Yesterday, 40% of the surface of Greenland melted.
It was still mid-June, yet a month before melt values typically peak. But a persistent high pressure system over Greenland, a rapidly melting Baffin Bay and warm winds riding up the west coast were enough to spur a surface melting event that shoved melt coverage firmly above the two standard deviation threshold and into record range.
(Greenland Melt Extent as of June 17, 2014. Image source: NSIDC.)
Temperatures along the west coast of Greenland and on through the southern ice-covered tip ranged between 30 and 55 degrees Fahrenheit, while 30-43 degree readings surrounded much of the periphery. Warm winds and rain to mixed precipitation accompanied a moisture-laden storm emerging from Baffin Bay and passing over the western ice sheet to add further and extreme early season melt pressure.
The warm storm and rains compounded already rapid melt pond formation along Greenland’s southwestern coasts. Large blue ponds varying between .5 to 3 kilometers in width had already formed over southern and western sections of the ice sheet by June 16, before they were covered in clouds and squally wet weather on June 17th. By today, the clouds cleared as the passing storm moved on to reveal melt ponds further swelled by a combination of warmth and wet weather:
(Large expanse of melt ponds near the outlet to the Jacobshavn Glacier on June 18, 2014. The smallest blue dots represent glacial melt ponds of about 300 meters in width. The largest exceed 3 kilometers at the widest point. Image source: LANCE-MODIS.)
Melt ponds add heat amplification to the glacier surface by reducing albedo even as they provide melt drainage to the glacial base. Floods of water from melt ponds add to glacier speed and buoyancy by reducing friction at a moving glacier’s base and by flooding geographic low points beneath the glacier. Melt ponds also reduce overall ice sheet integrity by permeating the ice with holes and fractures.
The Jacobshavn Glacier in the satellite shot above is Greenland’s fastest. It is now involved in a very rapid rush toward the ocean at a rate of 46 meters per day. A rush that has been facilitated in recent years by a major proliferation of melt ponds during summer time.
During extreme events, melt ponds can combine and over-top or break ice dams in dangerous glacial outburst floods. It is worth noting that Greenland melt pond proliferation has not yet reached a threshold for high risk of such events. But the now decade-long proliferation of melt ponds over the ice sheet surface during summer time remains a troubling occurrence.
40% melt coverage in mid June is an extraordinarily high number. Last year, melt coverage peaked at 47% in late July with June values approaching the high 20s in late June. July of 2012 saw a 97% melt coverage — an event last seen about 120 years ago and one that is, unfortunately, likely to be repeated soon under current human heat forcing. It is worth noting, however, that the record year of 2012 saw Greenland melt coverages periodically exceeding 40% from mid-to-late June.
(Greenland melt coverage on June 17 of 2014. Image source: NSIDC.)
Early melt and proliferation of melt ponds along with persistent high pressure systems over Greenland tend to have a compounding effect that amplifies over-all melt coverage. Low mists and clouds tend to form during such conditions, trapping heat near the ice surface even as albedo over the ice sheet falls due to wide-scale melt pond formation.
Though yesterday’s melt coverage is an early challenge to melt levels seen during 2012, current conditions would have to both persist and intensify for the broad extent of melt seen during late June and through July of 2012 to show a rough repeat. That said, a 40% melt coverage on this date is a record-challenging level that bears watching.
Hat tip to Andy from San Diego