Ice volume of Switzerland's glaciers calculated

Swiss glaciers have lost a lot of ice in recent years due to increased melting. As temperatures climb, so do the fears that the glaciers could one day disappear altogether. Until now it could only be estimated approximately how big the ice volume in the Swiss Alps actually is and how it has changed in recent years. A team of scientists headed by Martin Funk, ETH-Professor at the Laboratory of Hydraulics, Hydrology and Glaciology (VAW) at ETH Zurich, however, has now developed a novel procedure for determining the ice volume of a glacier. Their results are presented in the current issue of Global and Planetary Change.

The researchers developed the new method according to the law of mass conservation, which states that the surface mass balance has to be balanced by the ice flow and the change in ice thickness. This allows to infer on the ice thickness distribution of a glacier from the surface topography by estimating the mass balance distribution. 'The calculation of the current ice volume is the most important indicator in predicting future glacier changes,' explains Martin Funk.

The scientists applied the procedure to the 59 Swiss glaciers larger than three square kilometres. For the remaining 1,400 glaciers, the ice volume was estimated by using an empirical area-volume approach derived from the new generated data set. The total glacier ice volume in 1999 was estimated to 74 km3, with an accuracy of 9 km3. This means the total volume of all glaciers of Switzerland is smaller than that of the Lake Geneva, which has a water volume of 89 km3. With a glaciated land area of 1,063 km2, the Swiss glaciers have an average ice thickness of 70 metres.

The scientists also discovered that the 59 larger glaciers account for almost 88% of the ice volume, whereas about 24% is stored in the Aletsch region alone (the Oberaletschgletscher, Mittelaletschgletscher and Grosser Aletschgletscher). The area of the Great Aletsch Glacier is approximately the same as the total area of all the Swiss glaciers smaller than one square kilometre. However, they have an overall ice volume that is twenty times smaller than that of the Grosser Aletschgletscher. 'This just goes to show that the large glaciers carry the most weight in determining a region's ice volume,' explains Funk.

The ETH Zurich study also revealed a change in the ice volume since 1999. Over the last decade - the warmest for 150 years - Switzerland's glaciers have lost 9 km3 of ice (-12%), including 2.6 km3 (-3.5%) in the record-breaking sum-mer of 2003 alone. These figures are all the more alarming as the climate con-tinues to warm up and the temperatures in the Swiss Alps are expected to in-crease by 1.8 degrees in the winter and 2.7 degrees in the summer by 2050.