However, the meltwater of glaciers contributed almost as much to the rise in sea level in the period 2003 to 2009 as the two ice sheets: about one third. This is one of the results of an international study with the involvement of geographers from the University of Zurich.
Meltwater pounded at surface in accumulation zone, Columbia Glacier, Alaska, July 2008
Picture: W. Tad Pfeffer
How much all glaciers contribute to global sea-level rise has never been calculated before with this accuracy. An international group of researchers involving two geographers from the University of Zurich has confirmed that melting of glaciers caused about one third of the observed sea-level rise, while the ice sheets and thermal expansion of sea water account for one third each.
So far, estimates on the contribution of glaciers have differed substantially. Now 16 scientists from nine countries have compared the data from traditional measurements on the ground with satellite data from the NASA missions ICESat (Ice, Cloud and land Elevation Satellite) and GRACE (Gravity Recovery and Climate Experiment).
Combined with a glacier inventory that is available globally for the first time, the researchers were able to determine the glacier mass changes all over the world much more accurately than before. «The extrapolations of local field measurements to large regions and entire mountain ranges traditionally applied sometimes overestimated the ice loss», describes UZH geographer Frank Paul the findings from the satellite measurements. And his fellow colleague Tobias Bolch adds: «We are well aware of the weaknesses of the individual satellite methods. However, in highly glacierized regions the results obtained using the two different methods agree well. With the mix of methods that have now been tested and applied, we have come a major step closer to determining glacier mass loss with higher precision.»Earlier estimates should be corrected
The results published in «Science» have important consequences for past studies: Bolch and Paul conclude by recommending that «Earlier global estimates on the contribution of glaciers to sea-level rise should be revised again».
The UZH geographers Tobias Bolch and Frank Paul contributed important basic data for the study: digital glacier outlines for the global glacier inventory from different regions in the world for which no precise data were previously available. For example for Alaska, Baffin Island, Greenland, the Alps, high-mountain Asia including the Himalayas as well as own calculations on the mass loss in Greenland and in high-mountain Asia.Contact:
Nathalie Huber | Universität Zürich
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