Modelling the mass balance of northwest Spitsbergen glaciers and responses to climate change

An energy-balance model is used to calculate mass balance and equilibrium-line altitudes (ELAs) on two northwest Spitsbergen glaciers, Austre Broggerbreen and Midre Lovenbreen, whose mass balances are at present negative, and for which greater than 20 year records of mass-balance data are available. The model takes meteorological data, ice-mass area distribution with altitude, and solar radiation as inputs. Modelling uses mean daily meteorological data from a nearby weather station, adjusted for altitude. Average net balances modelled for 1980-89 using models tuned to the decade's average were -0.44 and -0.47 mw.e. for Lovenbreen and Broggerbreen, respectively, compared with the measured averages of -0.27 and -0.36 m. Sensitivity tests on glacier response to greenhouse warming predict a net balance change of -0.61 m year(-1) per degrees C temperature rise relative to today, and a rise in ELA of 90 m degrees C-1. Modelling of Little Ice Age conditions in Spitsbergen suggests that a 0.6 degrees C cooling or a precipitation increase of 23 % would yield zero net mass balance for Lovenbreen and that further cooling would increase net balance by 0.30 m year(-1) degrees C-1. Set in the context of similar modelling of southern Norwegian, Alpine and Greenland ice masses, these results support the suggestion that glaciers with a maritime influence (i.e. higher accumulation) are most sensitive to climate change, implying a gradient towards decreasing sensitivity as accumulation decreases eastward and with altitude in Svalbard.