As the globe warms, keep an eye on storms.

Global warming may raise sea levels more dramatically than most climatologists expect, a new study of the ice buried within Greenland's glacier suggests. Current predictions overlook the influence of storms on Arctic snowfall, which influences ocean levels, the study's authors contend.

Global sea levels are already on the rise (SN: 12/10/94, p.388) and will continue to climb to dangerous heights as melt into the oceans, many climate forecasters agree. In their calculations, however, scientists generally assume that as the mercury climbs, more water will evaporate from the oceans and some of it will get locked up in Arctic ice, thus offsetting slightly the predicted ocean level increase.

Indeed, snowfall in Greenland will increase 4 percent with every 1[degrees] C boost in temperature, researchers from the Geneva-based Intergovernmental Panel on Climate Change (IPCC) predicted in 1990.

Wishful thinking, assert Wanda R. Kapsner of Pennsylvania State University in University Park and her colleagues in the Jan. 5 NATURE. Less snow will probably accumulate than the IPCC anticipates, so "it may be prudent to plan for somewhat larger future sea-level rises than that of the IPCC 'best-estimate' case," they report.

Kapsner and her colleagues determined the relationship between Arctic snowfalls and temperatures as far back as 18,000 years by analyzing cores from Greenland's ice cap. They dated the ice by looking at seasonal changes in the snow and estimated temperature fluctuations by examining the ice's oxygen isotopes, says coauthor Richard P. Alley, also of Penn State.

As expected, the team found that more snow fell during warmer periods. However, during times without marked changes in temperature, such as nowadays, a 1[degrees] C increase in temperature coincides with just a 1 percent hike in snowfall. Only during brief periods of dramatic warming, such as occurred when the ice age ended, did 12 to 13 percent more snow accumulate per 1[degrees] C rise.

Researchers expect global warming to cause gradual temperature changes -- and temperature-related snow accumulations -- more similar to those seen during periods of stable weather patterns than at the end of an ice age, Alley says. Therefore, the IPCC prediction for how much water will remain in the frozen Arctic, instead of in the oceans, is inflated.

Moreover, Alley argues, during the unstable times, "there's tremendously more change in snowfall than you can account for by temperature."

The culprit is storms, Kapsner and her coworkers contend. "We find that atmospheric circulation [storms], not temperature, seems to have been the primary control on snow accumulation in central Greenland over the past 18,000 years." To predict snowfall, researchers must look at the location, number, strength, and duration of storms, Alley says.

During very cold weather, such as the ice age, storms avoided Greenland, Alley says. They came back and dumped snow when the weather heated up. "Storms like to run where there's a steep temperatue gradient," so they travel along the frozen edges of an ocean or country, he explains. How global warming will alter storm patterns remains unclear, he adds.

Other studies have pointed to the importance of storms in estimating sea rise, but they have not had the extensive data collected by Kapsner's group, says David H. Bromwich of Ohio State University in Columbus.

Predicting the behavior of storms "is a much more challenging problem" than forecasting temperature, but it's equally important, Bromwich asserts.

Gases that lead to global warming will influence the frequency, intensity, and location of storms, he adds.