Glaciers are key indicators of climate change. While the mass balance of a glacier reflects annual weather directly, records of length change (also termed front-position change) can be used for climate change detection on a decadal-to-century time scales. When a glacier advances or retreats its surface area also changes. Remote sensing observations of glacier area are valuable to detect glacier changes for larger regions.
The climate indicators data for glaciers in mainland Norway include:
|ID||Name||Mass balance||Length change||Area|
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Some of the selected glaciers have long time series (more than 20 years) of mass balance or length observations and are selected for the “Norwegian Reference Hydrological Dataset for Climate Change Studies” (Fleig et al., 2013). Mass balance, length change and area data are shown for these glaciers and selected other glaciers. The mass balance and length change measurements have been published annually or biannually since 1963 (e.g., Kjøllmoen, et al. 2011). The data are also reported to the World Glacier Monitoring Service and stored in their databases.
NVE’s glacier surface mass balance series contain annual (net), winter and summer balances (Andreassen et al., 2005; Kjøllmoen et al., 2011). The annual balance is the sum of winter balance and summer balance. Area-averaged values for winter and summer balances are calculated by inter- and extrapolating point measurements of snow density, snow depths and ablation. The data presented here are official values from NVE. The series are categorized as ‘original’ (as published in ‘Glasiologiske undersøkelser i Norge/Glaciological investigations in Norway), ‘homogenized’ (for selected or all years) or ‘calibrated’ (periods are calibrated with geodetic observations). Five of the series (Engabreen, Nigardsbreen, Rembesdalskåka, Ålfotbreen and Hansebreen) have been calibrated for parts of the observation period (Andreassen et al., 2016).
An area-weighted annual mass balance signal reflects a year’s weather directly, however, for longer time series changes in glacier area will also influence the annual balance. Thus, care should be taken when analysing long time series as they may contain effects other than just climate change.
Glacier length change is derived from annual, repeated measurements of distance between the glacier terminus and fixed landmarks. It should be noted that in contrast to mass balance measurements, length change does not require annual measurements to have a continuous series. If one year’s data is absent, length change is derived from two years instead of one, maintaining the cumulative signal. Nonetheless, some of the length change series are discontinuous. This is shown by a red vertical line in the diagram.
Glacier area changes are calculated from detailed glacier maps, and from the NVE/CryoClim glacier area outline data. Data are displayed as tables and illustrations. It should be noted that there will be several uncertainties in the area change assessments since glacier areas are derived from different sources (Landsat, topographic maps or tabular data), often with different snow conditions. Each method has its specific uncertainties and area changes may partly be due to differences in methods, snow conditions or human interpretation rather than real glacier changes. (Andreassen et al. 2008).
Changes in glacier area for mainland Norway
To assess changes in glacier area for larger regions, the Landsat-derived outlines have been compared with digital glacier outlines from topographical main map series of Norway. This has been conducted in several regions in Norway: in Jotunheimen (Andreassen et al. 2008), Svartisen (Paul and Andreassen, 2009), Jostedalsbreen (Paul et al., 2011) and all of Norway (Winsvold et al., 2014). Landsat images can also be used to map previous glacier extent. In a study from a section in Jotunheimen, a Landsat image from 2003 was used together with aerial photos and other information to map the LIA maximum extent and create a LIA inventory (Baumann et al., 2009).
References and further reading:
NVE’s internet pages: www.nve.no/glacier
Andreassen, L. M., H. Elvehøy, B. Kjøllmoen, R. V. Engeset and N. Haakensen. 2005. Glacier mass balance and length variations in Norway. Annals of Glaciology, 42, 317–325.
Andreassen, L.M., F. Paul, A. Kääb and J. E. Hausberg. 2008. Landsat-derived glacier inventory for Jotunheimen, Norway, and deduced glacier changes since the 1930s. The Cryosphere, 2, 131–145. (pdf)
Andreassen, L.M., S.H. Winsvold, F. Paul and J.E. Hausberg. 2012. Inventory of Norwegian glaciers. NVE Rapport 38. (pdf)
Andreassen, L.M., H. Elvehøy, B. Kjøllmoen and R.V. Engeset. 2016. Reanalysis of long-term series of glaciological and geodetic mass balance for 10 Norwegian glaciers, The Cryosphere, 10, 535-552, doi:10.5194/tc-10-535-2016, 2016.(pdf)
Baumann, S., S. Winkler and L.M. Andreassen. 2009. Mapping glaciers in Jotunheimen, South-Norway, during the ‘Little Ice Age’ maximum. The Cryosphere, 3, 231–243. (pdf)
Fleig, A.K. (ed.), L.M. Andreassen, E. Barfod, J. Haga, L.E.Haugen, H. Hisdal, K. Melvold and T. Saloranta. 2013. Norwegian hydrological reference dataset for climate change studies. NVE Rapport, 2. (pdf)
Kjøllmoen, B. (ed.), L.M. Andreassen, H. Elvehøy, M. Jackson and R.H. Giesen. 2011. Glaciological investigations in Norway in 2010. NVE Report, 3. (pdf)
Paul, F. and L.M. Andreassen. 2009. A new glacier inventory for the Svartisen region (Norway) from Landsat ETM+ data: Challenges and change assessment. Journal of Glaciology, 55 (192), 607–618.
Paul, F., L. M. Andreassen and S. H. Winsvold. 2011. A new glacier inventory for the Jostedalsbreen region, Norway, from Landsat TM scenes of 2006 and changes since 1966. Annals of Glaciology, 52 (59), 153–162.
Winsvold, S.H., L.M. Andreassen and C. Kienholz. 2014. Glacier area and length changes in Norway from repeat inventories. The Cryosphere, 8, 1885-1903.(pdf)