HACE SÓLO TREINTA AÑOS, la histeria consistía en tirarse de los pelos porque todos los científicos afirmaban de forma unánime que el planeta se estaba congelando a pasos agigantados, como recuerda George Will:

Science magazine (Dec. 10, 1976) warned of "extensive Northern Hemisphere glaciation." Science Digest (February 1973) reported that "the world's climatologists are agreed" that we must "prepare for the next ice age." The Christian Science Monitor ("Warning: Earth's Climate is Changing Faster Than Even Experts Expect," Aug. 27, 1974) reported that glaciers "have begun to advance," "growing seasons in England and Scandinavia are getting shorter" and "the North Atlantic is cooling down about as fast as an ocean can cool." Newsweek agreed ("The Cooling World," April 28, 1975) that meteorologists "are almost unanimous" that catastrophic famines might result from the global cooling that the New York Times (Sept. 14, 1975) said "may mark the return to another ice age." The Times (May 21, 1975) also said "a major cooling of the climate is widely considered inevitable" now that it is "well established" that the Northern Hemisphere's climate "has been getting cooler since about 1950."

In fact, the Earth is always experiencing either warming or cooling. But suppose the scientists and their journalistic conduits, who today say they were so spectacularly wrong so recently, are now correct. Suppose the Earth is warming and suppose the warming is caused by human activity. Are we sure there will be proportionate benefits from whatever climate change can be purchased at the cost of slowing economic growth and spending trillions? Are we sure the consequences of climate change -- remember, a thick sheet of ice once covered the Midwest -- must be bad? Or has the science-journalism complex decided that debate about these questions, too, is "over"?