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updated the projections by using the new Randolph Glacier Inventory (Arendt et al.
2012
).
They modeled volume change for each glacier in response to transient spatially differ-
entiated temperature and precipitation projections from 14 GCMs with two emission
scenarios (RCP4.5 and RCP8.5) prepared for the IPCC AR5. Radi´ et al. (
2013
) arrived at
much higher values than Hirabayashi et al. (
2013
) for the period 2006-2100:
155 ± 41 mm SLE (RCP4.5) and 216 ± 44 mm SLE (RCP8.5), and projected the largest
regional mass losses from the Canadian and Russian Arctic, Alaska, and glaciers peripheral
to the Antarctic and Greenland ice sheets. Although small contributors to global volume
loss, glaciers in Central Europe, low-latitude South America, Caucasus, North Asia, and
Western Canada and USA were projected to lose more than 80 % of their volume by 2100
(Fig.
1
. Note that the region names are adopted from the Randolph Glacier Inventory).
Marzeion et al. (
2012
) applied a similar approach to model global mass balances to
reconstruct the mass changes in the past and project future glacier mass evolution. Fol-
lowing Radi´ and Hock (
2011
), they modeled the surface mass balance of each individual
glacier in the Randolph Glacier Inventory and coupled it with volume-area and volume-
length scaling to account for glacier dynamics. The model was validated by a cross
validation scheme using observed in situ and geodetic mass balances. When forced with
observed monthly precipitation and temperature data, the world's glaciers are recon-
structed to have lost mass corresponding to 114 ± 5 mm SLE between 1902 and 2009.
Using projected temperature and precipitation anomalies for 2006-2100 from 15 GCMs
prepared for IPCC AR5, the glaciers are projected to lose 148 ± 35 mm SLE (scenario
RCP2.6), 166 ± 42 mm SLE (scenario RCP4.5), 175 ± 40 mm SLE (scenario RCP6.0),
and 217 ± 47 mm SLE (scenario RCP8.5). Based on the extended RCP scenarios, glaciers
are projected to approach a new equilibrium toward the end of the twenty-third century,
after having lost 248 ± 66 mm SLE (scenario RCP2.6), 313 ± 50 mm SLE (scenario
RCP4.5), or 424 ± 46 mm SLE (scenario RCP8.5).
Giesen and Oerlemans (
2013
) provided an alternative to the degree-day modeling
approaches and projected global glacier mass changes using a simplified surface energy
balance model. The model separates the melt energy into contributions from net solar radi-
ation (computed by multiplying the incoming solar radiation at the top of the atmosphere by
atmospheric transmissivity and subtracting the part of the incoming radiation that is reflected
by the surface) and all other fluxes expressed as a function of air temperature. The model was
calibrated on 89 glaciers with mass-balance observations, whose mass changes were then
projected in response to A1B emission scenario from 8 GCMs from IPCC AR4. Volume-area
scaling was applied to account for changes in glacier hypsometry. The simulated volume
changes from 89 glaciers were then statistically upscaled to all glaciers in Randolph Glacier
Inventory larger than 0.1 km
2
, resulting in 102 ± 28 mm SLE for the period 2012-2099.
3.3 Model limitations
The models above are subject to large simplifications necessary for operation on global
scales. Transferability of model parameters in time and space is questionable (e.g., Carenzo
et al.
2009
; MacDougall and Flowers,
2011
). In addition, some studies have pointed out
that variations in solar radiation have a significant effect on glacier mass changes (e.g.,
Ohmura et al.
2007
; Huss et al.
2009
). To address these concerns, a better approach than
the generally applied degree-day approach would be to apply a physically based mass-
balance model, accounting for all energy and mass fluxes at the glacier scale (Hock
2005
).
These high-complexity models have been applied successfully on many individual glaciers
worldwide (e.g., Klok and Oerlemans
2002
; Reijmer and Hock
2008
;M ¨lg et al.
2009
;
