To study the history and future of heat, look at ice. That's the theory behind the latest evidence pointing toward the likelihood of global climate change. And what these studies are showing is that massive ice packs near the North and South Poles are diminishing in size.
Using precise aerial mapping, NASA scientists have found that Greenland's ice cap is "rapidly thinning" - at a rate of more than three feet a year in some places.
"A conservative estimate, based on our data, indicates a net loss of approximately 51 cubic kilometers [11 cubic miles] of ice per year from the entire ice sheet," says William Krabill, NASA project scientist and lead author of a report published in the current issue of the journal Science. "When we go back after five years and see 10 meters of glacier gone, there is something happening."
Some of this loss is in the form of fresh water as the ice melts into the North Atlantic. The melting also hastens the breaking off of icebergs - a process called "calving." The result is a small but perceptible addition to a general rise in the sea level observed over the past century.
"This amount of sea-level rise does not threaten coastal regions," says Mr. Krabill, "but these results provide evidence that the margins of the ice sheet are in a process of change." This latest data coincides with other information gathered by submarines, whose sonar equipment shows that the thickness of the Arctic sea ice has declined in recent years.
At 840,000 square miles, Greenland is the world's largest island. Eighty-five percent of it is covered with ice that is up to two miles thick. Over a seven-year period, NASA used airborne laser altimeters and precision global positioning satellite receivers to detect changes in elevation there. Next year, NASA will launch a special satellite to survey major ice sheets around the world.
Drilling deep core samples of ice in Antarctica gives clues to the possibility of global warming as well. One test showed that the amount of greenhouse gases trapped in the ice some 150 years ago (principally carbon dioxide) was approximately 25 percent less than in ice samples taken since the beginning of the industrial revolution. It may or may not be related to climate change, but earlier this year two of the largest icebergs on record broke away from Antarctica.
Whether or not global warming exists remains a contentious issue - particularly the degree to which this is part of a natural cycle or caused by industrial pollution and other things linked to development in the modern era.
"The earth's atmosphere is not warming and fears about human-induced storms, sea-level rise, and other disasters are misplaced," Fred Singer, professor emeritus of environmental sciences at the University of Virginia, told a Senate hearing last week.
A long-term trend?
Dr. Singer is particularly critical of the computer models used to predict the future of climate based upon what some feel is sketchy historical data. He and other skeptics note that data taken from satellites and balloons show no warming of the atmosphere, and they attribute surface temperature increases to such short-term weather phenomena as El Nio.
Still, most climatologists agree that average temperatures have been rising in recent years. For example, this spring was the warmest on record. The 1990s were the hottest decade ever recorded, and each year of that decade is among the hottest 15 years since temperatures first were recorded in 1880.
Earlier this year, a group of scientists organized by the National Research Council, which is affiliated with the National Academy of Sciences, reported that the warming of the earth's surface is "undoubtedly real," with temperatures in the past two decades rising "at a rate substantially greater than average for the past 100 years."
Whether or not this is due to global warming caused by human development, a growing number of companies whose activities are tied to greenhouse gases thought to cause climate change are taking voluntary steps to reduce such emissions.
The Global Climate Coalition, an organization of business trade associations in Washington, reports that "electric utilities have reduced greenhouse-gas emissions by 174 million tons through efficiency and process improvements." The steel and concrete industries have reduced energy consumption by 45 percent and 30 percent respectively, according to the coalition, which opposes international agreements directed at global warming while advocating voluntary measures.
Meanwhile, scientists will continue to keep an eye on the polar ice caps as an indicator of climate change.
(c) Copyright 2000. The Christian Science Publishing Society