Impacts of climate change on glaciers, snow and ice in high mountain regions
The majority of mountain glaciers are losing mass in response to climate change. Most glaciers have been shrinking since the end of the Little Ice Age around 150 years ago. However, since the beginning of the 1980s the rate of ice loss increased substantially in many regions, concurrent with an increase in global mean air temperatures. Glaciers might disappear from some mountain regions by the end of the 21st century given the current melting rate. At the same time, some glaciers have increased in size since the 1980s. This is consistent with regionally increased precipitation in a warming world.
Glaciers originate from accumulations of snow and ice and flow down the slope in response to gravitational forces, and grow or shrink as a result of exchang- es of mass and energy. Glaciers gain mass mainly by snowfall, and lose mass mainly by melting in their lower reaches. Where glaciers terminate in lakes or the sea, significant mass losses can occur by iceberg calving. The difference between mass gains and losses, measured over one year, is known as the annual mass balance. Measuring mass balance is the primary quantitative way of mea- suring the effects of climate change on glaciers. Prior to 1976, however, such measurements are only available for the Northern Hemisphere with emphasis on Europe. Length change measurements provide an important supplement to mass balance measurements, showing intermittent periods of re-advancing glaciers but an overall global and centennial negative trend (Fig 1.)
Compilation of available data (Fig. 1) shows that most mountain glaciers are losing mass, and that the overall rate of mass loss has increased in the last decade. For the last decade the highest mass loss per unit area has been ob- served in the European Alps, Patagonia, Alaska, and north-western USA/south- western Canada (Kaser et al., 2006, Lemke et al., 2007, Arendt et al., 2009).
Figure 1: Cumulative glacier mass balances for seven mountainous regions. Modified from Kaser et al. (2006) and Lemke et al. (2007).
Glacier cumulative mass balance Metres of water equivalent
0 5
-5
-10 -15 -20 -25 -30 -35 -40
1960
Arctic Europe Andes
Asia High Mountains Northwest USA and Southwest Canada
Alaska and Coast Mountains Patagonia
1970 1980 Source : Dyurgerov and Meier, 2005. 11 1990 2000 2003
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