Response of glaciers to climate change : Mass balance sensitivity, sea level rise and runoff

Sammanfattning: The purpose of this study is to enhance our understanding of the response of glaciers to climate change. Global sea level is affected by changes in glacier ice volume, and melt-water from glaciers is a principal water source in many regions. This study applies glacier mass balance modelling, with varying complexity and spatial resolution, ranging from individual glaciers to regional and global assessments of glacier mass losses. Glaciers located in maritime environments generally show considerably higher mass balance sensitivities than those in continental settings. On average, an assumed increase in annual precipitation of +10% tends to offset the effect of an annual temperature change of +1 K, by roughly 20%. Two case studies, at Storglaciären, Sweden, and Hofsjökull, Iceland, involve model results of future mass balance change and glacier melt induced changes in runoff. Applying a temperature and precipitation scenario for Iceland in 2050 results in increased total runoff from Hofsjökull by roughly one third, and results emphasize the role of the firn layer in delaying water flow through glaciers, yielding a redistribution of discharge within the year. Based on a global gridded data set of glacierized area, the sea level equivalent from all mountain glaciers and ice caps outside the ice sheets in Greenland and Antarctica during 1961–2004, caused by changes in temperature and precipitation, is estimated to be 0.58±0.34 mm a–1. The mountain glaciers and ice caps around Antarctica alone contribute almost 40% of the global estimate, and hence their contribution is considerably larger than previously assumed.