Historical glacier fluctuations of Jostedalsbreen and Folgefonna (southern Norway) reassessed by new pictorial and written evidence

Abstract

Glaciers are sensitive indicators of past climate and thus valuable sources of climate history. Unfortunately, direct determinations of glacier changes (variations in length and mass balance) did not start with increasing accuracy before the end of the nineteenth century. Therefore, historical and geomorphological evidence has to be used to reconstruct glacier variability for preceding time periods. Here we present new glacier length reconstructions for selected outlet glaciers of Jostedalsbreen and Folgefonna (two ice caps in southern Norway). A wealth of different historical sources (drawings, paintings, prints, photographs, maps, written accounts; about 400 documents) allows reconstruction of glacier length variations for the last 300 (Jostedalsbreen), and 200 years (Folgefonna), respectively. We present historical material newly collected for Briksdalsbreen, Bøyabreen, Store Supphellebreen, Bergsetbreen, Nigardsbreen, Lodalsbreen (all Jostedalsbreen), and Bondhusbrea, Buerbreen (both southern Folgefonna). At Jostedalsbreen, glaciers reached their ‘Little Ice Age’ (LIA) maximum extent around AD 1750. Nigardsbreen is best documented, where also the advance in the mid-eighteenth century can be quantified. However, the nearby Bergsetbreen shows more distinct glacier advances and retreats since the LIA maximum extent. A minor peak is documented in the 1870s for all outlet glaciers of Jostedalsbreen studied. At southern Folgefonna, the LIA maximum was attained in the late 1870s (second peak around 1890). So far, there is no direct historical evidence for the time before AD 1800.