for example. Some of the past proposals like the Paris Climate Treaty would have had a massive negative economic impact on places like the USA but allowed major polluters like India and China to keep polluting. The USA’s carbon output actually has decreased in recent years.

    The only thing I have read that the actually would cool the temperature and reduce the C02 output are the two studies I cited above to plant massive amount of trees in Sub-Saharan Africa and Australia. Instead of pretending that all fossil fuels are no longer going to be used in 20 years or so, I think it logically to get behind the mass planting of the trees per the studies.

    Nothing wrong with using clean energy to generate electricity or power vehicles in fact it is a positive development but this in itself not going to clean the planet. Just ask anyone who has been to China about the air.

  4. When I averaged out on my calculator the percentage of climate change affirmers in the nine studies of published scientific authors , they come to 93.11 per cent climate change affirmers. This is not a very significant difference from 97%. And four of the studies of the opinions of scientists who published articles about climate change did find that 97% of them did support the climate change hypothesis.

    There is nothing in this article that undermines the climate change hypothesis. The author does not even claim to have any personal knowledge about climate change himself. How could this article possibly be of any interest to anyone who cares about Israel?

  5. Ted, the only “scientists” who seem to be climate-change deniers are people who worked in the energy industries. As far as I can learn, none of them are meteorologists–the scientific profession that specializes in analizing and predicting weather and climate trends. This is the only profession which has expertise in climate change patterns. How many meteorologists think the climate change-global warming hypothesis is false? I don’t know of any.

    Obviously, people whose background is in petoleum or nuclear engineering are going to defend these industries. That doesn’t mean they know anything about climate matters.

  6. What I liked about this article is that it delves in the “97% concensus” and shows it’s oddness. For my part I don’t care if its 97% concensus of 80%.. I have bigger issues.

    I accept that the climate is warming and that man has played a role in that. But the real question is what percentage of the temperature rise is caused by increased carbon component in the air. No one discusses that. I recall reading that historically temperatures rose before carbon content did, yet people argue that the increased carbon content caused the temp to increase. not so.

    There may be other factors that cause them temperatures to rise. No one raises this question.

    The only way to get grant money to do a study is to say you are a supporter. This limitation should be lifted. The only place that skeptics can get financing is to go to EXXON etc. In the era of PC, god help you if you challenge the concensus.

    I have not seen a study that argues that the proposals put forward for solving the problem will work.

    I could go on and one.

  7. @ Adam Dalgliesh:
    I understand where you are coming from. What has this got to do with Israel or Jews. Valid question , so let me try to answer.

    Trump has been supporting Israel in every way possible. He has our back, you might say. Similarly I support Trump and have never said a negative word about him. You might say, I have his back. I don’t stand in judgement of any of his policies. I just have his back. Thus since he is a skeptic of climate change, I support him.

    But beyond that I have read many articles written by skeptics of climate change, and I find their arguments convincing. I know you and others disagree with the skeptics.

    I find the subject very interesting. When ever I post an article , many people read it showing me there is great interest. As I said before, we are subject to so many attemps to brainwash us that I don’t trust anything coming from the left. Better to question everything e.g. Trump colluded with the Russians, Trump is a racist, Kavanaugh is a rapist, Hillary didn’t do anything wrong, NAFTA is good for America, diversity is our strength. open borders are good. Islam is a religion of peace,and on and on.

    Also I often post topics of general interest or videos of interest like gymnastics and singing. But the only thing you have ever questioned me on was the attention I give to climate skepticism.

    If the oceans are going to rise 10 feet in 12 years or 100, this is something that should interest everyone, even Zionists.

  8. Again, I just don’t understand why a pro-Israel site should be pushing this issue. It is irrelevant to Israel’s present-day problems, and pushing it does nothing to improve Israel’s image–which desperately needs improvement.

    Most scientists who have made and published detailed studies studies of climate-related statistics believe that climate change is likely to have some significant negative impacts on human health by about 2100, if the current warming trend continues. However, the far more urgent problems facing Israel right now make it unlikely that Israel will even exist in 2100, and even make it uncertain whether Judaism will exist as a faith, and whether Jews will exist as a recognizable, distinct people, unless vigorous efforts begin right now to address Israel’s problems. So far, the Israeli government hasnot done this.

    I think that patriotic Jews need to prioritize Israel’s struggle for survival as their main focus, and leave alone issues that are not connected with this struggle, and that only serve to distract Jews from this priority issue .

    Let us suppose that it was possible to prove beyond reasonable doubt that climate change is not real, and or it is harmless. I don’t think anyone can or has proved that. But let’s just suppose. Would be of any benefit to Israel? Absolutely not! Or let us suppose that someone could prove beyond reasonable doubt that climate change is happening and will result in some sort of disaster for the human race. Would proving this help Israel? Probably not, unless it were proved that a climate-based disaster was going to strike within a few years in the Mideast. As far as I know, no scientific study of Mideast climate predicts this.

    So wise advocates of Israel’s security and acceptance in the family of nations would do well to avoid this isse and concentrate on Israel-relevant ones.