The consensus among research scientists on anthropogenic global warming has grown to 100%, based on a review of 11,602 peer-reviewed articles on “climate change” and “global warming” published in the first 7 months of 2019.
We can date the beginning of consensus-building on anthropogenic global warming (AGW) to Manabe and Wetherald (1967). Their pioneering computer modeling showed that doubling atmospheric CO2 would raise global temperature by about 2°C, lower than the present best estimate but not by much. Their finding convinced the late Wallace Broecker that what he named “global warming” was “a thing to worry about” (Broecker, 1975; Weart, 2009).
As computer modeling steadily improved and global temperatures began their erratic but inexorable climb in the 1970s, a consensus grew first among climate scientists and then more broadly that AGW was true and indeed worrisome. Governments became concerned about the damaging potential of AGW, as reflected in the objective of the first United Nations Framework Convention on Climate Change, held in Rio in June 1992: “To achieve . . . stabilization of greenhouse gas concentrations in the atmosphere at a level that would prevent dangerous anthropogenic interference with the climate system” (United Nations, 1992, p. 4).
Because the use of fossil fuels has become so embedded in the world economy, it was clear that “stabilizing” greenhouse gases might require large-scale government intervention and regulation, anathema to some, including some scientists. This recognition gave rise to the repeated claim of global warming denialists: “There’s no consensus.”
Consider as examples two statements 20 years apart from Richard Lindzen of MIT. In 1992, he published an article titled, “Global Warming: The Origin and Nature of the Alleged Scientific Consensus” (Lindzen, 1992). It appeared in Regulation, a non–peer-reviewed periodical from the Cato Institute, a libertarian “think-tank.” The article began, “Many aspects of the catastrophic scenario have already been largely discounted by the scientific community [and] fears of massive sea level increases have been steadily reduced by orders of magnitude” (p. 87). In 2012, Lindzen and 15 coauthors published a letter to the Wall Street Journal titled, “No Need to Panic about Global Warming” (Lindzen, 2012). It opened with this paragraph:
A candidate for public office in any contemporary democracy may have to consider what, if anything, to do about “global warming.” Candidates should understand that the oft-repeated claim that nearly all scientists demand that something dramatic be done to stop global warming is not true. In fact, a large and growing number of distinguished scientists and engineers do not agree that drastic actions on global warming are needed.
The signatories included not only Lindzen but also a former astronaut and senator, the co-founder of the Journal of Forecasting, the President of the World Federation of Scientists, and a member of both the National Academy of Engineering and the National Academy of Sciences. This impressive list seemed to show not only that there was no consensus on AGW, but that distinguished scientists thought it might well be false. However, Lindzen was the only one of the 16 who had done climate research.
Scholars responded to the controversy by surveying the opinion of scientists. The results of eight such studies conducted between 2009 and 2015 showed a consensus on AGW ranging from 83.5% to 97% (Cook et al., 2016). But given the ingrained caution of scientists and their reluctance to affirm findings outside their own field, opinion surveys are likely to underestimate the consensus. Moreover, as shown by the controversy over continental drift, even a near-unanimous consensus among scientists can turn out to be wrong. If we look back at the early decades of continental drift, however, we find that there was little peer-reviewed evidence for or against the theory. As a result, early articles on continental drift contained much more opinion than evidence. Thus, we could say that although scientists turned out to be wrong about continental drift, the peer-reviewed literature was not wrong, only thin and inconclusive. This affirms that the most reliable way to gauge a consensus among scientists is to turn to the peer-reviewed literature and the evidence therein. This method also has the advantage of directly showing how likely a theory is to be true.