“The 97 Percent”

I am not a fan of the term “denier” or “denial” when tossed around on the subject of climate change. In most cases it does not serve a constructive purpose. However, in describing a recent op-ed in the WSJ by Joe Bast and Prof Roy Spencer, it is difficult for me not to use the word.

Anyone who has first-hand with the field knows that the number of published, active researchers in the field who challenge the main findings on climate change1 is miniscule. It simply can’t be more than a few percent. And one is hard pressed to find a single professional scientific organization that doesn’t make a clear statement on the subject.

Even guys like Roy Spencer, when pushed hard enough, will admit that they are a minority voice. This is why I find articles like the WSJ piece completely baffling.  In the op-ed, Spencer and Bast challenge the claim that 97% of the climate scientists agree on the main points of global warming. But here’s their bait-and-switch: they don’t really offer an alternative number and they avoid saying exactly how wrong they think that figure is, leaving much to innuendo.

First a little history

The claim that “97% of all climate scientists agree…” comes from a series of studies: Naomi Oreskes performed a literature search, looking at abstracts from 928 papers matching the keywords “climate change”. Orskes found no papers contradicting the consensus findings, as described by the International Panel on Climate Change (IPCC). Doran & Zimmerman (2009) polled 10,000 earth scientists and found a broad consensus among all scientists, with 97% agreement among those actively publishing climate research.  Anderegg et al. (2010) reviewed publicly signed declarations supporting or rejecting human-caused global warming, and again found high consensus among climate experts.  Cook et al. (2013) performed a literature search, in a similar vein to Oreskes, and found that among papers addressing the question of anthropogenic climate change 97% affirmed the consensus position. Two other surveys of note find high levels of agreement (>85%), especially among experts, though not the 97% number: A survey by the American Meteorological Society (AMS) and one by Brey and Von Storch. We will discuss these shortly.

None of these surveys is perfect. All of them have certain strengths and weaknesses, but they are useful at illustrating to the public what those in the scientific community know: that people who outright deny a warming trend, who challenge the notion of an anthropogenic cause, and who consider the effects of the warming to be harmless represent a marginal view among the broad community of experts.

Picking Nits

Surveys and literature searches are inherently imperfect, so it’s easy to raise methodological objections. This is fine. Climate change is a complex subject and not easily reduced to a yes or no question. On this basis, I am inclined to agree that one should take the exact figure 97% with a grain of salt. But, questioning whether the number is 90% or 99% is not the same as doubting that there ultimately is broad agreement. And, this is where I find the op-ed to be deceptive and obfuscating. Not only do Spencer and Bast fail  to imply a lack of consensus on harmful, man made global warming, but most of their own sources contradict them. So what have they got?

Seriously, “the Oregon Petition”?

The thing that I find most shocking about the WSJ op-ed is the retreading of the infamous “Global Warming Petition Project” (aka the Oregon Petition). It’s bizarre that Spencer and Bast spend half of their article nitpicking the methodologies of surveys based on standard practices, and then they turn around to hang their hat on a petition that doesn’t follow any practices. If you are unfamiliar, here are few key problems with the petition:

(1) It’s a petition, not a survey. No attempt is made at selecting a representative sample and no effort is made to determine ratio of scientists who challenge global warming to those who don’t. (2) Their only standard for defining a “scientists” is the dubious requirement that one simply have a bachelors in science or engineering. Would you accept legal advice from a pre-law or have surgery performed by a guy with only an undergraduate? Then you shouldn’t take an undergrad in physics to be a serious authority on atmospheric physics. To wit, 31,000 people with a bachelors or more in science is less than 0.3% of the ~10 million (Americans alone) who have a bachelors in science. Even the 9,000 PhDs the survey boasts is small when you consider that ~30,000 new PhDs in science are awarded every year. (3) Most of the PhDs who signed the petition are in fields that have nothing to do with climate science.  The number of self-identified climatologists who sign the petition is 39, with maybe one or two thousand in related fields (if you want to be generous). I don’t know how anyone can say with a straight face “31,000 scientists support our petition. Of those, 39 actually study the subject matter relevant to the petition”. Peter Hadfield has a great video on youtube explaining what it means to be “an expert”.

We won’t even get in to issues with the tactics of the survey or the fact that the survey was at one point signed by Perry Mason, the Doctors from MASH, and even the Spice-girls.

The AMS Survey

The op-ed goes on to quote an American Meteorological Society survey (the paper can be found here). Say Bast and Spencer,”only 39.8%…said man made global warming is dangerous.” They must be hoping that their readers don’t actually bother to read the survey. In response to how harmful or beneficial global warming would be over the next 150 years, 38% respondents answered “very harmful” but they neglect to mention an additional 38% answered “somewhat harmful”. That’s 76% who believe the consequences of warming will range from “somewhat harmful” to “very harmful”. Even this understates the level of agreement because the 24% who believe that the consequences will be benign includes many AMS members who do not qualify as scientists or climate experts. Of the respondents, 38% do not have a PhD. Only around 23% of the respondents claim to publish primarily on the topic of climate science. In fact, the main finding of the survey is that climate consensus is much higher among those who actually have the relevant expertise.

Brey and Von Storch

Bast and Spencer go on to cite a survey by Brey and Von Storch. This is one of my favorite surveys on the topic. I happen to think that it paints a pretty accurate picture of the state of the field. It covers a wide range of topics. Rather than a simple “yes” or “no” choice, the questions are answered on a scale from 1 to 7. And, they have a good sample size and composition.

Ironically for Bast and Spencer, the level of consensus expressed in the Von Storch paper happens to be pretty strong and it agrees well with the levels of confidence expressed by the IPCC. Point-by-point, if you look at topics where there is high agreement in the survey, they correspond to findings that the IPCC attributes with “high confidence”. The points where there is little agreement in the survey correspond to findings that the IPCC cites as having “low confidence”.

Throughout their editorial, Bast and Spencer  have been focusing on the question of how many climate experts believe in “harmful, man-made global warming”.  For some reason they neglect to report the results of this survey on those very questions (gee, I wonder why?). Let’s look at the results:




Why I Don’t Like the “97% number”
Polls inevitably make oversimplifications and understate the complexity of the issues. The 97% number gives the impression of a monolithic “climate orthodoxy” that isn’t there. In reality, climate scientists hold a spectrum of views, and many subjects are still hotly debated. It is difficult to reduce everything to simple yes-no questions, and I am skeptical of the precision implied by using 2 significant digits in the 97% number. That said, there are certain key findings of climate science supported by so many data and so many lines of evidence that everyone in the community has moved on. Everyone, that is, but guys like Prof Spencer (although even Spencer concedes some amount of greenhouse warming).

But you don’t have to take my word for it

To any nonscientists who doubt the level of agreement among climate scientists: I challenge you to make a list of scientific institutions, pick a random sample and see for yourself how hard it is to find an active climatologist who does not believe the earth is warming (a few percent) or who doesn’t think humans are responsible for a good chunk of the last half-century warming (<10%) or  who thinks that the consequences will be benign (probably <10%). Pick a few journals and regularly read the articles (if you need help, recruit a scientist friend).  You will quickly see just how marginal your outlook is.

Can We Move On Now?

Policy makers and the public need to know that essentially no one in the climate science community questions the premise that world has warmed over the last century. Policy makers and the public need to know that the vast majority of the climate science community are convinced that more than half of the warming since the 1950s is driven by manmade causes. Policy makers and the public need to know that the vast majority of climate scientists feel that the implications of this man-made warming are likely to range from somewhat harmful to very harmful. Instead of peddling doubt and innuendo, Spencer and Bast should actually help to make constructive improvements to the process of polling the community. Ultimately, if they want to nitpick over the exact percentage that constitutes a “vast majority” of climate scientists, more power to them. But, if they’re trying suggest that there isn’t any majority among climate scientists on these three key points, then they’re just being counterfactual.


1. For the entirety of this article, I will define “the main findings” of science on climate change as being (1) the earth is warming (2) most of the warming since the mid-20th century is and will continue to be driven by man-made causes (primarily greenhouse gases) and (3) that the consequences of continued warming will incur economic and human costs.



  1. Branden Hall

    One chestnut I’ve seen bandied about it how, in the 1970s, scientists thought we were about to go through another ice age. Do you know if that opinion as widely held as the current position on climate change?

    • Matt

      Hey Branden, thanks for the comment. The answer to your question is “yes and no”. In the 70s, there was a lot that was yet unknown about the earth’s climate. There were indeed some concerns that aerosols from pollutants would cool the earth (Rasool and Schneider are two of the big names). These views were more subtle than the ones you’ve probably seen on the web (there is a really over-quoted Time Magazine article on the subject), but there were real concerns. On the other hand, there were a larger number of scientists who felt that the warming from CO2 would eventually overpower the cooling from aerosols (even Schneider changed his opinion by the late 70s). The majority of the publications in that decade leaned towards warming, though only slightly.

      This whole story underscores the significance and relevance of having a consensus. In the 1970s, the community was *not* in agreement, and if you look at the climate reports at the time they admit as much. In the following 40 years, after many important studies, papers, and measurements, the evidence was sufficient to bring everyone into agreement on the key points. There are still lot’s of unresolved issues and contentious points, but the notion that increased CO2 is warming and will continue to warm the planet (likley by more than 2 degrees C) is *not* one of them.

      An interesting discussion on the subject can be found here:

      And actually, Spencer Weart’s whole online book on the history of climate science (http://www.aip.org/history/climate/index.htm) is worth checking out.

      Hope that was helpful.

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