Spørteggbreen, western Norway, in the past, present and future: Simulations with a two-dimensional dynamical glacier model

A two-dimensional shallow ice-flow model, yielding the glacier geometry at selected time intervals, is used to simulate the development of Spørteggbreen (1) from 8000 cal. yr BP to the present, (2) from ad 2011 to 2050, and (3) extending forward in time to ad 2100 and 2200. Glacier-surface geometry, subglacial topography, mass-balance data, internal deformation, and subglacial sliding are used as input data for the model runs. To force the model from 8000 cal. yr BP to the present, a mass-balance series based on the equilibrium-line altitude (ELA) variations on Jostedalsbreen to the west of Spørteggbreen is applied. A 50% reduction of the ELA amplitude at Jostedalsbreen is used to construct a new mass-balance series, and it was found that this gives a reasonably good coherence between the modelled and the real glacier. The modelled time series for ELA and length changes indicate that the glacier melted away c. 7300 cal. yr BP and was absent for c. 1700 years. It reformed c. 5400 cal. yr BP because of a modest lowering of the ELA and continued to grow in areal extent after c. 4000 cal. yr BP, apart from a small retreat episode c. ad 500. Simulations of the extent and geometry of Spørteggbreen in the future are carried out using different climate scenarios, involving summer temperature and winter precipitation. The model simulation from ad 2011 to 2050 gives relatively minor changes for glacier-surface profiles and glacier-surface geometry, mainly because of the short duration of the model run and because the increase of 12% in winter precipitation compensates for about 25% of the temperature increase of 1.3°C. The simulations from ad 2011 to 2100, and further extended to ad 2200, show, however, significant changes in the glacier volume. This is reasonable because a summer temperature rise of 2.3°C, which is used in this simulation, must be compensated for by an increase in winter precipitation of about 70% to maintain equilibrium.