The ice cap Hardangerjøkulen in the past, present and future climate

Abstract

The relation between glacier behaviour and climate needs to be understood to assess the response of glaciers to changes in climate and the resulting effects on local to global scales. This thesis discusses the changes of the ice cap Hardangerjøkulen in southern Norway related to the past, present and future climate. Hardangerjøkulen receives large snow amounts in winter but also experiences high melt rates in summer and is therefore expected to be sensitive to climate change. The local climate was studied by analysing a six-year meteorological record obtained from an automatic weather station (AWS) on one of the outlet glaciers of the ice cap. Net radiation is found to be the dominant contributor to melt energy, although the turbulent fluxes are also important in the windy and humid climate on this ice cap. The AWS-record from Hardangerjkulen was compared to measurements from an identical AWS on Storbreen, a glacier at a 120 km distance from the ice cap. The temporal variations in meteorological conditions and surface energy fluxes at the two locations are generally highly correlated. The absolute values show important differences: the melt rate is higher on Hardangerjøkulen, mainly due to higher wind speeds. Based on the data from the AWS and long-term mass balance measurements, a spatially distributed mass balance model was developed for Hardangerjøkulen. This model was coupled to an ice-flow model, to evaluate changes in the ice cap geometry resulting from climate variations. Driven with meteorological observations from synoptic weather stations, the coupled model could reproduce the observed evolution of Hardangerjøkulen in the 20th century. The response of the ice cap to future climate warming was investigated for a range of climate projections. For the most probable temperature increase of 3 degrees Celsius, Hardangerjøkulen is bound to disappear around the year 2100. Simultaneous changes in precipitation or other meteorological variables cannot compensate the large volume decrease, the disappearance of the ice cap is only retarded. The results obtained for Hardangerjøkulen cannot directly be applied to other glaciers in southern Norway. Still, the comparable climate conditions and geometry of the glaciers, and particularly the ice caps, in this region suggest that most of the glaciers in southern Norway probably disappear in the 21st century.