气候变化领域集成服务门户

The maximum 'Little Ice Age' (LIA) glacier extent provides a significant baseline to assess long-term glacier change and to place currently observed rates of glacier recession in a broader temporal context. To that end, we examine the evolution of the plateau icefield Hardangerjokulen since the LIA. First, we reconstruct Hardangerjokulen's maximum LIA extent (similar to AD 1750) and subsequent recession based on the glacial landform record and aided by historical map interpretation. Ice-marginal moraines, glacial drift limits, trimlines, and identifiable erosion and weathering boundaries provide evidence of a LIA icefield with an area of 110 km(2). Existing LIA model simulations of Hardangerjokulen are not yet fully able to reproduce our reconstructed extent. Second, we compile a set of remotely sensed icefield outlines from successive time points in the 20th and 21st century to calculate icefield area and length change since the LIA. This reveals a substantial reduction in icefield size, with a total area loss of 41 km(2) (37%; 2% 10 a(-1)) by 2010 and a cumulative frontal retreat averaging 1.3 km (29%; 5 m a(-1)) by 2013. Icefield recession has been greatest since the end of the 20th century, when rates of areal shrinkage increased to 6.5-10% 10 a(-1) in 1995-2010, and the rate of average terminus retreat accelerated to 17 m a(-1) in 2003-2010. Third, we present a relative dating approach, based on the known age of the different icefield outlines, that allows bracketing ages to be assigned to all ice-marginal landforms between any two outlines. This approach shows that episodes of moraine formation vary temporally between individual outlet glaciers of Hardangerjokulen, suggesting that the moraine record of a single outlet glacier alone may not be sufficient to derive an icefield-wide picture of past ice advances, and thereby climate fluctuations.