What Counts as Climate Consensus?

Oren Cass’s article “Who’s the Denier Now?” (May 1) condemns the misuse of scientific data in climate-change policy debates, but to support his position Cass misrepresents the findings in our survey of economists and cherry-picks survey data to suggest that “economists hold widely varying views” on the costs of climate change. In fact, we found a high level of consensus on the same survey questions Cass discusses: Only 6 percent thought that more research was needed before action should be taken on climate change or that it is not a serious problem; 89 percent thought that climate change will be a “very serious” or “somewhat serious” problem for the U.S. if it is not addressed; and 89 percent thought that climate impacts will have a net negative effect on the global economy by 2050. Seventy-eight percent of the economists expect climate change to reduce the growth rate of the global economy, and 77 percent think the U.S. should commit to reducing emissions regardless of other countries’ actions.

As Cass notes, uncertainty is inherent in estimating climate impacts. But while damages might end up being less serious than anticipated, they also might be more severe.

Among the world’s foremost economists with expertise on these issues, there is consensus that climate change poses a major risk to our economy and should be addressed.

Derek Sylvan & Peter Howard

New York University

Oren Cass responds: It is difficult to “mispresent” a study by providing direct quotations from the relevant results. I took statements tested by Sylvan & Howard (S&H) that approximated overstated claims of “consensus” and then provided readers with the exact survey language and the percentage of economists agreeing with each.

For instance, I quoted Senator Bernie Sanders asserting a 97 percent consensus among scientists that climate change “is already causing devastating problems around the world” and explained that surveys of scientists do not even ask this, while economists hold widely varying views. S&H report that 41 percent say that “climate change is already having a negative effect on the global economy.”

S&H’s claim of consensus requires them to combine disparate answers. For instance, they describe an 89 percent “consensus” from adding together the responses that the negative economic effect of climate change has already begun (41 percent), will begin by 2025 (22 percent), or will begin by 2050 (26 percent). This is like asking people whether they prefer apples, bananas, oranges, or pears and then reporting a 90 percent “consensus” for “apples, bananas, or oranges.”

Presumably, they designed their survey specifically to distinguish between economists who believe a negative economic effect has begun, will begin soon, or will not begin for decades because they recognized that those are meaningfully distinct answers representing different views. They cannot trumpet the subsequent diversity of responses as consensus by recombining the categories into “now or soon or later.”