Published on Wednesday, February 23, 2000 in the Los Angeles Times
Scientists: Expect Severe, Sudden Global Warming Impact
by Usha Lee McFarling
A new analysis by government scientists indicates 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. The 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 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 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 century occurred at a rate of just over 1 degree per century.
In contrast, warming since 1976 occurred at a rate of nearly 4 degrees per century. The increase in warming, Karl said, could be evidence for a ``change point'' -- a period when 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 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 over how quickly Earth is warming, what the effects of that warming may be and whether the warming is caused largely by human or natural causes. The answers are crucial, scientists said, for developing effective environmental policies.
Global warming 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 Earth's warming rate.
The hot spell continued into 1999, the fifth-warmest year on record despite the occurrence of a cooling La Nina event.
Karl cautioned that he cannot be certain that the extremely warm years of 1997, 1998 and 1999 are evidence of an increased warming trend. But a statistical analysis suggests there is only a 5 percent chance that such temperatures would not be part of a warming trend, he said.
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 Nino events known to cause warming.
``Yes, those months were unusual, but they weren't unusual due to human influences,'' he said.
Karl disagreed, saying that temperatures were far higher than could be explained by an El Nino 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 Henry Pollack, a University of Michigan geologist.
``Even if we don't understand the details of what's causing it,'' he said, ``we still have to deal with the consequences.''
Copyright 2000 Los Angeles Times