LOS ANGELES TIMES        Wednesday, February 23, 2000

Climate Is Warming at Steep Rate, Study Says
Weather: Effects could be severe, federal researchers warn. Scientists still debate if man or nature is to blame.

By USHA LEE MCFARLING, Times Science Writer

     A new analysis by government scientists indicates the Earth's climate is warming at an unprecedented rate, suggesting that the future impact of global warming may be more severe and sudden than predicted.
     Such a steep warming rate was not expected to occur until well into the 21st century, said Tom Karl, the National Oceanic and Atmospheric Administration climatologist who led the study. Such a trend probably would mean a continuation of the recent three-year string of steamy summers and mild winters seen by much of the nation, and eventually perhaps increased flooding of low-lying areas. "The next few years are going to be very interesting," Karl said. "It could be the beginning of a new increase in temperatures."
     Historical and geological records show that the Earth warms and cools in fits and starts, not at a constant rate. During the 1900s, most warming occurred between 1910 and 1940 and then after 1970. On average, though, warming throughout the 1900s occurred at a rate of just over 1 degree per century.
     In contrast, warming since 1976 occurred at a rate of nearly four degrees per century. The increase in warming, Karl said, could be evidence of a "change point"--a period when the Earth's climate begins warming at a faster rate.
     The analysis, which will be published in the March 1 issue of the journal Geophysical Research Letters, already is generating much interest, and some disagreement, among climatologists.
     The current debate is not over whether the climate is warming. Most scientists now agree that the Earth has warmed significantly since the 1880s when temperatures were first routinely recorded.
     Earlier this year, a blue-ribbon panel of climate experts commissioned by the National Academy of Sciences quashed most lingering doubts by calling global warming over the past 100 years "undoubtedly real."
     Questions now center on how quickly the Earth is warming, what the effects of that warming may be and, most heatedly, whether the warming is caused largely by human or natural causes. The answers are crucial, scientists said, to development of effective environmental policies.
     The global warming issue began receiving renewed attention in 1997, which was the hottest year on record. Until 1998.
     "In 1998, each month we were breaking the previous year's all-time global high temperature record," Karl said. The intense two-year string of warm months prompted Karl and colleagues Richard Knight and Bruce Baker to analyze the Earth's warming rate.
     The hot spell continued into 1999, which was the fifth warmest year on record despite the occurrence of a cooling La Nina event.
     Karl cautioned that he could not be certain that the extremely warm years of 1997, 1998 and 1999 were evidence of an increased warming trend. But a statistical analysis suggests that there is a chance of only 5%--or 1 in 20--that such temperatures are not part of a warming trend, he said.
     A number of other climatologists agree that the extreme warming of the late '90s is an ominous sign.
     "That rate is not only unprecedented in the instrumental records [since 1880] but unprecedented in the last 1,000 years at least," said Jonathan T. Overpeck, director of the University of Arizona's Institute for the Study of Planet Earth and an expert in paleoclimatic records. "There is no known precedent of natural forces that could have given rise to the temperatures of the last decade."
     Moreover, an analysis published last week in the journal Nature by Henry N. Pollack, a University of Michigan geologist, showed that the 20th century was the warmest of the last five centuries.
     "Certainly the rate of warming over the last two decades has been remarkable," he said. "The question is whether it's a short-term trend or a longer trend."
     The issue is complex because climate is affected by a mix of natural events, such as volcanic blasts, solar energy fluctuations and changes in ocean circulation, and also by human activity, such as the emission of greenhouse gases into the atmosphere. The Earth also has a number of large-scale natural climate cycles, like those that caused glaciers to form and retreat long before humans evolved.
     Tom Wigley, a senior scientist at the National Center for Atmospheric Research in Boulder, Colo., said he found the new analysis interesting but questioned whether recent warm years should be attributed to a large shift in human-induced global warming. The period between May 1997 and August 1998, he noted, included El Niño events known to cause warming.
     "Yes, those months were unusual, but they weren't unusual due to human influences," he said.
     But Karl disagreed, saying that temperatures were far higher than could be explained by an El Niño event. And 1999, he said, was the fifth hottest year on record, despite being a cool La Nina year.
     Effects of global warming--from a longer growing season in Alaska to thinning of Arctic sea ice and the flooding of some low-lying islands--have already occurred, said Michigan's Pollack.
     "Even if we don't understand the details of what's causing it," he said, "we still have to deal with the consequences."