MODIS Studies of Greenland

Between 3 and 5 August, 2010, 275 square kilometers (106.2 square miles) of the front of the floating Petermann Glacier, far northwest Greenland, broke away. This is the largest single area loss observed for Greenland. Petermann is one of a few remaining floating glaciers in the Northern Hemisphere and among the largest.

click here for a higher resolution version of the above graphic

This area is more than three times that of Manhattan Is, New York.

The glacier effectively retreated 15 km (9 miles).

We have been measuring Petermann glacier area changes in a survey spanning 2000-2009. Consulting other publications and imagery, we conclude that this is a retreat to a new minimum in available satellite observations since 1962. Eric Rignot observed that “Petermann was not that far back when first visited by the Lauge Koch expedition in the 1920s”.

Petermann glacier disintegration has been progressing since year 2000, with a pause in 2009. Petermann has retreated 21 km (13 mi) since year 2000. The 2010 disintegration is 3 times larger than any previous ice area loss in Greenland, or the Northern Hemisphere for that matter, since at least year 2000.

click here for a higher resolution version of the above graphic

Is it possible to link this event to climate change?

While it is unreasonable to pin an individual cracking event of a glacier on Global Warming, even if enormous, the retreat of Petermann glacier is most certainly part of a pattern of global warming.

It is safe to say that glaciers retreat in a warming climate.

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 a ‘feedback loop’.

Record Setting Warmth
2009/2010 winter and the month of May were the warmest 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 need recognize that 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 (reference 1). Greenland glaciers are discharging more ice than accumulates each year by snowfall. This mass imbalance has spread to northwest Greenland (reference 2).

The important 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 (reference 3).

The Earth is 7/10 covered by oceans. The global oceans have uptaken an enormous amount of heat (reference 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

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. Insufficient resources are currently in hand to finance the helicopter charter to return to Petermann glacier to gather the images. Partnership is sought to bridge the funding gap. Contact: Jason Box

Two Extreme Ice Survey (EIS) time lapse cameras have been photographing every half-hour of daylight at Petermann Glacier for the last 13 months. The photographs will be recovered in early September, enabling the EIS team to assemble time-lapse videos. Jason Box will use these data to measure speed changes and analyze the dynamics and processes of the Petermann breakup.

This blog entry was composed by Jason Box. David Decker and Russ Benson at Byrd Polar Research Center assisted with satellite image area analysis and graphics, respectively.

References

1. 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