August 22, 2013
The BAMS State of the Climate 2012 has been published. It is the best synopsis of 2012 climate there is. What follows is the section on Alpine glaciers, that I authored, from BAMS.
3) Alpine glaciers—M. S. Pelto
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 2012). Glacier mass balance is the difference between accumulation and ablation. The recent rapid retreat and prolonged negative balances have led to some glaciers disappearing and others fragmenting (Pelto 2010).
The World Glacier Monitoring Service (WGMS) record of mass balance and terminus behavior (WGMS 2012) provides a global index for alpine glacier behavior. Annual mass balance was -766 mm
water equivalent (w.e.) in 2011, negative for the 21st consecutive year. Preliminary data for 2012 from Austria, Norway, New Zealand, Nepal, and the United States indicate it is highly likely that 2012 will be the 22nd consecutive year of negative annual balances. The loss of glacier area is leading to declining runoff; the importance of this is indicated by Schaner et al.(2012) who determined that, globally, 370 million people live in river basins where glaciers contribute at least 10% of river discharge on a seasonal basis.
The cumulative mass balance loss since 1980 is 15.7 m w.e. the equivalent of cutting a 17-m thick slice off the top of the average glacier (Fig. 2.9). 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, -15.5 m w.e. The decadal mean annual mass balance was -198 mm w.e. in the 1980s,
-382 mm w.e. in the 1990s, and -740 mm w.e. for 2000–10. 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.
In 2012, slightly-above-average winter accumulation in the Alps was offset by extreme summer ablation, yielding mass balances that were negative. In Austria, Mullwitzkees had a mass balance of -1461
mm w.e. and Hallstätter Gletscher a mass balance of -1944 mm w.e. (Fischer 2012). The Austrian Glacier inventory in 2011 examined 90 glaciers: 87 were in retreat and 3 were stationary. Average terminus change was -17 m, reflecting the continued negative mass balances of the region. In Italy, a large deposit of World War I ammunition melted out of the glacier on Ago Di Nardis Peak during August 2012. The Swiss Glacier Monitoring Network noted in 2011 92 glaciers retreating, 1 advancing, and 3 stationary. The one advancing glacier had retreated the previous five years. The 2012 data are not complete, but retreat was again dominant.
In Norway, terminus fluctuation data from 25 glaciers for 2012 with ongoing assessment indicate 21 retreating, 2 stable, and 2 advancing. The average terminus change was -12.5 m (Elvehøy 2012). The retreat rate is less than 2011. Mass balance surveys found deficits on all Norwegian glaciers.
In the North Cascades, Washington La Niña conditions during the winter led to a wet winter and a cool and wet spring. Summer was drier and warmer than normal. This led to nearly equilibrium conditions on North Cascade glaciers, with mass balance positive on five glaciers and negative on four glaciers (Pelto 2013). In southeast Alaska, the same La Niña conditions prevailed and led to the highest snow totals in several decades. Glacier snowlines were more than 100 m below average on Lemon Creek and Taku Glaciers of the Juneau Icefield indicative of moderate positive mass balance (Pelto 2013).
In New Zealand, the annual end of summer snowline survey on 50 glaciers found snowlines that were approximately 120 m above the elevation for glacier equilibrium. This indicates strong mass balance losses (NIWA 2012). In Nepal, the International Centre for Integrated Mountain Development measured the mass balance of Yala and Rikha Samba Glaciers in 2012 and found both to be significantly negative (Mishra 2012). Pelto (2012) reported that the extensive inventories are better validated than GRACE (Jacob et al. 2012) for
Himalayan glacier volume change. This conclusion has been confirmed by Bolch et al. (2012).