Consensus on Consensus

Barack Obama: 97% of scientists, including by the way some who originally disputed the data, have now put that to rest. They’ve acknowledged the planet is warming and human activity is contributing to it. John Oliver: A survey of thousands of scientific papers that took a position on climate change found that 97% endorsed the position that humans are causing global warming.

Bernie Sanders: Some 97% of scientists who have written in peer-reviewed journals say the following: climate change is real, it is significantly caused by human activity. David Cameron: 97% of scientists the world over have said that climate change is urgent, and man-made and must be addressed. John Cook: For over a decade, study after study has found that 97% of publishing climate scientists agree that humans are causing global warming. But what do the general public think? I’m here at the Brisbane city mall to find out.

John Cook: What percentage of climate scientists, do you think, agree that humans are causing global warming? Member of public: ninety-five percent. probably fifty percent seventy-five percent I think. Person Left: Eighty percent. Ya. Person Right: Eighty-five. John Cook: Would you like to know who was closer then? Person Left: I think I was closer. A hundred percent between five and ten percent Um, not a lot. Oh hang on, sorry, other way around. Ninety-five percent A split about fifty/fifty Person Right: I would say eighty percent Ninety-five percent Person Left: I would say fifty (sighs) half John Cook: There’s a huge gap between what many of the public think about the scientific consensus, and the actual 97% agreement among climate scientists. Why is there such a large consensus gap? One contributor is misinformation. Rick Santorum: The 97% figure that’s thrown around, the head of the U.

Richard Tol misrepresented a number of consensus studies, portraying non-expert groups as representative of the expert consensus

N. I.P.C. said that number was pulled out of thin air. John Christy: That 97% number, that’s been debunked in several studies. Richard Tol: This 97% is essentially pulled from thin air. Ted Cruz: The stat about the 97% of scientists is based on one discredited study. Bill Maher: …97% of all scientists believe… Rick Santorum: That’s a bogus number Bill Maher: It’s so not a bogus number Rick Santorum: It’s so a bogus number Bill Maher: Okay, yours is, mine is, yours is, mine is! From clips like this, you’d think there’s vigorous debate about whether scientists agree that humans are causing global warming. We’re often exposed to contradictory messages in the media. How do we see through the misinformation and get to the truth about consensus? I joined with scientists who authored seven of the key studies into the consensus on climate change.

When we looked collectively at the wide range of consensus studies, we found that the expert scientific consensus on human-caused global warming is between 90 to 100%. The higher the expertise in climate science, the stronger the agreement on human-caused global warming. When you get to climate scientists who have published peer-reviewed climate research, there’s 97% agreement. But the fact that consensus gets stronger with higher expertise is exploited by those looking to cast doubt on the consensus. They do this by selecting groups of scientists that have lower expertise in climate science to get a lower level of scientific agreement and argue that there is no consensus. Using non-experts to cast doubt on the expert consensus is a key characteristic of science denial known as the appeal to fake experts. This approach was employed by Richard Tol in a comment criticising the 97% consensus. Tol misrepresented a number of consensus studies, portraying non-expert groups as representative of the expert consensus.

The scientists who authored those studies were none too happy with how their research was misrepresented. But on the positive side, Tol’s misrepresentation of all those studies brought the authors of seven key studies together to publish a full view on the scientific consensus on climate change. Our paper established a consensus on the consensus being between 90 to 100% expert agreement on human-caused global warming, with a number of studies finding 97% consensus..