MORE FUEL FOR THE GLOBAL WARMING CAMP

Edited by Douglas Harbrecht

Are humans warming the globe? This may be the biggest environmental question of our time, and the stakes are huge. If carbon dioxide emitted by the burning of fossil fuels, along with the release of other so-called greenhouse gases, does raise global temperatures significantly, the result could be disastrous. On the other hand, if the temperature change will be small or nonexistent, then measures to cut emissions of these gases will be a colossal waste of money.

That's why every new scientific study on the topic generates a huge amount of attention. And now, researchers are publishing one more important study, which adds fuel to the notion that humans are, in fact, warming up the Earth.

In the study, reported in the Apr. 23 issue of Nature, scientists at the University of Massachusetts and the University of Arizona reconstructed the global climate for the past 600 years. Since no one was bothering to take the necessary temperature readings for much of that time, the researchers used some clever sleuthing to peer back in time. Various methods included analyzing ice from holes drilled into glaciers, counting and measuring tree rings, and poring over records of glacier size.

The result of pulling together all this data is striking. The temperature record shows, for instance, that there was a strong El Nino in 1791 -- an event that has been suggested by historical documents. It also showed a dramatic cooling over much of the globe in 1816, caused by the massive eruption of the Indonesnian volcano, Tambora. And it shows that the 17th and 19th centuries were the coolest of the study period.

But, most important, the temperature record shows that the three warmest years since 1400 were all in the 1990s - - 1990, 1995, and 1997. That doesn't necessarily mean human activity is warming the globe. Indeed, global warming skeptics argue that this is simply natural variation. But to many scientists, the evidence is mounting that humans are responsible. "The anomalous warmth of several recent years appears likely to be related to human influences on climate," says UMass geoscientist Michael E. Mann. Adds Herman Zimmerman, head of atmospheric science research at the National Science Foundation: "The study adds solid information to the growing base of data which points to the warming of our planet by human-related activities."

It's not the last word, by any means. But it's bound to turn up the heat on the skeptics.

By John Carey in Washington