Glaciers outside Greenland
M. Sharp1 and G. Wolken2
1University of Alberta, Department of Earth and Atmospheric Sciences
With data contributions from D. Burgess, J. G. Cogley, A. Arendt, S. Luthcke and the Canadian Ice Service
Glaciers and ice caps in Arctic Canada are continuing to lose mass at a rate that has been increasing since 1987, reflecting a trend towards warmer summer air temperatures and longer melt seasons. Ice shelf breakup is another consequence of this trend.
Shrinkage of mountain glaciers and ice caps is one of the major causes of global sea level change (Meier et al., 2007). The area of mountain glaciers and ice caps in the Arctic is over 400,000 km2 – nearly half the global total – and these glaciers were responsible for 50-60% of the sea level rise attributed to wastage of glaciers and ice caps between 1961 and 2004 (Kaser et al., 2006).
The health of glaciers is measured using their annual mass balance – the difference between the amount of mass added to them each year by snowfall, and the amount removed by surface melting and meltwater runoff, and by calving of icebergs. Much of the high Arctic is very dry, with little inter-annual variability in annual snowfall. In these regions, year-to-year variability in mass balance arises mainly from changes in summer temperatures and surface melt rates. In more maritime regions like Alaska, Iceland, and Svalbard, snowfall is higher and more variable, so mass balance variability reflects both summer and winter conditions. In most regions, flow rates of large outlet glaciers that drain into the ocean can change suddenly, resulting in large fluctuations in the amount of mass lost by iceberg calving. As yet, these sudden changes due to ice dynamics are not well-documented, and their linkages with changes in climate are not well understood.
The surface mass balance (snowfall minus meltwater runoff) of around 20 glaciers in the Arctic is measured annually. The Russian Arctic islands are not included in this data set because no measurements are currently being made there. The data that are available show an overall trend of increasing mass loss since the early 1990s (Kaser et al., 2006) that is particularly marked in Alaska and the Canadian Arctic.
For most regions of the Arctic, direct mass balance measurements for 2008-09 are not yet available. Measurements for the 2007-08 balance year are, however, available for 20 Arctic glaciers: three in Alaska, four in Arctic Canada, nine in Iceland, and four in Svalbard (Table G1). They indicate net mass loss from 16 of the 20 glaciers, and net mass gain for two in Alaska and two in Svalbard. Field measurements in Alaska show that 2 glaciers located near the coast had very positive balances (among the 20% most positive recorded since measurements began, due to heavy winter snowfall in 2007-2008) and one in the Alaska Range had a slightly negative balance. Gravity field measurements made with the GRACE satellites show that the regional mass balance for the Gulf of Alaska glaciers was essentially zero in 2007-2008 (Table 1; pers. comm. from A. Arendt and S. Luthcke, 2010). In Iceland, the mass balances were slightly more negative than the average for the 16-17 year record, while in Svalbard they were more positive than the 20-42 year average. The annual mass balances of four glaciers in Arctic Canada were among the three most negative in the 43-48 year period of record, reflecting the impact of a very warm summer in 2008. Consistent with both summer air temperatures and measured melt duration, the annual balances of the four Canadian Arctic glaciers were also very negative in 2008-2009 (2nd most negative balance since 1961 on the Devon Island ice cap; Table G1).
Given the small number of both "mass balance" glaciers and situ meteorological measurements in the glaciated regions of the Arctic, we use data from the NCEP/NCAR Reanalysis to characterize climatic conditions and likely trends in mass balance in these regions. Here, we focus on winter (September-May) snowfall for 2008-9 and 2009-10, and summer (JJA) temperatures in the lower troposphere (700 hPa) for 2009 and 2010 (Fig. G1). Relative to the average for 1948-2008, winter precipitation in 2008-9 was relatively high over southeast Alaska and Iceland, and below average in southwest Alaska and southeast Svalbard. 2009 summer temperatures were unusually warm over southern Alaska, the Canadian Arctic and Svalbard, and unusually cool over Novaya Zemlya and Severnaya Zemlya. These patterns lead us to expect negative glacier mass balances (mass loss) in the Canadian high Arctic and, to a lesser extent southern Alaska and Svalbard in 2008-9, and perhaps near neutral or slightly positive balances (mass gain) in Iceland. Thus 2007-08 and 2008-09 extend a period of increasingly negative annual balances in Arctic Canada that began in 1987.
To provide an independent check on the reliability of the data from climate reanalysis, we used data from the QuikSCAT satellite to determine the length of the summer melt season on larger ice caps across the Arctic (Table G2; Fig. G2). We expect that warmer summers will be associated with longer melt seasons. In 2009, melt seasons were longer than the 2000-2004 average in the Canadian high Arctic (especially on northern Ellesmere Island and Axel Heiberg Island) and Svalbard, and appreciably shorter than the average on Novaya Zemlya and Severnaya Zemlya. This is consistent with the distribution of summer air temperature anomalies from climate reanalysis. However, although summer air temperatures on Baffin Island were above the 1948-2008 average, melt season durations were shorter than the 2000-2004 average. This apparent anomaly probably arises because summers during the 2000-2004 period in this region were generally warmer than the 1948-2008 mean. The demise of QuikSCAT in October 2009 means that we are unable to determine the length of the 2010 Arctic melt season using this data source.
In 2009-10, winter precipitation was above average over Labrador, parts of coastal southern Alaska and Novaya Zemlya, and below average over western Iceland. Summer temperatures in 2010 were unusually warm over Iceland and the Canadian Arctic, but cooler than normal over Novaya Zemlya. On the basis of these climate conditions, it seems likely that the 2009/10 mass balances will have been anomalously positive (relative to 1948-2008) in southern Alaska, Labrador and Novaya Zemlya, but anomalously negative in the Canadian high Arctic and Iceland.
The recent period of warm summers and more negative mass balances in the Canadian high Arctic has been associated with continued breakup of the floating ice shelves that fringe northern Ellesmere Island. This phase of breakup began in 2002, and there were major calving events in 2005 and 2008. In 2010, large new fractures were first detected in the Ward Hunt Ice Shelf in Radarsat-2 images from 7 and 14 August, and breakup of the eastern part of the ice shelf was clearly underway in a MODIS image from 18 August (Fig. G3). By the end of August, some 65-70 km2 of the ice shelf had been lost. Meanwhile, fragments of the ice islands that calved from the Ayles, Serson, Peterson, Ward Hunt and Markham ice shelves in 2005 and 2008 have drifted into the Canada Basin and the Sverdrup and Queen Elizabeth Islands and are beginning to enter the Northwest Passage via Barrow Strait.
Kaser, G., Cogley, J.G., Dyurgerov, M.B., Meier, M.F., and Ohmura, A. 2006. Mass balance of glaciers and ice caps: consensus estimates for 1961–2004. Geophysical Research Letters 33, doi: 10.1029/2006GL027511.
Meier, M.F., Dyurgerov, M.B., Rick, U.K., O'Neel, S., Pfeffer, W.T., Anderson, R.S., Anderson, S.P., and Glazovsky, A.F. 2007. Glaciers Dominate Eustatic Sea-Level Rise in the 21st Century. Science 317, 1064-1067.