Paris, 15 January 2010
Mountain glaciers cover between 500 000 and 600 000 km2 of
the Earth's surface (around the size of
Of all the ice-covered regions of the planet, ice loss has been the
How did the team from the Geophysical Institute of the
Why did they overestimate ice loss from these glaciers by 50%? The impact of rock debris that covers certain glacier tongues (4) and protects them from solar radiation (and thus from melting) was not taken into account in the previous work. Moreover, their sampling was limited to longitudinal profiles along the center of a few glaciers, which geometrically led to overestimation of ice loss.
This new study confirms that the thinning of Alaskan glaciers is very uneven, and shows that it is difficult to sample such complex spatial variability on the basis of a few field measurements or altimetry profiles. Thanks to their regional coverage, satellite data make it possible to improve observations of glacial response to climate change and to specify the contribution of glaciers to sea-level rise.
Ice loss from Alaskan glaciers since1962 is evidently smaller than
previously thought. However, thinning (sometimes over 10 m/year, as in the
SPIRIT project image gallery:
© M. J. Hambrey (Aberystwyth University) Field campaign on the Saint Elias glaciers (Alaska and Yukon Territory).
© M. J. Hambrey (Aberystwyth University)
Field campaign on the Saint Elias glaciers (Alaska and Yukon Territory).
(1) from Northern Arizona University (US) and two universities in Canada (University of British Columbia and University of Northern British Columbia).
(2) During the 4th International Polar Year (2007-2009), the glaciologists had free access to SPOT 5-HRS data thanks to the SPIRIT project (SPOT 5 stereoscopic survey of Polar Ice: Reference Images and Topographies). The high-resolution images from this satellite can be used to reconstruct precisely the topography of polar ice and thus study its past and future evolution in response to climate fluctuations. LEGOS is the scientific coordinator for this project, which was carried out with CNES, Spot Image and IGN Espace.
(3) Arendt et al, Rapid wastage of Alaska glaciers and their contribution to rising sea level. Science 297, 382-386 (2002)
(4) The lower parts of a valley glacier.
Berthier E., Schiefer E., Clarke G.K.C., Menounos B. & Remy, F. Contribution of Alaskan glaciers to sea level rise derived from satellite imagery. Nature Geoscience, 3(2), 92-95, doi: 10.1038/ngeo737, 2010
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