Edition: U.S. / Global

IDEAS & TRENDS;Blame Global Warming for the Blizzard

Published: January 14, 1996

IT seems a paradox at first glance: How could a record snowstorm have covered much of the northeastern United States last week when the climate of the earth is warming?

Just four days after scientists announced on Jan. 3 that the average surface temperature of the globe had crept to a recorded high of nearly 60 degrees in 1995, the Blizzard of 1996 dropped more than 20 inches of snow on Central Park, the third deepest snowfall ever measured there. More than two feet fell on other parts of the Northeast corridor.

But not only are blizzards and global warming compatible, some experts cite evidence suggesting that climatic changes associated with global warming are actually creating more severe snowstorms.

The apparent planetary warming is unlikely to nullify the seasons, including winter, although some climatologists say severe cold spells should eventually become less frequent if the warming continues as predicted.

Frigid masses of Arctic air still rule the polar winter, and a southward bulge of this polar chill was a crucial element in producing the blizzard. Another such bulge has been responsible for the bitter weather frustrating American troops in Bosnia. Seasonal movements of air like these easily overwhelm the relatively small amount of global warming observed so far.

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Moreover, other parts of the globe have been unusually warm despite the cold start to winter here and in Central Europe.

While the blizzard paralyzed New York, Southern California enjoyed record warmth. The summertime temperature in Argentina at a latitude roughly comparable to that of Washington, D.C., soared to 110 degrees a few days ago.

And even where it has been cold, global warming may be contributing to heavier snowfalls and greater extremes of precipitation generally.

A warming atmosphere causes more evaporation of water from the ocean, which means more rain, snow or sleet. The conversion of more water from vapor to precipitation also releases more energy into the atmosphere, making storms more powerful. In cases where atmospheric circulation conspires to keep rain away from a given area, as happens from time to time, a warming climate is expected to produce hotter heat waves and more severe droughts.

Extremes of this kind are becoming more frequent, say researchers at the National Climatic Data Center in Asheville, N.C.

Last year, the researchers analyzed temperature and precipitation records for the 20th century and found that from 1980 through 1994, the incidence of extreme one-day precipitation, over-all precipitation, above-normal temperatures and drought had risen in many areas of the country.

By comparing this pattern with the pattern of climate change that computer simulations indicate should result from an increase in heat-trapping "greenhouse" gases like carbon dioxide, the analysts concluded that there is a 90 to 95 percent chance that the increase in extremes was caused by the increase in greenhouse gases.

An authoritative group of scientists advising the United Nations recently concluded for the first time that the greenhouse gases -- produced by the burning of coal, petroleum and wood -- are probably responsible for at least part of the observed warming.

The average surface temperature of the earth has risen by about 1 degree Fahrenheit in the last century. The scientists forecast a rise of another 3.6 degrees over the next century if emissions of the gases are not reduced, the most rapid global temperature change in the last 10,000 years, with further warming after 2100.

That may not sound like a lot of warming, but the average global temperature is only 5 to 9 degrees higher now, depending on varying calculations, than it was in the depths of the last ice age.

If the scientists are right, extreme weather will be a hallmark of the changing climate, and in fact may be the most common way in which people experience global warming.

One particularly revealing index of extremity is the amount of precipitation in a 24-hour period. Extreme rainstorms, snowstorms, ice and sleet storms, have become more frequent in the United States, and several locations reported record 24-hour snowfalls last week.

The Blizzard of 1996 does indeed qualify as one type of extreme weather to be expected in a warmer climate.

"It's another statistic that adds to the record" of extreme precipitation, said Thomas R. Karl, the leader of the Asheville research team that is studying the phenomenon. "It's rather interesting. We seem to be getting these storms of the century every couple of years." Mr. Karl has not been known as a doom-sayer on the question of global warming.

As Northeasterners showed last week, people can adapt to extreme weather, but at costs both monetary and human.

The blizzard may have cost the New York region a billion dollars and it caused many deaths. Floods resulting from extreme rains, like the historic ones in the Mississippi basin in 1993, take a toll both in dollars and disaster. Extreme heat waves like last summer's in Chicago, which Mr. Karl says may have been worsened by global warming, impose extreme and often lethal hardships on the old and weak. Developing countries, many of which have fewer resources to cope with a changing climate, are generally regarded as most vulnerable.

For all the tantalizing signs and signals, it remains uncertain as to whether human activity is changing the climate a little or a lot, and if a lot, how drastic the change will ultimately be.

Long-range climate forecasting is no more precise than short-range weather forecasting, both based on an imperfect understanding of the turbulent atmosphere and on equally imperfect analytical tools like computer simulations of the atmosphere's workings.

Sometimes, the task of predicting the weather a season ahead is made easier.

For instance, forecasters know that the quasi-periodic appearance of El Nino, the vast pool of warm water in the equatorial Pacific, increases the probability of certain atmospheric events. They can predict that when El Nino appears, the northern jet stream, the high-altitude river of air that girdles the northern hemisphere, will shift to a course that blocks any invasions of polar air in the northeastern United States.

That was the case a year ago. Forecasters at the Climate Analysis Center of the National Weather Service at Camp Springs, Md., predicted a mild winter for the Northeast last year. They were right; on Jan. 13, 1995, for instance, the temperature reached 61 degrees in Central Park.

This year, El Nino has disappeared. The Weather Service nonetheless predicted a warm winter again based on previous weather patterns, but that forecast has turned out to be wrong so far. The winter is young enough that the forecast could still be right in the end. If not, it will be testimony to the hazards of trying to gauge the behavior of the atmosphere far in advance.

"It comes with the territory, and we accept that," said Ed O'Lenic, who heads the Climate Analysis Center's forecast operation.