Washington, Sept 26 : A new NASA-supported study has reported that 2007 marked an overall rise in the melting trend over the entire Greenland ice sheet.

More surprising, researchers said, was the fact that melting in high-altitude areas was 150 percent more than average, adding that the amount of snow that had melted this year over Greenland could cover the surface size of the US more than twice.

Marco Tedesco, a research scientist at the Joint Center for Earth Systems Technology, cooperatively managed by NASA's Goddard Space Flight Center in Greenbelt, Md., and the University of Maryland at Baltimore County, used satellite data to compare average snow melting from 1988-2006 with what has taken place this summer.

He found that in high altitude areas over 1.2 miles above sea level, the melting index – an indicator of where melting is occurring and for how long – was significantly higher than average.

Melting over those areas occurred 25-30 days longer this year than the observed average in the previous 19 years.

“When snow melts at those high altitudes and then refreezes, it can absorb up to four times more energy than fresh, unthawed snow,” said Tedesco.

“This can affect Earth's energy budget by changing how much radiation from the Sun is absorbed by the Earth versus that reflected back into the atmosphere. Refrozen snow can also alter the snow density, thickness and snow-water content,” he said.

Scientists determine the melting index by multiplying how long melting took place by the area where the increased melting took place.

According to Tedesco, melting in April and May of this year in high-altitude areas was very low, but in June melting jumped unexpectedly and led to the record- melting index for the year.

“This record melting index in those areas came as a bit of a surprise, showing us, once again, the extreme variability and complexity of these processes,” said Tedesco.

The study also confirmed that the melting index this year in lower altitude areas of Greenland, though not record breaking, was higher than average by 30 percent, placing 2007 in fifth place for the highest melting index after 2005, 2002, 1998 and 2004, in that order.

Tedesco's findings were published Sept. 25 in the American Geophysical Union's Eos newspaper. (With inputs from ANI)