During the last century glaciers in Norway retreated as glaciers in other parts of the world. However, in the 1990s many Norwegian glaciers advanced as a result of several winters in a row with precipitation above normal. During the last four years, however, Norwegian glaciers have decreased significantly, shrinking both in volume and length. Several consecutive years of little winter precipitation, and record-warm summers in 2002 and 2003, have taken their toll.
Glaciers cover about 1% of the land area in Norway (about 2600 km2). In Norway, 98% of the electricity comes from hydropower, and 15% of the exploited runoff comes from river basins with glaciers. Glaciers are sensitive to climate change, and the Intergovernmental Panel on Climate Change (IPCC) sees them as a key indicator of changes in the global and regional climate.Observations of glacier changes
Systematic measurements of the glacier’s front position and thus the glacier’s change in length started around 1900 in many glacial regions in Norway. The extent of the monitoring program has varied, but it was revitalized in the 1990s when many glaciers started to advance (figure 1). In total, 2200 length observations from 58 glaciers have been made.
The annual mass balance for a glacier is made up of snow accumulation in the winter (winter balance) and melting of snow and ice in the summer (summer balance). The difference between the two is called the net balance. A more detailed description of methods can be found in Kjøllmoen (2004) or Andreassen et al. (2005). The first mass balance observations in Norway were made in 1949 on Storbreen in Jotunheimen (figure 2). The mass balance record for Storbreen is the second longest mass balance series in the world. The number of observed glaciers has varied from year to year. In total, the mass balance has been measured at 42 glaciers (a total of 532 observation years). In South Norway, six of the glaciers have been measured for 42 years or more. These glaciers span from the maritime Ålfotbreen in the west to the continental Gråsubreen in the east.Glacial retreat
Generally speaking, Norwegian glaciers melted in the 20th century. The amount of retreat varied from glacier to glacier, with a maximum of 2.5 km. However, several periods of glacier advance have been registered since the length measurements began around 1900 (figure 1). Inland glaciers have with few exceptions retreated throughout the whole period, while many maritime glaciers have had periods with retreat and advancement. From 1930 to 1990, most glaciers retreated. In the 1990s, many coastal glaciers began to advance. From 2000, there has been a noticeable change in the glaciers in Norway: a rapid retreat has been observed in most glaciers (figure 3).Large difference in mass turnover
Measured net-balance profiles for nine of the glaciers in the period 1989-2003 show the large differences in elevations, variations in the mass balance gradient, and mass turnover among Norwegian glaciers (figure 4). The turnover at the lower parts of Engabreen and Nigardsbreen is large compared to the conditions at the higher elevated glaciers in Jotunheimen (Storbreen, Hellstugubreen and Gråsubreen). The glaciers in the west have a far greater mass turnover than the continental glaciers in the east. Ålfotbreen glacier, which is the farthest to the west, has the largest winter- and summer balances, with mean values for the period 1963-2004 of 3.7 and -3.5 meters of water equivalent (m w.e.), respectively. Mean values for Gåsubreen glacier farthest to the east is much less: the winter balance is only one fifth (0.8 m w.e.), while the summer balance is only one third (-1.1 m w.e.) of the balance at Ålfotbreen. For the coastal glaciers, the winter balance is the most important factor for the net balance, while the continental glaciers are to a greater extent affected by variations in the summer balance.Have the glaciers increased or shrunk?
Figure 5 shows the cumulative net balance for six glaciers in South Norway. The maritime glaciers, Ålfotbreen and Nigardsbreen, have had a considerable growth in the period 1963-2000. The Hardangerjøkulen glacier also advanced in this period, while the continental glaciers (Storbreen, Hellstugubreen and Gråsubreen) shrunk considerably. The large surplus is due to snow-heavy winters in the period 1989-1995, and emphasizes the importance of the winter balance for the mass balance of Norwegian glaciers (especially those close to the coasts). Also the continental glaciers had a temporary advancement in this period. In the period 2001-2003, all of the monitored glaciers in Norway showed considerable retreat. This is due to a combination of winters with little snow and very warm summers, which resulted in record-high glacial melt. Summer 2002 was the warmest on record in Norway, and summer 2003 was the fourth warmest summer since the measurements started in 1876 (source: met.no). The general trend for glacial areas throughout the world has been glacial retreat, and the mass increase of the Norwegian maritime glaciers is unusual in a world context. The most recent development of Norwegian glaciers, however, is more in line with what is happening to glaciers world-wide.Is the specific net balance a climate indicator?
The answer is both yes and no. In the short term, the annual balance, the winter balance, and the summer balance reflect the weather conditions of that year. The specific balance tells whether the glacier lost or gained mass that year. The result of the weather is shown directly on the glacier. Evaluating long time series requires some caution, however, because the geometry and dynamics of the glacier change over time (Oerlemans, 2001). A change in glacier length is considered a proxy signal of climate change (Hoelzle, 2003). How quickly changes in the glacier’s mass will appear on the glacier terminus depend on how steep and long the glacier is, and on the glacier’s mass balance gradient. For example, Nigardsbreen has had a positive mass balance since 1963, but did not start to advance until 1987. The neighboring Briksdalsbreen, which is considerably shorter and steeper, reacted much more quickly to changes and has had several advances and retreats during the same period.What will happen to the glaciers in the future?
Glaciers are sensitive to climate change, and global warming can seriously influence their extent. Glaciers that span a small elevation interval, such as the Gråsubreen and Ålfotbreen, can disappear more quickly than glaciers that have accumulation areas far above the current equilibrium line. Ice caps with flat accumulation areas, such as Hardangerjøkulen and Nigardsbreen, are thus particularly vulnerable if the glacier’s equilibrium line is raised. An increase in global temperatures is projected for the future, but also more precipitation, particularly for the coastal glaciers. This can mean that the glaciers in coastal areas are more likely to survive than the inland glaciers (see also Nesje, 2004). At the time of this writing, it looks like the winter precipitation in 2005 will be a above normal at the glaciers in Norway, in contrast to the previous years. Thus the coastal glaciers may come out ahead.References
- Andreassen, L.M., H. Elvehøy, B. Kjøllmoen, R.V. Engeset and N. Haakensen. 2005. Glacier mass balance and length variation in Norway. Annals of Glaciology, 42. Accepted for publication.
- Hoelzle, M., W. Haeberli, M. Dischl, M. and W. Pescke, 2003. Secular glacier mass balances derived from cumulative glacier length changes. Gl. Plan. Change, 36, 295-306.
- Kjøllmoen, B., ed. 2004. Glaciological investigations in Norway in 2003. NVE Report 4-2004.
- Nesje, A. 2004. Breene i Europa minker. CICEROne 5/2004, 24-26.
- Oerlemans, 2001: Glaciers and climate change. A.A. Balkema Publishers.
Denne artikkelen ble opprinnelig publisert i Magasinet CICERONE nummer 2, 2005