Changing weather patterns have caused a sea change in the way Greenland is melting, according to a new study published Thursday. By combining data from satellites and weather stations, a team of scientists discovered that rain storms are now causing nearly a third of the rapid melting of the frozen island.
In terms of sea level rise, meltwater runoff from the upper part of the Greenland ice sheet has recently exceeded the contribution of icebergs breaking off its edges. Those runoff events are increasingly related to rain storms, even during winter, which trigger new ice melt.
"It was a surprise to see it," lead author Marilena Oltmanns of the Helmholtz Center for Ocean Research in Germany said in a statement. The researchers observed more than 300 sudden fusion episodes from 1979 to 2012, the most recent year available.
Warmer air temperatures are having a big effect on Greenland, but the warm water that falls as the rain is seemingly disastrous for the ice, breaks open through divots and crevices and melts the surrounding snow. The rain-on-snow process transforms the surface of the ice sheet from fluffy and reflective to compact and wispy, a dangerous feedback loop that is perfect for encouraging melting on sunny days.
"If it rains in the winter, that makes the ice more vulnerable in the summer," Marco Tedesco, a glaciologist at Columbia University and a co-author of the study, said in the statement. "We are beginning to realize, you have to look at all the stations."
It seems increasingly clear that the Greenland ice sheet crossed a tipping point around 2002. In the decade after that year, melting increased nearly fourfold, mainly coming from the southern part of the island which is especially prone to these rain on ice events.
Since 1990, Greenland's average temperature has risen by around 1.8 degrees C (3.2 degrees F) in summer and 3 degrees C (5.4 degrees F) in winter, much faster than the global average. In recent decades, meltwater linked to rainfall events has doubled in the summer and tripled in the winter, even though the total volume of precipitation on the ice sheet remains the same.
In a companion video filmed on the ice sheet, Tedesco compared the Greenland ice sheet to a sleeping elephant: "When we wake him up, he has the power to destroy everything that comes his way."
Greenland is losing around 270 billion tons of ice per year. That's enough to cover the entire state of Texas in more than a foot of water. That rate is accelerating, and if Greenland were to melt completely in the next few centuries, it would raise the world's oceans by about 20 feet.
With emissions reduced rapidly, scientists estimate that Greenland's melting could be limited to an additional inch or less of sea level rise, which would surely prevent a complete meltdown.
By Eric Holthaus
Article (in English)