Glacier and Ice Cap Assessments

2014 Glacier Assessment


Aaron Letterly
Cooperative Institute for Meteorological Satellite Studies, University of Wisconsin, Madison, WI, USA
05 July 2015

Glacial changes typically occur over long periods of time, but observable changes in glacier mass and movement have occurred in periods as short as a decade. Glaciers are especially sensitive to changes in the regional climate (Kuhn et al., 1999). Mass records going back decades and recent, intensive remote sensing of glaciers form the basis of comparison and scientific study. Reactions of glaciers to climate change are complex and delayed, but techniques such as mass balance monitoring as well as the mapping of changes in glacial tongues offer some insights about the changing terrestrial cryosphere.


Global Glacier Mass Balance


2014 saw a continuation of the worldwide long-term trend of negative glacial mass balance (Figure 1). More than 120 glaciers were studied in 2012/13, 37 of these being reference glaciers undergoing continuous observation going back to 1980. The most recent data from the World Glacier Monitoring Service (WGMS) for 2013/2014 shows that preliminary (not yet finalized) mass balance values for 24 out of 27 reporting reference glaciers were negative, with the French Sarennes Glacier and the Alaskan Wolverine Glacier losing 1.9 and 1.8 [m w.e.], respectively. Though not a record-breaking year for specific mass balance changes, preliminary estimates for reference glaciers in 2014 placed sixth in terms of mass decreases, and represents the 31st consecutive year of negative glacial mass balance. This strongly negative annual mass balance corresponds with above average Northern Hemispheric temperatures in 2014.

Figure 1
Figure 1: Annual glacier mass balance (mm w.e.) for all monitored glaciers, worldwide. The dark blue area is the total number of surveyed glaciers for a year, while the yellow bars represent the number of reporting reference glaciers for that year. The orange line shows the reference glacier mean, and the purple line shows the mean of all glaciers. Data is from the World Glacier Monitoring Service.

The 37 reference glaciers span five continents (Australia and Africa are excluded), where each individual glacier has its yearly mass reported to the World Glacier Monitoring Service by a team of independent researchers. Though Figure 1 shows minor year-to-year variation, the trends of mean specific mass balance of the reference glaciers and all reported glaciers over the last 30+ years are very similar.


2014 North American Glacial Mass Balance


In 2014, glaciers throughout North America experienced decreases in vertical thickness, which is related to water equivalent. Across Alaska and Western Canada positive surface temperature anomalies throughout the year may have further enhanced melting. Helm Glacier in British Columbia has lost over 30% of its volume in 25 years, and this trend is not uncommon across the Pacific Northwest and Northern Canada (Molnia 2007).

Figure 2
Figure 2: Cumulative changes (m w.e.) for North American Glaciers since 1984. Data is from the AGU blog, “From a Glacier’s Perspective”, courtesy of Mauri Pelto..

Greenland Glacial Tongue Changes


Much of the ice mass lost each year from Greenland is discharged as marine-terminating outlet glaciers, which slowly detach from the Greenland ice sheet and slide into the ocean. The positions of these glacial fronts, also known as tongues, can indicate recent mass and extent changes for a given glacier. A glacial tongue that extends further into the ocean can be caused by greater accumulation atop a glacier, while a receding tongue indicates that a glacier is not able to replace its lost ice mass due to runoff each year. Where melting is enhanced, glacial tongues tend to recede to higher elevations away from their outflow regions. In 2014, the majority of the Greenland coastline, especially the northwestern and western regions, experienced year-round losses of ice mass. Figure 3 shows total mass changes changes in water equivalent melting throughout 2014.

Figure 3
Figure 3: Total change in mass of Greenland Ice Sheet (relative to 2006) in 2014. Data is based on monthly gravity changes from the GRACE satellite (bottom plot, in gigatons). Data and imagery are from the Polar Portal. They are processed using algorithms from Barletta et al. 2013.

Satellite imagery can be used to remotely monitor the changes in glacial tongue locations multiple times each month. Several years of satellite imagery may be compared to determine the relative position of a glacial tongue, and may thereby provide information about the mass balance of the glacier in that melting season. Figure 4 details the changes in glacial tongue position for three glaciers in different regions of Greenland, as well as their number of melt days in 2014. All images are from September, when outflow glaciers are at their melting terminus.

Figure 4
Figure 4: Relative locations of outflow glacier minimums for Ikertivaq Glacier (1), Humboldt Glacier (2), and Upernavik Glacier (3) in 2014. Images are from the Polar Portal. THistoric overlays of glacier positions are based on Citterio and Ahlstrøm (2013) and Howat et al. (2014).

Compared to the western and northern coasts, however, the lower number of melting days at Ikertivaq Glacier in Southeast Greenland left the outflow terminus very close to 1980 and 2000 values. This lack of melting may stem from the decreased number of summer melting days in that region. Western and Northwestern Greenland, however, experienced significant decreases in minimum tongue extent. The Humboldt Glacier retreated further than historic 2000 extents in multiple areas, which may have been caused by nearly 30 additional melting days in the summer near that region. Upernavik Glacier was also situated among positive melting day anomalies, and decreases in terminus extent were available in three separate zones within the glacier.


References


Barletta, V.R., Sørensen, L.S., and Forsberg, R. (2013): Scatter of mass changes estimates at basin scale for Greenland and Antarctica. The Cryosphere, 7, p. 1411-1432.

Citterio, M. and AhlstrØm, P. (2013): Brief Communication “The aerophotogrammetric map of Greenland ice masses.” The Cryosphere, 7, p. 445-449.

Howat, I. M., Negrete, A., and Smith, B. E. (2014): The Greenland Ice Mapping Project (GIMP) land classification and surface elevation datasets, The Cryosphere Discuss., 8, p. 453–478, doi:10.5194/tcd-8-453-2014.

Kuhn, M., Dreiseitl, E., Hofinger, S., Markl, G., Span, N. and Kaser, G. (1999): Measurements and models of the mass balance of Hintereisferner. Geografiska Annaler A81 (4): p. 659–670.

Molnia, B. (2007): Late nineteenth to early twenty-first century behavior of Alaskan glaciers as indicators of changing regional climate. Global and Planetary Change, 56, p. 23-56.

WGMS (2008): Global Glacier Changes: facts and figures. UNEP/UNESCO/WMO, World Glacier Monitoring Service, Zurich: 73 pp.

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