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Article for Investigation 4.1: 1988

S.F. Forum on Global Warming Hears Heated Scientific Debate

By Charles Petit, The San Francisco Chronicle,
1989 December 7, page A18


Scientists differed sharply yesterday whether the greenhouse effect is already warming the planet—and a few doubted the widely believed forecasts of climate catastrophe in the next century.

At a meeting of the American Geophysical Union in San Francisco’s Civic Auditorium, there was a rare public confrontation between a prominent scientist warning that global warming is already under way and threatens to wreak havoc in the next century, and other researchers who say it is too early to tell.

It is a controversy certain to heat up as scientists measure the shifting chemistry of the atmosphere, tune computer models of the world’s ocean, clouds, and winds, and analyze unreliable temperature records from the last century.

James Hansen, director of the NASA Goddard Institute for Space Studies in New York, repeated the assertion he made to Congress a year ago that he is 99 percent certain that the globe will warm dramatically, by 3 to 9 degrees Fahrenheit, during the next century. This is a faster rise than any known in geologic history, and would make the Earth hotter than it has been in 100,000 years.

But a small band of researchers believe Hansen in particular, and many others, are making forecasts that go beyond the evidence.

Thomas R. Karl, of the National Oceanic and Atmospheric Administration research center in North Carolina, said Hansen’s main contention that warming has already begun is not backed up by temperature records going back to 1850.

Last year Karl said that when temperatures dating back to the turn of the century are studied, and corrected for generally warmer readings in industrial areas, there is no long-term trend leading upward.

Climatologist Tim P. Barnett of the Scripps Institute of Oceanography in San Diego joined Karl in the criticism. His graphs and plots suggest that natural oscillations in global temperature are so large that they would conceal any signal that the warming had already begun.

Barnett took a hard shot at Hansen’s use of global temperature averages as evidence for accuracy of computer predictions. Global averages, he said, are “an absolutely bogus concept . . . to be real blunt about it, to use Southern California surfer jargon, (use of) global averages sucks, guys.” Barnett told the morning meeting of several hundred climate experts.

Hansen responded that his own analysis of the same data used by Karl not only confirms a global warming, but suggests the United States has warmed by up to half a degree in the past century. He said Karl “made an embarrassing mistake” in not using the data correctly.

Hansen got powerful support from a mathematician’s detailed statistical analysis of variations in global temperatures for the past 100 years.

Statistically, the chances that the carbon dioxide is not causing warming are about 2 in 1 million, said David J. Thompson of the Mathematical Sciences Research Center at AT&T Bell Labs in New Jersey. “It looks like cause and effect to me,” he said.

Greenhouse doubter Barnett said that he shares Hansen’s view that the future does not look good. “Most scientists agree that if we put most of the stuff into the atmosphere (that is predicted), we will have a real climate problem . . . a climate regime that human civilization has never seen.”

The session moderator, H. Frank Eden of the Joint Oceanographic Institutions, said, “We may not agree that we can already see the warming, but most of us believe in the general idea of the greenhouse effect.”