Often skeptics and deniers will criticize the so-called 97 percent consensus that anthropogenic global warming (AGW) is real, and predominantly related to our own activities such as increased greenhouse gas emissions and deforestation. I decided to look into this 97 percent a little deeper and find the truth. So here it is:
In May 2013, Cook, Nuccitelli et al published an article in Environmental Research Letters entitled “Quantifying the Consensus on Anthropogenic Global Warming in the Scientific Literature.” They reviewed only peer-reviewed scientific literature, examining a whopping 11,944 climate abstracts that pertained to global warming that were published between 1991 and 2011. They found that 66.4 percent of abstracts expressed no position on AGW, 32.6 percent endorsed it, 0.7 percent rejected it and 0.3 percent were uncertain about it. Among abstracts expressing a position on AGW, 97.1 percent endorsed it with about two percent rejecting it and one percent expressing uncertainty.
As I’ve mentioned to my patients many times, if 97 cardiologists recommended cholesterol-lowering medications as a way to reduce the risk of heart attack, stroke and death, and two cardiologists said don’t bother, and one said “I’m not sure,” I think most people would embrace the vast majority of expert opinion and consider lowering their cholesterol.
This all has to do with a concept in science called convergence of evidence, that many pieces from different sources converge toward the same conclusion. When it comes to AGW, we have many sources of evidence: pollen, tree rings, ice cores, corals, glacial and polar ice-cap melt, sea-level rise, ecological shifts, carbon dioxide increases, and the unprecedented rate of temperature increase. All of these sources of evidence converge toward the conclusion that our planet is warming and it’s primarily because of us.
Occasionally deniers will point out some anomaly in some particular data set, suggesting that’s enough reason to ignore all of the other lines of evidence as well. But if skeptics and deniers really want to turn the tables on the 97 percent consensus, they need to find flaws in all lines of supporting evidence, and also show a consistent convergence of evidence toward some different theory that explains the data even better.
So let’s look at the three percent who aren’t on board a bit more. Is there any suggestion of a contrary convergence of evidence on their part? In a paper published earlier this year in Theoretical and Applied Climatology, some of those same authors who published on the 97 percent consensus along with Rasmus Benestad and Katharine Hayhoe found that the three percent who didn’t embrace what the other 97 percent did had made “a number of methodological flaws and a pattern of common mistakes.” What’s more, these three percent didn’t have any convergence of evidence whatsoever. As Dana Nuccitelli put it in a commentary in the Guardian:
There is no cohesive, consistent alternative theory to human-caused global warming. Some blame global warming on the sun, others on orbital cycles of other planets, others on ocean cycles, and so on. There is a 97% expert consensus on a cohesive theory that’s overwhelmingly supported by the scientific evidence, but the 2–3% of papers that reject that consensus are all over the map, even contradicting each other. The one thing they seem to have in common is methodological flaws like cherry picking, curve fitting, ignoring inconvenient data, and disregarding known physics.
Most people who like to criticize the 97 percent consensus aren’t aware of these facts. Truth is, most deniers don’t even know where these numbers came from. But it’s easy to try to misdirect people from the truth by spewing out such rhetoric. For me, I’ll choose the 97 percent over those who can’t even agree among themselves about what they believe the alternative answer to be.
Even Albert Einstein faced such skepticism, and yet a century later both special and general relativity have survived. There was even a book published in 1931 entitled “100 Authors against Einstein.” When asked what he thought about the skepticism, Einstein said “Why 100? If I were wrong, one would have been enough.”