Apr 8, 2016 by


The overwhelming majority of climate scientists — over 97 percent — understand that humans are the primary cause of climate change. This is one of the central facts about human-caused climate change that any climate communicator needs to keep repeating, for several reasons.

First, it’s true, as Politifact detailed on Monday. The scientific literature is clear on this.

Second, the ongoing disinformation campaign funded by the fossil fuel industry (together with false balance by the media) has left the public with the impression that there is considerable scientific debate on a subject where there isn’t.


When people are informed about the reality of the overwhelming consensus they naturally are more inclined to want to take action, as social science research has shown.

Let’s briefly explore the various ways to express the consensus, since some are more accurate than others. On March 24, U.S. Rep. Don Beyer (D-VA) wrote on his website, “Over 97 percent of the scientific community … believe that humans are contributing to climate change.”

PolitifactMostlyTruePolitifact Virginia rated this “Mostly True” on Monday. Politifact correctly notes that “The studies Beyer and others cite do not reflect the scientific community at large.” So they conclude “Beyer’s statement is credible but needs elaboration. We rate it Mostly True.”

It’s true that when you cite this statistic it is best to use “climate scientists” and not “scientists.” You can also use “peer-reviewed climate research” or “climate experts.”

As an aside, if you or child has a serious pancreas problem, I don’t think you’re going to be terribly interested what your cardiologist thinks, let alone your dentist. Similarly, it’s what climate scientists understand and what they can demonstrate in the peer-reviewed literature that we should care about.

Skeptical Science reviews the literature here. As environmental scientist Dana Nuccitelli explained in 2014, “Three distinct studies using four different methods have independently shown that the expert consensus on human-caused global warming is 97 ± 1%. The result is the same whether we ask the experts’ opinions, look at their public reports and statements, or examine their peer-reviewed science.”

Both Beyer and Politifact get a little sidetracked by looking at the out-of-date statement on NASA’s website: “Multiple studies published in peer-reviewed scientific journals show that 97 percent or more of actively publishing climate scientists agree: Climate-warming trends over the past century are very likely due to human activities. In addition, most of the leading scientific organizations worldwide have issued public statements endorsing this position.”

The NASA statement is based on the 2007 (!) assessment of the scientific literature by the Intergovernmental Panel on Climate Change, where, as NASA notes, the IPCC defines “very likely” as meaning “greater than 90 percent probability of occurrence.”

The thing is, by 2013, the IPCC’s summary of the science — which are notoriously conservative in part because they require line-by-line approval by every major country in the world — concluded. “It is extremely likely that human influence has been the dominant cause of the observed warming since the mid-20th century.”

The IPCC defines “extremely likely” as 95 to 100 percent certainty. That is comparable to the confidence the medical and public health community have that cigarettes are dangerous to your health.

It’s worth noting that the IPCC immediately states:

The best estimate of the human-induced contribution to warming is similar to the observed warming over this period.

That is, the best estimate by scientists is that humans are responsible for all of the warming we have suffered since 1950. Again, every major government in the world signed off on this finding — and yet the public, as well as media and opinion makers, are equally uninformed about this fact.

And so the second half of Beyer’s statement — the 97 percent “believe that humans are contributing to climate change” — is just way too weak, a point Politifact entirely glosses over. Indeed, it would be difficult to find any legitimate scientist — let alone one that had published on some aspect of climate change — who believed humans are not “contributing” to climate change.

The scientific literature — and the assessment of the literature unanimously embraced by the world’s governments — make clear that the overwhelming majority of climate scientists — over 97 percent — understand that humans are the primary cause of climate change.

If you want to be more specific, you can say “… understand that humans are the primary cause of global warming since 1950.” To keep it short but still accurate, you could say “over 97 percent of climate scientists understand that humans are causing climate change.”

I think “understand” is much better than “believe” since we are talking about a scientific fact here. Another good phrase is “have concluded.” The world’s largest general scientific society, the American Association for the Advancement of Science, put it this way in their blunt, must-read “What We Know” report: “Climate scientists agree: climate change is happening here and now. Based on well-established evidence, about 97% of climate scientists have concluded that human-caused climate change is happening.”

Finally, how confident are climate scientists of this conclusion?

“The science linking human activities to climate change is analogous to the science linking smoking to lung and cardiovascular diseases,” explains the AAAS. “Physicians, cardiovascular scientists, public health experts and others all agree smoking causes cancer. And this consensus among the health community has convinced most Americans that the health risks from smoking are real. A similar consensus now exists among climate scientists, a consensus that maintains climate change is happening, and human activity is the cause.”

We are as certain that humans are responsible for recent climate change as we are that cigarettes are dangerous to your health.

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