HURRICANES, FIRES ASIDE, WORLD'S WEATHER NOT BAD : GLOBAL CLIMATE STAYING RELATIVELY STABLE, SCIENTISTS SAY.

Byline: Anthony R. Wood Knight-Ridder Newspapers

Hurricane after hurricane has marched across the Atlantic Basin to menace the East Coast. In the parched West, raging fires have turned millions of acres to charred sticks.

This follows an extraordinary period of eventful weather across the nation that saw record snows in the Northeast and record drought in the High Plains.

All this may suggest an atmosphere out of control.

They might get an argument in some places, but climatologists assure us that the sky is not falling. Actually, they say, we have been enjoying a relatively tranquil period in the world's climate history.

They assure it has been worse than this, and not all that long ago. ``The 1930s are particularly grim on the national level,'' said Jonathan T. Overpeck, head of the paleoclimatology program at the government's Geophysical Data Center, in Colorado.

And as bad as the Dust Bowl era was, according to some recent research it was a picnic in the park compared with earlier epochs. That research suggests that for all the attention focused on fears of human-enhanced warming, albeit merited, the climate has enormous potential to change without man's help. A lifetime, it seems, is not nearly long enough to witness all the weather there is.

Researchers now know that the term ``normal'' is a misnomer and that the climate has changed in scales of millions of years, centuries and decades. No one is sure how or why. ``It's not a very precise science because there's no predictors that tell you what you should be looking at,'' said Robert Quayle of the government's National Climate Data Center, in North Carolina.

Data Center researchers say they have seen some indications of more extreme conditions over the last 20 years, compared with the rest of the 20th century. They suspect that those conditions, that include more episodes of heavy rainfall, are related to global warming.

The world's temperature has increased about 1 degree over the last 100 years, and many of the world's scientists, Overpeck among them, believe human activity has contributed to that warming.

That is uncertain, however. Overpeck said the warming could be natural, the planet's way of rebounding from the so-called Little Ice Age, an irregular period of cooling that lasted from about 1500 to 1850.

With or without human intervention, however, evidence gathered from tree rings, ice cores and other sources indicates that the climate is capable of abrupt and perilous changes.

In the early 19th century, not long before the U.S. Great Plains were heavily settled, they were covered with sand dunes, according to Overpeck's research. That level of duning would have required more than the roughly five years of drought in the 1930s.

``Whatever happened before that gave rise to these dune fields had to be worse than the Dust Bowl,'' Overpeck reasoned. He also discovered evidence of far more severe droughts, centered in the Sierra Nevada region.

``If you go back further in time, you see droughts that lasted not five years, not 10 years, but a hundred years,'' he said. That 100-year drought occurred about 1,000 years ago.

Going back even further, Richard Alley, a researcher at Pennsylvania State University, has found abrupt changes that today would be unimaginable.

``Up to 8,000 years ago, the world was reasonably crazy,'' he said. ``Since then it's been rather boring.

``When we look at the record, from 100,000 to 8,000 years, there are tremendous jumps,'' he said. He has found swings of 8 to 10 degrees Celsius in periods of 20 years or less, perhaps as little as one to three years.

Such swings would have dramatic consequences for the world's climate. The Intergovernmental Panel on Climate Change predicts that greenhouse gases would cause temperatures to rise 0.5 to 2 degrees Celsius by 2050, and that would be disruptive enough.

Alley drew his conclusions by studying ice-core samples from Greenland, one of several methods used by paleoclimatologists to reconstruct past climates. Overpeck has studied tree rings and sedimentary deposits.

An ice core is a treasury of climate information, according to Alley. ``It's a little bottling plant for old air,'' he said.

From ice cores, researchers can divine methane content, temperature and precipitation, even smoke from forest fires. They can read the salt content of water, and from that determine how much ice covered the Earth at any given time.

Alley and Wallace Broecker, a researcher with the Lamont-Doherty Earth Observatory in Palisades, N.Y., hold that the abrupt changes in temperature probably were related to drastic changes in oceanic circulation. That circulation is immensely complex, but it works something like a conveyor belt. Warm surface waters from the south travel into the far reaches of the North Atlantic, where it becomes saltier and cooler and thus heavier. It sinks to the bottom of the sea and returns southward.