Melting over the Greenland ice sheet has loudly shattered the seasonal record on August 8 – a full four weeks before the official close of the summer melting season.
According to Professor Marco Tedesco of the City College of New York, the melting season in Greenland typically lasts from June – when the first puddles of meltwater appear – to early September, when temperatures noticeably cool.
However, cumulative melting in the first week of August 2012 exceeded the record of 2010, which was measured over a full season.
“With more yet to come in August, this year’s overall melting will fall way above the old records. That’s a goliath year – the greatest melt since satellite recording began in 1979,” explained Tedesco.
“This spells a change for the face of southern Greenland, with the ice sheet thinning at its edges and lakes on top of glaciers proliferating.”
Tedesco noted that the above-mentioned changes illustrate what most climate models predicted, albeit even more rapidly than anticipated. Indeed, to quantify the changes, he calculated the duration and extent of melting throughout the season across the whole ice sheet – using data collected by microwave satellite sensors.
Essentially, the resulting “cumulative melting index” can be seen as a measure of the “strength” of the melting season: the higher the index, the more melting has occurred.
Dr. Thomas Mote, Professor of Geography at the University of Georgia and colleague of Professor Tedesco, confirmed the cumulative melt in 2012 had already surpassed that of 2010 using a similar analysis.
It should be noted that the August 8th record differs from NASA’s recently announcement of unprecedented melting in mid-July, reported by Professor Tedesco and other researchers. Then, they found that the Greenland ice sheet had melted over 97 percent of its surface.
“That event was exceptional in the sense that it was an extremely rare event… Imagine Rio de Janeiro under a layer of snow and you get the idea.”
The extreme melting detected in mid-July generated liquid water that actually refroze after a few days.
“This changed the physical properties of the snowpack – making a slushy layer that turned into an icy crust after refreezing – but very likely it did not add to the runoff of meltwater that makes sea levels rise,” explained Tedesco.
“The cumulative melting index, on the other hand, does account for water flowing to the ocean. The same meltwater can affect ice dynamics by lubricating the base of the ice sheet and speeding its slide toward the sea.”
This year, Greenland experienced extreme melting in nearly every region – the west, northwest and northeast of the continent – but especially at high elevations. In most years, the ice and snow at high elevations in southern Greenland melt for a few days at most. However, it has already gone on for two months in 2012.
Still, Tedesco cautioned that scientists needed to be “careful” with their analyses, as we are only talking about a couple of years and the history of Greenland happened over millennia.
“But as far as we know now, the warming that we see in the Artic is responsible for triggering processes that enhance melting and for the feedback mechanisms that keep it going. Looking over the past few years, the exception has become part of the norm,” he added.