Figure 4: Simulated mass balance and ice volume changes.

(a) Simulated mass balance and (b) simulated ice volume change in the central Southern Alps between 1972 and 2011 for the five largest glaciers within our model domain (from the ‘standard run’). Mass balance units are metres of water equivalent per year (m w.e.a⁻¹). (a) All glaciers show significant interannual variability in glacier mass balance, with positive years in the mid-1980s, early to mid-1990s and mid-2000s. Mass balance at Fox, Franz Josef and Hooker glaciers was more positive overall, while mass balance of Tasman Glacier remained negative except for a few years in the 1990s. Murchison Glacier mass balance stayed negative for the entire period. Note that the mean mass balance for all glaciers (black line) is identical to that shown in Fig. 9 (standard run, all glaciers). (b) The lower panel shows how the cumulative effect of mass balance fluctuations results in glacier volume change for five glaciers in our model domain. Fox and Franz Josef glaciers gained volume overall, consistent with observations that they advanced between 1983 and 2008. Tasman and Murchison glaciers lost volume, again consistent with observations.