Is the 97% claim fallacious?

Activists, politicians and advocates who are passionate about global warming often use the claim that “97% of scientists” support their views to end debates. A typical example is a tweet from President Obama in May of 2014: “Ninety-seven percent of scientists agree: #climate change is real, man-made and dangerous.”

Leaving aside the quality of this claim as a statement of fact, isn’t this a logical fallacy when used as a counter-argument? Below, I offer an example of a typical exchange I’ve had with global warming advocates. (As with all such examples, I should point out in advance that it is a bit of a straw man.) I then make my case for why the argument is a fallacy and of what type. Please let me know what you think of my assessment as an expert in logical fallacies.

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ME: I’m skeptical of the claims I keep hearing from environmental activists about global warming. I mean, how can we possibly know what the temperature will be in 100 years with technology changing so rapidly? And if it takes satellites, ocean monitors and other sophisticated technology to get accurate global temperature readings today, how can we possibly know what the correct global temperature was 100 years ago? Also, if there’s warming, how do we know it isn’t primarily natural variation? We’ve had many warm periods and cold periods in earth’s history.

ADVOCATE: All you need to know is that 97% of scientists agree that global warming is real, caused by humans and will be catastrophic. Denying that truth is no different than denying the Holocaust.

ME: Ouch. I’m of Jewish heritage and had relatives who died in the Holocaust. I guess I’ll shut up now.

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Besides the appeal to emotion/abusive analogy, which I obviously added for effect, I submit that the Advocate in my scenario has committed a variant of two known fallacies: the argumentum ad numerum and argumentum ad verecundiam. Overall, his statement is a fallacy because he has not articulated a response to any of my questions. Rather, he has sidestepped the questions and attempted to end the debate with an appeal to the large number of scientists who agree with his view (ad numerum). By using scientists, he has also made an appeal to authority, which is supposed to shame me, a layman, into silence (ad verecundiam).

Finally, and this is a bit more tenuous, he has cited a statistic that may – in and of itself – contain an ad verecundiam. I understand that the appeal to authority may also be defined as an appeal to false authority, which works like this: I use the opinion of experts to shut down an argument against my position, but I fail to mention that a significant portion of my experts don’t specialize in the field about which the statement is made.

In this case, I have read that many of the scientists who comprise the “97% percent” have no expertise in the impact of greenhouse gases on global temperature – i.e. the expertise required to make the statement attributed to them – with any degree of authority. They only do research in their specific field (e.g. ice flows, cloud formations) and simply responded to an opinion survey or signed a petition from an activist group.

Please note: I make no claim that what I have read is the truth. I only ask that you assume it is true for the sake of this discussion.

Let me know what you think of all of this.