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2012 Record Challenged as 40% of Greenland Ice Sheet Surface Melts on June 17th
18
June, 2014
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.
Links:
Hat
tip to Andy from San Diego
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