No Consensus on Consensus:
Logic & Rhetoric — By Joe Carter on December 4, 2006 at 12:35 am
How Not to Argue (Part III)
[Note: This is the third entry in the “How Not to Argue” series.]
“The question of what to do about climate change is also still open,” wrote Naomi Oreskes in a 2004 article in the journal Science. “But there is a scientific consensus on the reality of anthropogenic climate change. Climate scientists have repeatedly tried to make this clear. It is time for the rest of us to listen.” Many people will nod in agreement with Oreskes dogamatic assertion while others will express vehemently disagree. For example, Richard Lindzen, a professor of Atmospheric Science at MIT, says, “Al Gore is wrong. There’s no ‘consensus’ on global warming.”
While the question of whether climate change is anthropogenic is certainly worthy of discussion, I think the debate illuminates an underlying premise that is often ignored and unchallenged. The unexamined assumption is that if there is a consensus among relevant scientific experts then we must defer to their purportedly informed opinion in making policy decisions.
Pondering this question raises two related queries: (a) Should we automatically defer to the consensus opinion when making policy decisions? and (b) Why are the opinions of scientists treated with more deference than other “experts”?
Let’s start with the second question. As the global warming debate has shown, the claim that the scientific community has reached a consensus is often used as the primary basis for advocating for changes in public policy. But what makes scientists a special class of experts? Why don’t we defer to the “consensus” opinion of, say, economists, on policy matters?
After all, there are, as economist Robert Whaples shows in a recent study, a few issues where economists have reached a consensus*:
–87.5 percent agree that “the U.S. should eliminate remaining tariffs and other barriers to trade.”
–85.2 percent agree that “the U.S. should eliminate agricultural subsidies.”
–77.2 percent agree that “the best way to deal with Social Security’s long-term funding gap is to increase the normal retirement age.”
–67.1 percent agree that “parents should be given educational vouchers which can be used at government-run or privately-run schools.”
–90.1 percent disagree with the position that “the U.S. should restrict employers from outsourcing work to foreign countries.”
The methodology of economists is arguably as reliable as that of climatologists. In fact, I would contend that as a field of study, economics has a broader range of reliable data than does the climate sciences. Should we defer to economists then when they reach a consensus? Should politicians base decisions about education vouchers or tariffs on the consensus of these experts?
Most people would argue that it would be absurd to automatically defer to an opinion simply because a majority of economists agree. So why do we show such deference to scientists? Should their opinions carry more weight when it comes to establishing policy?
(Before you answer, consider that just thirty years ago there was a proposal to melt the Arctic ice cap because the “consensus” among scientific experts was that global cooling was leading to a new Ice Age. What was once considered a solution is now considered one of the dire consequences of global warming.)
Lest I be accused of having a pro-economist/anti-scientist bias, let me clarify that my point is not that consensus of scientists is irrelevant to political arguments but rather that appealing to consensus is insufficient for almost all arguments.
The fact that many people agree on something does not imply that what they agree on is true, whether the issue is climatology or farm subsidies. An appeal to consensus is merely a form of the argumentum ad populum fallacy (appeal to the majority). The status of the fallacy doesn’t change just because the members of the majority all have Ph.Ds. If you want to establish a consensus for your argument, you have to do more than appeal to a consensus.
Note: There are circumstances when an appeal to the majority is not an ad populum fallacy. One example is when people, whether experts or not, are in a position to determine the truth by forming a consensus. For example, the claim, “Most people in America think it is polite to shake hands with someone as a greeting; therefore, it is polite for people in America to shake hands when greeting” would not be fallacious.
* HT: Greg Mankiw’s Blog