| Glacier surface mass balance is directly observed on only a few selected glaciers. However,
for quantifying the contribution of glacier mass loss to sea-level rise or mountain hydrology,
regional mass balances are required. Extrapolation of single glacier mass balance series to
several thousand glaciers within a mountain range is not trivial and involves considerable
uncertainties. As mass balances of neighbouring glaciers can differ by a factor of up to four
due to different climate sensitivity, surveyed mass balance glaciers might not be
representative for larger areas. This fact needs to be accounted for in mountain range scale
assessments of glacier mass change.
In this study mass balance and ice volume change series for all glaciers in the European
Alps are derived for the period 1900-2011 based on mass balance and glacier inventory
data. Further, future mass balances are modelled until 2100 using GCM ensembles
based on four IPCC emission scenarios. Uncertainties in the extrapolation of single
glacier mass balance series to the entire European Alps are analyzed and the required
field data basis for deriving mass balance estimates on the mountain range scale is
discussed.
Long-term mass balance series for 50 Swiss glaciers are available from a combination of
field data and modelling for the entire 20th century. These series are complemented with
data for 25 glaciers in Austria, France and Italy provided by WGMS. Outlines of
all glaciers in the European Alps relative to the year 2003 are given by a glacier
inventory.
Extrapolation is performed using (1) arithmetic averaging, (2) glacier hypsometry, and (3)
multiple regression of mass balance with variables describing glacier geometry (e.g. area,
slope etc.). For each individual glacier, area change series are derived, thus allowing the
calculation of mountain range annual ice volume changes since 1900. Future mass changes
are computed by driving a combined model for mass balance and 3D glacier geometry
change with scenario temperature and precipitation. Given the sound field data basis for the
European Alps, multiple regression yields the best results and is used for the extrapolation of
mass balance in this study.
Mean glacier mass balance in the European Alps 1900-2011 was –0.28 m w.e. a-1
corresponding to a total ice volume loss of 92 km3. The glacier mass budget was balanced or
slightly positive in the 1910s and between 1960 to the mid-1980s, and strongly negative in
the 1940s and over the last two decades. Until 2050 mean mass balances are expected to
decrease to –1.3 m w.e. a-1 on average. Modelled glacier area in the European Alps by 2100
corresponds to 4-18% of the glacierized surfaces in 2003 depending on the climate
scenario. |