NASA scientists reading signals from a satellite in orbit, and flying aboard a low-flying plane over Greenland, are finding fresh evidence of melting snows and thinning glaciers in vast areas of the massive island.Their observations confirm the climate's warming trend in the far northern reaches of the world, they say, where changes in the circulation of waters feeding into the Arctic Ocean are altering crucial patterns of ocean currents there with effects that are increasingly uncertain.
The pace of glaciers sliding into the sea along Greenland's southwestern coast "is speeding like gangbusters this year," said William Krabill, leader of a NASA team that has just ended a three-week airborne mission probing glacier dynamics with lasers and radar.
In order to avert distortion by dense clouds, the team flew crisscross patterns over the ice at altitudes no higher than 1,500 feet, Krabill said Friday in a telephone interview from his base at NASA's Wallops Island Flight Facility in Virginia.
In similar flights seven years ago, he recalled, data gathered by instruments aboard the plane showed that glaciers were moving into the ocean at a rate of only about 6 feet a year. But seven flights this spring, covering 16,000 miles of Greenland's surface and coastal glaciers, revealed that ice along the southern coast is speeding to the sea at more than 75 feet a year, Krabill said.
The island's huge ice sheet is 2 miles thick at the center, and Krabill's team has been monitoring the inland surface and the glaciers flowing into the sea every year for the past 15 years. It's clear, he said, that the entire island has been losing significant amounts of ice year by year.
And while the glaciers are on the move, Greenland's snows have been melting over large areas of the ice sheet, according to Marco Tedesco, a research scientist at NASA's Goddard Space Flight Center who has been working on a joint climate study project with the University of Maryland.
Data from a Defense Department meteorology satellite show that last spring the snow on Greenland melted over an area of more than 375,000 square miles -- nearly 2 1/2 times the surface area of California, Tedesco said Friday in a telephone interview. That was far more than the island's average summertime snowmelt area of 350,000 square miles, he said.
Eighteen years of the satellite observations have shown that while the fluctuating trend of melting ice continues, Tedesco said, last summer didn't set the all-time record for snowmelt area on Greenland's surface. For example, five summers ago the melting snow covered more than 540,000 square miles -- nearly 3 1/2 times California's area, he said.
The satellite data also showed that last summer the island experienced more days of melting snow and at higher altitudes than the average of all the past years -- particularly in the southern part of the island, he said.
Melting snow is more significant than just another indicator of global warming, both Tedesco and Krabill said, for in many areas near the coast the water can drain through surface cracks and vertical passages inside the glaciers and reach bedrock where it lubricates the ice sheet and speeds the flow of the glaciers to the ocean.
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