Global Warming Is a Hot Topic at White House

With a wide swath of the nation caught in the enervating grip of a deadly summer heat wave, President Clinton and Vice President Al Gore have seized on the attention it has generated to warn of the dangers of global warming.

“As you can see from this sweltering heat, the climate of our country and our globe is changing,” Clinton said Monday during an appearance in sweltering New Orleans.

But the science of global warming, the term attached to the notion that the Earth’s temperature is increasing because of the greenhouse effect, is much more complicated than that, as scientists, including government experts, have taken pains to emphasize.

It is unlikely that any one event can be attributed to global warming, they say, even though a trend to which it contributes--in this case record-setting high temperatures around the globe month after month--is said to prove that the world’s climate is getting warmer.

“Global warming is a relatively small change from year to year, but it is always pushing in one direction,” said Kevin Trenberth, one of the government’s leading researchers studying climate change around the world. “A lot of what we’re seeing at the moment is the kind of extremes we expect from global warming.”

Several recent climate trends have fueled the debate over global warming.

For each of the first six months of 1998, the mean global temperature was warmer than it was during the corresponding month in 1997. The monthly trend was topped off in June, when global surface temperatures were, on average, 1 degree warmer than the long-term mean temperature for the month, according to records kept since 1880 by the National Oceanic and Atmospheric Administration.

But critics of the global warming theory say measurements taken anywhere from 5,000 to 30,000 feet above the Earth--which, some say, show little recent change or perhaps even a cooling trend--are more meaningful.

In addition to the temperature increase at the Earth’s surface, drought in Florida contributed to the devastating fires there over the last several weeks, and torrential downpours produced unusually fierce flood torrents in the northeastern United States.

It is unclear whether these events are related to global warming.

Warmer temperatures may have pushed back the start of the summer rainy season in Florida, scientists say, and thus induced greater evaporation from the surface of the ocean, lifting more moisture into the atmosphere, carrying it elsewhere and then dropping it in sudden, intense storms.

“When you put the whole picture together, one should conclude that global warming is playing a role,” said Trenberth, head of the climate analysis section of the National Center for Atmospheric Research in Boulder, Colo. “A few degrees on top of what would already be a heat wave pushes the edge a bit more. It goes over a threshold, and things are no longer tolerable.”

On the other hand, he added: “Most of what is going on is summertime. It’s supposed to be hot. Maybe it’s bit hotter than it would be. . . . “

Randall Ceverny, a climatologist at Arizona State University, said: “If we were to see many, many more heat waves each and every year, that would be a trend associated with global warming.”

Gore and, increasingly, Clinton, have been among the more vocal political adherents of the global warming theory--reflecting the widespread agreement, but certainly not unanimity, among scientists and others who have studied data that the Earth’s climate has been growing measurably warmer, most notably in the last decade.

Both Clinton and Gore have focused their attention on the weather pattern as Congress has debated an appropriations provision that the administration says would restrict its ability to take steps intended to counter global warming and even to study the phenomenon.

“This strange pattern of weather is in keeping with the consequences that were predicted as a result of global warming,” Gore said.