Researchers studying an ancient ice core from Greenland said Wednesday atmospheric changes - more than the commonly believed factor of global warming - may produce more snow in cold regions.
Richard Alley of the Pennsylvania State University and colleagues found accumulation rates in the Greenland ice cap over the past 18,000 years indicate atmospheric circulation has been at least as influential as rising temperatures in snow levels."There are two theories about what happens when the Earth warms up," said Wanda Kapsner, one of the researchers. "One holds that the ice sheets will melt and the sea level will rise, flooding large coastal areas."
But many meteorologists and glaciologists disagree with this scenario, theorizing instead that a thermodynamic effect takes over, one that will make up for the ice that melts off the edge of ice sheets and mitigate a rise in sea level.
"Many believe that increased temperatures worldwide will allow the atmosphere to hold a higher percentage of moisture," said Alley, Penn State associate professor of geosciences, "that when that moist air rises over the ice sheets, more snow will fall and offset the melting."
The scientists analyzed the ice core's temperature and accumulation records to determine which of these theories is correct.
Snow accumulation may not make up for ice melting after all, they said in the British journal Nature.
"Snow accumulation in central Greenland is controlled more by atmospheric dynamics than temperature," said researcher C.A. Shuman of the National Aeronautics and Space Administration Goddard Space Flight Center.
During climate intervals when temperature rises or falls gradually, the sensitivity of snowfall to the changes was low, the researchers found, with a rise in temperature not necessarily causing higher snow accumulation rates.
During rapid temperature changes, however, the rate was surprisingly high.
"The rate of snow accumulation during rapid climate warming is greater than we would expect if only temperature were responsible," said researcher S. Anan-da-krish-nan of Penn State. "Something additional is forcing the snowfall."
That additional element, said Kapsner, is atmospheric dynamics - how big the storms are and the paths they travel.
While increased temperature allows the air to hold more moisture, it is only when snow falls on an ice sheet that the ice lost to melting would be offset. Moisture-laden air over the ocean does not add to the snow accumulation, scientists said.
"Our research indicates previous estimates of a 4 percent increase in snow accumulation for every degree increase in temperature on the Greenland ice sheet are too high," said P.M. Grootes of the University of Washington.