The influence of changes in glacier extent and surface elevation on modeled mass balance

Abstract

Abstract. Glaciers are widely recognized as unique demonstration objects for climate change impacts, mostly due to the strong change of glacier length in response to small climatic changes. However, glacier mass balance as the direct response to the annual atmospheric conditions can be better interpreted in meteorological terms. When the climatic signal is deduced from long-term mass balance data, changes in glacier geometry (i.e. surface extent and elevation) must be considered as such adjustments form an essential part of the glacier reaction to new climatic conditions. In this study, a set of modelling experiments is performed to assess the influence of changes in glacier geometry on mass balance for constant climatic conditions. The calculations are based on a simplified distributed energy/mass balance model in combination with information on glacier extent and surface elevation for the years 1850 and 1973/1985 for about 60 glaciers in the Swiss Alps. The results reveal that over this period about 50-70% of the glacier reaction to climate change (here a one degree increase in temperature) is "hidden" in the geometric adjustment, while only 30-50% can be measured as the long-term mean mass balance. For larger glaciers, the effect of the areal change is partly reduced by a lowered surface elevation, which results in a slightly more negative balance despite a potential increase of topographic shading. In view of several additional reinforcement feedbacks that are observed in periods of strong glacier decline, it seems that the climatic interpretation of long-term mass balance data is rather complex.

Analysis of the mass balance time series of glaciers in the Italian Alps

“…Rapid geometric changes may also lead to a nonlinear response of B a to atmospheric changes, at least for some glaciers (Elsberg et al, 2001;Paul, 2010). For example, the multiple regression residuals of the Careser Glacier, which were mostly positive in the 1980s, 1990s and 2000s, became predominantly negative after 2008 (Fig.…”

“…The B a and B s values of different glaciers tend to diverge in years with largely negative mass balance and converge in years closer to equilibrium (1993, 2010Fig. 3).…”

Air temperature variability over three glaciers in the Ortles–Cevedale (Italian Alps): effects of glacier fragmentation, comparison of calculation methods, and impacts on mass balance modeling

“…It regulates the accumulation processes via the snowfall elevation limit and the snowpack metamorphism (which affect redistribution phenomena) and regulates the ablation processes via turbulent fluxes and long-wave radiation. It is also closely related to important feedbacks such as albedo, the mass balanceelevation feedback, and the glacier cooling effect, which changes as glaciers adjust their size in response to climatic fluctuations (Khodakov, 1975;Klok and Oerlemans, 2004;Paul et al, 2005;Raymond and Neumann, 2005;Haeberli et al, 2007;Fischer, 2010;Paul, 2010;Carturan et al, 2013).…”

Decay of a long-term monitored glacier: Careser Glacier (Ortles-Cevedale, European Alps)

“…As one of the few Tier 3 monitoring sites in the world with a 46 yr continuous time series of mass balance measurements (only 22 glaciers worldwide have longer series; Zemp et al, 2009), the Careser Glacier is frequently referred to as an emblematic example of accelerated deglaciation and of vanishing glaciers with long-term mass balance observation series (e.g. Paul et al, 2007;Pecci et al, 2008;Paul, 2010;Gabrielli et al, 2010;. The aims of this work are as follows: (i) to document the variations in length, area and volume of the glacier since 1897; (ii) to update and validate the series of direct mass balance measurements; (iii) to compare the current mass loss rates with secular trends; and (iv) to outline the possible future evolution of the glacier.…”