Modelling regional- and global-scale glacier volume changes over the last millennium

We demonstrate modelling of regional- and global-scale volume changes in glaciers over the last millennium with the Open Global Glacier Model (OGGM) - a glacier geometry and surface mass balance model in active development - using reconstructed climate data timeseries from a set of 6 GCMs. The goals are: 1) to better understand how well different longer-term (extending back to the pre-industrial period) climate datasets perform specifically in terms of their impact on glaciers; 2) to analyse the ability of OGGM to model glaciers over longer timescales while still capturing observed changes over the period of instrumental record; and 3) to determine which regions are better or worse suited to this type of modelling on large scales. A secondary goal is to understand the relative impact of precipitation and temperature - the two primary climate variables used to drive OGGM - on regional glacier volume over this time period, using synthetic climate inputs which isolate long-term trends from each variable individually. Modelling over this last millennium timescale is important due to the preponderance of available instrumental data being much more recent, with glacier models developed and calibrated using data that are mostly recorded in a period of pronounced global glacier retreat. Modelling periods that include both recent warming (and associated observed glacier retreat) and the preceding period that is without such globally coherent changes in climate provides a valuable test of glacier models, to ensure they can generate both relative stability in glacier geometry in stable climates with realistic variability and subsequent reduction in ice mass where appropriate in response to clearer recent temperature trends.