A reconstruction of Jostedalsbreen during the Little Ice Age and geometric changes to outlet glaciers since then.

Mountain glaciers and ice caps are undergoing rapid mass loss but rates of present-day changes and models of future projections both lack long-term (centennial-scale) context. Here, we reconstruct the maximum glacier extent and ice surface of Jostedalsbreen, which is the largest ice mass in mainland Europe, during the Little Ice Age (LIA) ∼ 1740 to 1860. The LIA maximum ice-covered area was 568 km2 and the LIA ice volume was between 61 km3 and 91 km3. We show that the major outlet glaciers have lost at least 110 km2 or 19% of their LIA area and 14 km3 or 18% of their LIA volume until 2006. The largest proportional changes for individual outlet glaciers are associated with the loss of ice falls and consequent disconnection of tributaries. Glacier-specific hypsometry changes suggest a mean rise in ELA of 135 m but there is wide inter-glacier variability. A median date for the LIA of 1755 suggests that the long-term rate of ice mass loss has been 0.05 m w.e. a−1. That long-term rate is virtually the same as modern rates, which contrasts with findings of other studies around the world reporting acceleration of glacier mass loss rates since the LIA. Overall, we highlight the utility of geomorphological-based reconstructions of glaciers for understanding and quantifying long-term (centennial-scale) responses to climate and hence for understanding of meltwater production and proglacial landscape evolution. • Mapping to reconstruct area and volume of glaciers during the LIA. • Spatial analysis of geometric changes to glaciers between the LIA and 2006. • Mean mass balance (unexpectedly) slightly less since 1960s than since LIA. • Spatial patterning of changes suggests hypsometric control. [ABSTRACT FROM AUTHOR]