By Sid Perkins
From San Francisco, at a meeting of the American Geophysical Union
The duration and extent of ice melt across high-altitude portions of the Greenland ice sheet last year were the highest they’ve been in recent decades, satellite observations indicate.
By measuring microwave radiation reflected from a snow-covered patch of ice, scientists can discern if any of the snow has melted, says Marco Tedesco, an electrical engineer at NASA’s Goddard Space Flight Center in Greenbelt, Md. To gauge the severity of snowmelt across an area during a particular season, Arctic researchers developed a melting index, which is calculated by multiplying the area where snow melted by the length of time that melting occurred there.
Greenland is an island about three times the size of Texas. This year, surface temperatures across portions of the island’s ice sheet were between 4°C and 6°C above average, says Tedesco. As a consequence, snow melted in some areas for as much as 30 days longer than the average melt duration recorded from 1988 through 2006. Since 1988, the average extent of the island’s snowmelt has increased each year by 19,000 square kilometers, an area slightly smaller than the state of New Jersey.
Altogether, this year’s melting index for high-altitude portions of Greenland’s ice sheet—those above a 2,000-meter altitude—was 2.5 times the annual average from 1988 to 2006. That’s a new record, says Tedesco. For all of Greenland, 2007’s melting index was 30 percent above average, the fifth-highest melting index yet recorded. Scientists estimate that the amount of ice lost from Greenland this year alone is about twice that now present in Europe’s Alpine glaciers.
