Thursday, January 13, 2011

Goodbye Mountain Glaciers, hello sea level rise

Fox Glacier
Photo: Fox Glacier in New Zealand (2007) by Andrew Turner

New research from Canada says that most mountain glaciers are on the retreat. Many glaciers in Europe, New Zealand, Africa and the US Rocky Mountains will lose up to 75 per cent of their mass by the end of the century. The study reveals that the melt from mountain glaciers will contribute up to 12 centimetres of sea level rise by 2100.


“There is a lot of focus on the large ice sheets but very few global scale studies quantifying how much melt to expect from these smaller glaciers that make up about 40 percent of the entire sea-level rise that we observe right now,” says Valentina Radic, a postdoctoral researcher with the Department of Earth and Ocean Sciences and lead author of the study.

The study excluded from the results increases in sea levels caused by the melting of the Greenland and Antarctic ice sheets, and the thermal expansion of water.

Modelling of future glacier melt was based on temperature and precipitation projections from 10 global climate models used by the Intergovernmental Panel on Climate Change.

The paper was published in Nature Geo-Science. According to the abstract:

We conduct the simulations directly on the more than 120,000 glaciers now available in the World Glacier Inventory, and upscale the changes to 19 regions that contain all mountain glaciers and ice caps in the world (excluding the Greenland and Antarctic ice sheets). According to our multi-model mean, sea-level rise from glacier wastage by 2100 will amount to 0.124±0.037 m, with the largest contribution from glaciers in Arctic Canada, Alaska and Antarctica. Total glacier volume will be reduced by 21±6%, but some regions are projected to lose up to 75% of their present ice volume. Ice losses on such a scale may have substantial impacts on regional hydrology and water availability.


“While the overall sea level increase projections in our study are on par with IPCC studies, our results are more detailed and regionally resolved,” says Radic. “This allows us to get a better picture of projected regional ice volume change and potential impacts on local water supplies, and changes in glacier size distribution.”

The IPCC projections estimated sea level rises from mountain glacier and ice cap melt from the between seven and 17 centimetres by the end of 2100. Radic’s projections are only slightly higher, in the range of seven to 18 centimetres.

The study excluded projections related to glacier calving. “Incorporating calving into the models of glacier mass changes on regional and global scale is still a challenge and a major task for future work,” said Radic.

Global Glacier retreat montage as found on Youtube:


In New Zealand the Fox Glacier is in retreat (see photo above taken 2007). According to E. Linacre and Bart Geerts in Shrinking Glaciers worldwide (1999):

"There appears to have been little change in the length of New Zealand glaciers from 1600 to the later part of the 19th century, but then a substantial loss of ice during the past century. The total volume has shrunk from about 100 km3 to 64 km3. Records of precipitation point to no notable reduction of moisture input, so the recent loss is due to higher temperature increasing the rate of ablation, reckoned as between 0.7 - 1.3 degrees since the late 1800's. On average, the 127 glaciers in the Southern Alps of New Zealand have become 25 percent smaller in area and 38 percent shorter in length since a century ago, receding 13.3 metres annually on average. The retreat of the Fox glacier is quite evident. New Zealand glacier termini now lie about 94 m higher than in 1900, implying a warming by 0.6 K, if the vertical temperature gradient is the customary 6 K/km, approximately. Such reduction is in agreement with the observed global warming.


Sources:
* UBC Science, Mountain Glacier Melt to Contribute 12 Centimetres to World Sea-Level Increases by 2100
* E. Linacre and Bart Geerts, Shrinking Glaciers worldwide (1999)
* Photo Fox Glacier by Andrew Turner (Flickr) Creative Commons Attribution licensed