What does the major calving event of Petermann glacier mean? We asked Professor Jason Box, a leading expert who was on board our 2009 Arctic expedition for his feedback on this issue. Here is what he has to say. (Adapted from text originally posted here).
NASA satellite images from 28 July, 2010 (left) and 5 August, 2010 (right) showing the 275 square km floating ice area detachment from Petermann Glacier. Source: Box and Decker, Byrd Polar Research Center. http://bprc.osu.edu:/MODIS
Petermann has one of the largest floating ice areas in the Northern Hemisphere. In 2009, the floating ice area was 16 km (10 miles) wide and 80 km (50 mi) long, that is, 1295 sq. km (500 square miles). Between 3-4 August, 2010, Petermann lost 275 km2 ice area as a large plate detached along a large rift.
Petermann glacier disintegration has been proceeding since year 2000, with a pause in 2009. The 2010 disintegration is 3 times larger than any previous ice area loss in Greenland, since at least year 2000. The glacier has retreated 21 km (13 mi) since year 2000. As part of this 2010 floating ice detachment, the glacier retreated 15 km (9 mi). None of the earlier satellite observations, beginning in 1962, show the glacier at such a retreated position.
Is it possible to link this event to climate change?
While it is unreasonable to pin the cracking of a glacier on Global Warming, the retreat of Petermann glacier is certainly part of a pattern of global warming.
Warming is stronger in the polar regions because melting removes reflective snow and ice cover, allowing more sunlight to be absorbed by the underlying dark ocean or land, further increasing melt rates in an amplifying ‘feedback loop’.
Satellite observations of Petermann glacier length changes. Source: Box and Decker, Byrd Polar Research Center. http://bprc.osu.edu:/MODIS
Climate Warming is amplified in the polar regions because increased melting leads to increased absorption of sunlight leading to more melting. Consequently, the polar regions, especially the Arctic, are where the most warming is observed.
Record Setting Warmth
It was the warmest Winter season and month of May on record since 1873 at Nuuk, southwest Greenland. At Upernavik, northwest Greenland, air temperatures are well above normal in 2010.
Those who may think that winter warming is irrelevant to increased melting are wrong. A warmed ice or snow volume requires less heat during summer to bring it to the melting point.
Abnormally warm air temperatures observed around Greenland this year are linked with observations of reduced sea ice concentration and warming sea surface temperatures.
What does this mean for the greater Greenland ice-sheet?
When ice is lost from the glacier front, there is less flow resistance and acceleration follows. While there is relatively little friction between Petermann glacier and the adjacent fjord walls, some acceleration is now expected. It is ominous because Petermann is among a handful of Greenland glaciers that flow through bedrock trenches extending inland to the thickest parts of the ice sheet. There is no mechanism expected to keep the retreat from moving further and further inland, hastening the demise of the ice sheet, adding to an accelerating global sea level rise.
It has yet to be shown that Petermann glacier has accelerated. GPS left on the surface in year 2009 by Alun Hubbard, if recovered this year, should document how much Petermann may have accelerated owing to the loss of the lowest 15 km of the glacier front.
Greenland glaciers have been losing ice area steadily since at least year 2000. 3/4 of the area loss has been in northern Greenland. Humboldt Glacier, immediately south of Petermann, has lost 120 square km since 2000. It too has a sub-marine trench leading into the heart of the ice sheet.
The NASA gravity-sensing satellite GRACE has detected that the Greenland ice sheet has been losing ice at an accelerating rate(1).
Greenland glaciers are discharging more ice than accumulates each year by snowfall.
This mass imbalance has spread to northwest Greenland(2).
Link with the ocean
Greenland ice sheet volume loss has increased since the mid-1990s when a warm ocean current impinged on the sub-marine parts of marine-terminating glaciers(3).
The Earth is 7/10 covered by oceans. The global oceans have uptaken an enormous amount of heat (4), far more heat than the atmosphere has during the past century-plus of human loading of the atmosphere with heat-trapping greenhouse gasses. The ultimate de-stabilization of the Greenland and Antarctic ice sheets will likely be triggered by ocean warming. Increased surface melting is a smaller part of the story.
Time Lapse Cameras to be Recovered
During a July-August 2009 field campaign, Jason Box, Byrd Polar Research Center, left behind two time lapse cameras viewing the part of Petermann Glacier that has disintegrated. Jason obviously is keen to return to the site to recover the photos to produce a movie of the ice disintegration to share with the world.
The bigger picture in Greenland
Area and effective length changes at the front of 34 of the widest Greenland marine-terminating glacier outlets are measured each year 2000-2009 in consecutive late summer satellite images (see: Box, J.E. and D.T. Decker, Greenland marine-terminating glacier area changes: 2000-2009, Annals of Glaciology, submitted). These glaciers exhibit a net area loss since 2000 exceeding 1100 km2. The greatest changes occurred in north Greenland with yearly area losses above 40 km2 observed at six glaciers. Hence, 76% of the total area change occurs north of 72ºN. The total width of marine-terminating front in our survey (416 km) retreated on average 0.75 km with a greater retreat rate north of 78ºN. Average sea ice concentration declined in all seasons and coastal areas around Greenland. The sea ice margin retreated along the southern limit of the Arctic seas ice pack. Sea surface temperatures increased in all seasons. The correspondence of sea ice concentration decline and sea surface temperature increase is consistent with broad deglaciation patterns measured by satellite.
Cumulative area change time series for the 34 widest Greenland glacier outlets to the inland ice sheet. The dotted line is the best-fit slope of the data. The Figure is from Box and Decker (submitted).
(1) Sabella Velicogna I, and J. John Wahr, 2006, Acceleration of Greenland ice mass loss in spring 2004, Nature, Vol 443|21 September 2006|doi:10.1038/nature05168 [a more recent study has been published]
(2) Khan, S. A., J. Wahr, M. Bevis, I. Velicogna and E. Kendrick. 2010. Spread of ice mass loss into northwest Greenland observed by GRACE and GPS, Geophys. Res. Lett., 37, L06501, doi:10.1029/2010GL042460.
(3) Holland, D.M., R.H. Thomas, B. de Young, M.H. Ribergaard and B. Lyberth. 2008. Acceleration of Jakobshavn Isbræ triggered by warm subsurface ocean waters, Nature Geoscience, 1, 659–664, (10.1038/ngeo316.
(4) Levitus, S., J. Antonov, and T. Boyer (2005), Warming of the world ocean, 1955–2003, Geophys. Res. Lett., 32, L02604, doi:10.1029/2004GL021592