June 29, 2011

BAMS State of Climate 2010-Glacier Chapter

Posted by Mauri Pelto

Published June 2011
Below is the chapter that I author on Alpine glacier and ice sheets. The full BAMS report is an invaluable resource for understanding the climate of 2010 and how it fits into the context of climate change and recent climate. The editorial process is rigorous. The picture below is of Lemon Creek Glacier in Alaska, one of the glaciers discussed.
g. Land surface properties
1) Alpine glaciers and ice sheets—M. S. Pelto
The World Glacier Monitoring Service (WGMS) record of mass balance and terminus behavior(WGMS 2008; WGMS 2009) provides a global index for alpine glacier behavior. Mass balance was negative in 2009 for the 19th consecutive year. Preliminary data for 2010 from Austria, Greenland, Italy, Norway,New Zealand, and the United States indicate it is highly likely that 2010 will be the 20th 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 signalsof ongoing climate change (Haeberli et al. 2000). The retreat is a reflection of strongly negative mass balances over the last 30 years (WGMS 2008). Glacier mass balance is the difference between accumulation and ablation. A glacier with a sustained negative balance is out of equilibrium and will retreat. The recent rapid retreat has led to some glaciers disappearing (Pelto 2010).

The cumulative mass balance loss of the last 30 years is 12.3 m w.e., the equivalent of cutting a 14 m thick slice off the top of the average glacier (Fig. 2.60). The trend is remarkably consistent from region to region (WGMS 2009). WGMS mass balance results based on 30 reference glaciers with 30 years of record are not appreciably different from the results for all reporting glaciers. The decadal mean annual mass balance was -198 mm in the 1980s, -382 mm in the 1990s, and -654 mm for 2000–09. 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 2010 winter accumulation on Austrian and Italian glaciers was about average, and summer temperature was above the mean in 2010. The result was mass losses on glaciers in the Alps: Sonnblickkees, Austria, -790 mm; Ciardoney, Italy, -830 mm; and Fontana Bianca, Italy, -130 mm. The Swiss Glacier Monitoring Network reported that in 2010 the termini of 86 glaciers were in retreat, six were stationary, and three advanced. In Norway, terminus fluctuation data from 30 glaciers for 2010 indicate 27 retreating, one stable, and two advancing. The average terminus change was -17 m, compared to -183 m in 2009. Mass balance surveys found deficits on all Norwegian glaciers. Winter 2009/10 was cold but with little snow on the glaciers, 50%–80% of the long-term normal. Summer was warmer than normal in the south and a bit colder than normal in the north. (L. Andreasson 2011, personal communication).

In the North Cascades, Washington (M. Pelto 2011, personal communication), a transition from El Niño to La Niña conditions led to equilibrium mass balances. El Niño winter conditions led to reduced winter snowfall. La Niña conditions developed by summer causing low summer melting, which offset the low accumulation. The result was positive annual balance on four glaciers, negative balance on five glaciers, and an equilibrium balance on one glacier. All 33 glaciers observed retreated in 2010. In southeast Alaska, snowlines were 50 m above average on Lemon Creek and Taku Glacier of the Juneau Icefield indicative of moderate negative balances. In New Zealand, El Niño led to normal to below normal temperatures through summer and into fall 2010, leading to snowlines in a near steady state (J.Hendrikx 2011, personal communication). On 50 glaciers surveyed, the average snowline was at the equilibrium snowline elevation, after two strongly negative years in 2008 and 2009.

For information on 2010 ice melt on the Greenland ice sheet and in Antarctica please refer to sections 5f and 6e, respectively.

Fig. 2.60. The (top) annual mean and cumulative annual mean balance and (bottom) decadal mean cumulative
specific mass balance (mm w.e.) reported for the 30 reference glaciers to the WGMS.