Climatologist James Hansen’s article “The Threat to the Planet” is featured on the front page of the July 13 New York Review of Books, which carries the label “Fiction Issue.” How appropriate. In his review of three alarmist books on global warming and of Al Gore’s documentary “An Inconvenient Truth,” Mr. Hansen stresses all kinds of catastrophic consequences of higher temperatures. Echoing the horror movie “The Day After Tomorrow,” He has sea level rising 20 feet by 2100, inundating most of Florida and a good many East Coast cities.By contrast, the U.N. panel of climate scientists, often claimed to represent a “consensus,” manages only about one-foot rise by 2100. Question: Is Mr. Hansen “out of the mainstream,” a closet “skeptic,” or even — to use Gorespeak — a “denier” of the consensus?
Mr. Hansen, you recall, is the NASA scientist who complained — most recently on CBS “60 Minutes” — of being “gagged,” “muzzled” and otherwise put upon by the Bush administration. He also accepted a quarter-million dollars from the Heinz Foundation of Teresa Heinz Kerry and campaigned for John Kerry and against George Bush in Iowa. No connection between these two events, of course. After all, it’s ketchup money, not oil money.
The main problems with Mr. Hansen, and others like him, are not the wild claims of coming disasters. No one in his right mind pays attention to these anyway. No, it is the fact that nowhere does he demonstrate that the current, rather modest warming trend is human-caused. He just assumes it: Temperatures are rising, and so is carbon dioxide in the atmosphere. Sorry, that’s not good enough. Not when he calls for far-reaching policies that would throttle energy use and the national economy.
Climate models are not evidence and correlations are not proof. The climate of the 20th century warmed sharply before 1940 when CO2 levels were low, and cooled until 1975 while CO2 rose rapidly. Clearly, natural climate fluctuations dominated. So how important is the human contribution to warming since 1975? There is no consensus: Scientific opinions vary from 0 percent up to 100 percent, with most somewhere in between. Tellingly, however, the patterns of warming do not agree with what is expected from the greenhouse effect of CO2.
There is a similar lack of consensus among economists. Some think that warming would be beneficial; others take the opposite view. But here we have relevant historical data. The planet (or at least the northern hemisphere) was much warmer in medieval times than today: Viking settlements in Greenland; no climate calamities; no inundations. The ice sheets survived the warming, and so did the polar bears.
The “Little Ice Age,” which followed the Medieval Warm Period and lasted till about 1850, was a real calamity, however: harvests failed, people starved, disease was rampant. So if cooling is bad, and if warming were also bad, why would our present climate just happen to be the best?