July 12, 2012
Below is the section I wrote on Alpine Glaciers for the BAMS State of the Climate in 2011 published on July, 10, 2012. The focus is on glacier changes in 2011.
3) ALPINE GLACIERS—M. S. Pelto
The World Glacier Monitoring Service (WGMS) record of mass balance and terminus behavior (WGMS 2011) provides a global index for alpine glacier behavior. Mass balance was -766 mm in 2010, negative for the 20th consecutive year. Preliminary data for 2011 from Austria, Norway, New Zealand, and United States indicate it is highly likely that 2011 will be the 21st consecutive year of negative annual balances.
Alpine glaciers have been studied as sensitive indicators of climate for more than a century, most commonly focusing on changes in terminus position and mass balance (Oerlemans 1994). The worldwide retreat of mountain glaciers is one of the clearest signals of ongoing climate change (Haeberli at al. 2000). The retreat is a reflection of strongly negative mass balances over the last 30 years (WGMS 2011). Glacier mass balance is the difference between accumulation and ablation. The recent rapid retreat and prolonged negative balances has led to some glaciers disappearing and others fragmenting (Pelto 2010; Bhambri et al 2011; Shahgedanova et al. 2010).
The cumulative mass balance loss of the last 30 years is 13.6 m w.e. (Fig. 2.14), equivalent to cutting a 15 m thick slice off the top of the average glacier. The trend is remarkably consistent from region to region (WGMS 2011). WGMS mass balance results based on a global dataset of 30 reference glaciers with 30 years of record is not appreciably different, -13.1 m w.e. The decadal mean annual mass balance was -198 mm in the 1980s, -382 mm in the 1990s, and -740 mm for 2000–10. The declining mass balance trend during a period of retreat indicates that alpine glaciers are not approaching equilibrium and retreat will continue to be the dominant terminus response.
In 2011 there was below-average winter accumulation in the Alps and significantly above-average spring and summer temperatures. This resulted in consistently strong negative balances on Austrian glaciers in 2011: Sonnblickkees, -2460 mm; Jamtalferner, -1434 mm; Kesselwandferner, -640 mm; and Hintereisferner, and -1420 mm (Fischer 2012). The Austrian Glacier Inventory examined 90 glaciers. Of these, 87 were in retreat, 3 were stationary, and average terminus change was -17 m, reflecting the continued negative mass balances of the region. In Norway, terminus fluctuation data from 31 glaciers for 2011 indicated 27 retreating, 2 stable, and 2 advancing. The average terminus change was -17.2 m (Elverhoi 2012). The retreat rate closely matched the 2010 rates. Mass balance surveys found deficits on all Norwegian glaciers. In the North Cascades, Washington (Pelto 2011), La Niña conditions and record wet and cool conditions from March to June led to positive mass balances on all 10 glaciers examined. In southeast Alaska, 2011 snowlines were 50 m above average on Lemon Creek and Taku Glacier of the Juneau Icefield, indicative of moderate negative balances.
In New Zealand, observations on 50 glaciers found snowlines that were much higher than normal, indicating strong mass balance losses (NIWA 2011). Summer melt conditions were considerably above average.
In the high mountains of central Asia, detailed glacier mapping inventories, such as from GLIMS (Global Land Ice Measurements from Space) using ASTER, Corona, Landsat, and SPOT imagery, of thousands of glaciers indicated increased strong thinning and area loss since 2000 throughout the region except the Karakorum. In the Russian Altai, mapping of 126 glaciers indicated a 19.7% reduction in glacier area from 1952 to 2004, with a sharp increase in losses after 1997 (Shahgedanova et al. 2010). In Garhwal Himalaya, India, for 58 glaciers examined from 1990 to 2006, area loss was 6% (Bhambri et al 2011). In the Nepal Himalaya area, loss from 1963 to 2009 was nearly 20%, (Bajracharya et al. 2011), and thickness losses increased from an average of 320 mm yr-during 1962–2002 to 790 mm yr-1 during 2002–07 in the Khumbu region, including area losses at the highest elevation on the glaciers (Bolch et al. 2011). In the Tien Shan Range, over 1700 glaciers were examined: from 1970 to 2000, glacier area decreased by 13%, and from 2000 to 2007 glacier area shrank by 4% (Narama et al. 2010). An inventory of 308 glaciers in the Nam Co Basin, Tibet, noted an increased rate of area loss for the 2001–09 period; 6% area loss (Bolch et al. 2010). A new means of assessing global glacier volume is via GRACE (Rodell et al. 2011), which, due to its spatial resolution, is unable to resolve specific changes of individual glaciers or watersheds. In the high mountains of central Asia, GRACE imagery found mass losses of -264 mm yr-1 for the 2003–09 period (Matsuo and Heki 2010). This result is in relative agreement with the other satellite image assessments, but is at odds with another more recent global assessment from GRACE that estimated Himalayan glacier losses at 10% of that found in the aforementioned examples for volume loss for the 2003–10 period (Jacob et al.2012). At present, the detailed inventories are better validated.