Modelling the climate sensitivity of Storbreen and Engabreen, Norway

Abstract

In this report we have modelled the mass balance of two Norwegian glaciers using two different approaches. At Storbreen, a continental glacier in southern Norway, a simplified energy balance model was used. At Engabreen, a maritime glacier in northern Norway, a degree day model was used. Both glaciers have long term mass balance series, detailed topographic maps, micro-meteorological data and nearby meteorological stations outside the glacier. The models have been calibrated with micro-meteorological data from the glacier (Storbreen only), and by traditional mass balance measurements. Downscaled climate scenarios were used to predict the future climate for the two glaciers. Results from the atmosphere-ocean general circulation models ECHAM4/OPYC3 developed at the Max Planck Institute and the HadAm3H developed at the Hadley Centre were used. Assumptions about future greenhouse gas emissions were based on the IPCC SRES B2 scenario. The period 1961-1990 was used as control climate and for the future climate the time slice 2071-2100 was used. The downscaled climate scenarios show a mean temperature increase between the two periods of between 2.2 and 3.3 K for Storbreen and between 2.3 and 2.7 K for Engabreen. The precipitation is predicted to increase by 3-23 % for Storbreen and between 7 and 48 % for Engabreen. The climate sensitivity was calculated by combining calculated Seasonal Sensitivity Characteristics and normalised and smoothed seasonal scenario values. This resulted in a mean temperature sensitivity of Storbreen and Engabreen of -0.50 and -0.90 m w.e. respectively for a 1K warming. A 10 % increase in precipitation represents a climate sensitivity of +0.17 m w.e. for Storbreen. For Engabreen the sensitivity varies between +0.51 and +0.38 m w.e. using the Max Planck and the Hadley scenario respectively. Based on the climate change scenarios and the calculated static climate sensitivities, we estimate that Storbreen will have lost about 30 % of its volume by around 2050. The volume estimates of Engabreen range from a 4 % increase by 2100 (using the MaxPlanck scenario) to a 30 % decrease within 2056 (using the Hadley scenario). The extra annual run-off will be larger from Engabreen than Storbreen due to its much bigger size, by 2050 it will be in the order of 4 mill. m3 water from Storbreen and 50 mill. m3 water from Engabreen.