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Mountain Glaciers Are at Risk for Extinction

Mark Dyurgerov
Institute of Arctic and Alpine Research
University of Colorado at Boulder

Introduction
Mountain glaciers are the product of climate and part of local, regional and global water cycle and environment. Glaciers are sources of beauty in the mountain landscape and are among the agents forming that landscape. Scientists, tourists and climbers bring observations from all around the world that mountains losing glaciers that affects all sources of fresh-water on land, causes the sea-level rise and makes mountains less attractive, more difficult and less appealing to climb (Meier and Wahr, 2002; Meier et al., 2002; Bowen, 2001).

The long-term changes
The major and worldwide retreat of mountain glaciers has started at the end of Little Ice Age (LIA), since the mid of19s century. Compiled in the Table 1 data summarize the results of change in glacier area, and volume of selected mountain regions from tropics to the high latitudes. One sample of data covers the period from the end of the LIA (ca 1850) till the mid/or end of 20s century. The other period shows the changes from about the mid till the end of 20s century. Both periods reveal that the glacier wastage has been pervasive and global in scale. Glaciers in regions with more maritime climate conditions have experienced larger wastage (e.g., Alps) compare to the dryer and colder and regions (e.g., Altai and high Arctic). The period started at the mid-1950s shows that the wastage increased, specifically in the tropics, in the Alps, and in all mountain regions of North America. Exceptionally strong wastage was observed in some parts of Central Asia (Pamirs, Tien Shan, and Dzhungaria). One of the explanation for increase in wastage is that the amount of summer snowfalls decreased in the mountain ranges where summer precipitation (June-September) constitutes more than 50% of their annual sum (Ageta and Higuchi, 1984, Dyurgerov et al, 1995).

Most recent variability and change
Since 1960s the data of glacier volume change has become available with the annual resolution (Cogley, 2002; Dyurgerov, 2002). These data have been used to analysis of year-to-year fluctuations and trend (Dyurgerov, 2002; Meier et al., 2002). The results of this analysis confirm, in general, global change towards glacier wastage established for the period from LIA till the mid-20s century. In addition to these a new knowledge has been achieved, in particular large inter annual fluctuations and trends. In some regions large changes correspond to a large inter annual fluctuations of mass balance (Fig. 1), such as in Rocky Mountains, South Western Alaska, Kamchatka, northwestern parts of Central Asia. The inter annual fluctuations and trends are much smaller in other regions (e.g., Caucasus, Altai, and Canadian Archipelago, Axel Heiberg Island). Large fluctuation corresponds with a small long-term change (e.g., Kamchatka, Fig. 1c-d). These different spatial and temporal mass balance pattern distribution have been correlated with the fluctuations and change in regional climate (Hodge et al., 1998; McCabe et al., 1999) but the global picture has not been properly modeled and understood. In general, the colder and dryer regions show small fluctuations and small trend with extreme annual values observed in Canadian Arctic and Dry Valley, in the West Antarctica.

We have also learned from high-resolution data analysis that the changes in glacier volume have occurred by several shifts; some authors used stronger definitions, "abrupt changes", e.g., Cao, 1998. The first shift in volume change was observed in the mid-1970s (Cao, 1998; McCabe and Fountain, 1995). At the end of 1980s acceleration in ice wastage has increased and enveloped the other regions, such as Alaska, Rocky Mountains, Caucasus (Dyurgerov and Meier, 2000). Glaciers in tropics have appeared in the state of complete extinction (Kaser and Ostmaston, 2002); about several dozens of years would be enough for their complete disappearance (Thompson et al., 2002). Exceptionally strong ice wastage has been observed in Alaska (Arendt et al., 2002), but these large glaciers may survive over hundreds of years.

Global consequences
Ice melt is an important component of relative sea-level rise (RSL). If current rates of RSL were to last for decades or hundreds of years the socioeconomic effect and environmental consequences would be dramatic (Warrick et al., 1995; Trenberth, 1999). The 2001 Intergovernmental Panel of Climate Change (IPCC) estimate of observed RSL is 1.0-2.0 mm/yr (Church et al., 2001). This is caused partly by negative glacier mass balances (Meier, 1984; Warrick et al, 1995). The globally averaged mass balance can be converted into units of sea-level change (362 km³ of water increases sea-level by one mm). There are many problems in converting mass balances of individual glaciers to RSL (Warrick et al., 1995). The continuous time series of updated results created most recently (Dyurgerov, 2002) is the one of the necessary steps to make such calculations. The area-weighted average annual mass balance changed from -82 mm/yr during the period 1961-1976, to -125 mm/yr during the 1977-87 period and to -217 mm/yr during 1988-98; this is equivalent to a change in the rate of sea-level rise due to glacier wastage from 0.15 to 0.24 to 0.41 mm/yr. For the entire period 1961-1998 glaciers lost a volume equivalent of about 20% of the observed RSL.

Can the previous observations be used to predict RSL?
In general, one would expect higher extreme values of glacier volume loss than the record so far would indicate. Estimating glacier volume change in the future will be made more difficult by the changes introduced into mass-balance records. There will no longer be a homogeneous series of values, which can be extrapolated statistically.

Here there is an attempt made to use observed mass balance time series to predict glacier volume loss at the end of 21-century (Fig. 2). Two globally averaged time series are selected; one is for the period 1961-1988, before the strongest and global-scale shift in glacier regime had occurred, the second time series is from 1988 till 1998 (no mass balance data for global assessment available since that year). The expected glacier volume loss is presented in Fig.2 in terms of RSL. This approach is suggested to add newly observed results to existed long-term time-series in order to refine the forecast made previously.

Conclusion
Mountains are loosing beauty, fresh water inflow to rivers and lakes are decreasing, Ocean is advancing to the Land - all of these are consequences of recent change in climate and glacier wastage.