Extreme Ice Melts: The New Normal?
Most of us are familiar with snow and ice melting as seasons change. This process even occurs in colder regions that typically have ice and snow all year round. However, last July, 98 percent of the Greenland Ice Sheet's surface melted. While losing all this snow and ice may seem normal to those of us who experience different seasons, this percentage is compared to roughly 50 percent that usually melts during an average summer.
Snow that usually stays frozen and dry in these colder areas are turning wet with melted water and research led by the Cooperative Institute for Research in Environmental Sciences now shows last summer's extreme melt could soon be the new normal.
"Greenland is warming rapidly, and such ice-sheet-wide, surface-melt events will occur more frequently over the next couple of decades," said Dan McGrath, a University of Colorado Boulder doctoral student and lead author of a paper, which reports a significant warming trend on the Greenland Ice Sheet.
McGrath and his coauthors anticipate that by 2025, ice-sheet-wide melt events will have a 50 percent chance of occurring each year. That would signal the loss of the last major dry-snow zone (regions where the snow stays almost perpetually frozen) in the Northern Hemisphere.
Researches used meteorological data and boreholes to generate a 60-year record of air temperatures at the highest and coldest station on the ice sheet.
From 1982 to 2011, near-surface temperatures increased by an average of 0.16 degrees Fahrenheit every year. "This is six times faster than the global average," McGrath said.
Warming temperatures have expanded the lower parts of the ice sheet which are losing more snow each year than they are accumulating.
"This increases the area over which the ice sheet sheds mass while shrinking the zone that gains mass," McGrath said. "That will have an obvious impact on the ice sheet's mass balance." And this imbalance will ultimately contribute to sea-level rise.
The changes could increase the amount of solar radiation the ice sheet absorbs, increasing the melt rate as well. It also could speed up the ice sheet's flow.
The summit of the Greenland Ice Sheet has experienced surface melt in the past, McGrath says. But the melt events in the past were rare, happening once every century or two - in fact, only eight times in the last 1,500 years - the exception rather than the norm. Now the norm is shifting toward a new, slushy set point.
The study was published May 20, online in Geophysical Research Letters.
Read more at the University of Colorado, Boulder.
Greenland ice sheet image via Shutterstock.