By Mauri S. Pelto
19 July 2014
(Glacier Cnange) – The World Glacier Monitoring Service (WGMS) record of mass balance and terminus behavior (WGMS, 2013) provides a global index for alpine glacier behavior. Mass balance was -638 mm in 2012, negative for the 22nd consecutive year. Preliminary data for 2013 from Austria, Canada, Nepal, New Zealand, Norway, and United States indicate it is highly likely that 2013 will be the 23rd consecutive year of negative annual balances. The loss of glacier area is leading to declining glacier runoff, since globally 370 million people live in river basins where glaciers contribute at least 10% of river discharge on a seasonal basis (Schaner, et al., 2012).
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. The worldwide retreat of mountain glaciers is one of the clearest signals of ongoing climate change (Haeberli, et al., 2000). The retreat is a reflection of strongly negative mass balances over the last 30 years (WGMS, 2013). Glacier mass balance is the difference between accumulation and ablation.
The cumulative mass balance loss since 1980 is 14.9 m w.e. the equivalent of cutting a 16.5 m thick slice off the top of the average glacier (Figure 1). The trend is remarkably consistent from region to region (WGMS, 2011). WGMS mass balance results based on 30 reference glaciers with 30 years of record is not appreciably different, -15.1 m w.e. The decadal mean annual mass balance was -198 mm in the 1980’s, -382 mm in the 1990’s, and -740 mm for 2000’s. The declining mass balance trend during a period of retreat indicates alpine glaciers are not approaching equilibrium and retreat will continue to be the dominant terminus response. The recent rapid retreat and prolonged negative balances has led to some glaciers disappearing and others fragmenting. [more]