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TURN DOWN THE HEAT: CONFRONTING THE NEW CLIMATE NORMAL
Although the conditions in the Southern Andes are very different
(e.g., in terms of climate or sun angle) the trend in glacier
retreat is obvious here as well (Figure 3.15). Lopez et al. (2010)
investigated changes in glacier length in 72 glaciers in the Chilean
Southern Andes (Northern and Southern Patagonian Ice Field
and Cordillera Darwin Ice Field) between 1945–2005, based on
aerial photographs and satellite images (ASTER, Landsat). They
concluded that the observed general trend in glacial retreat is
likely controlled by atmospheric warming. In the Northern Patagonian
Ice Field, glaciers retreated in length by 4–36 percent, in
the Southern Patagonian Ice Field by 0–27 percent, and further
south in the Cordillera Darwin Ice Field by 3–38 percent. However,
glacial length fluctuations provide only limited insight into the
imbalance of glaciers, and the large heterogeneity of glacial retreat
is very much influenced by such local conditions as exposition,
basin geometry, glacier dynamics, and response times.
A different way of measuring glacier mass loss rates is by
space gravimetry (GRACE)—by measuring the changing gravity
field from satellites in regions with large continuous ice extent (a
method available since 2003). For the large ice caps of Northern
Figure 3.15: Ice loss from outlet glaciers on the Patagonian
Ice Field in southern South America since the Little Ice Age.
Source: Glasser et al. (2011), Figure 1.
and Southern Patagonia, Ivins et al. (2011) inferred ice loss rates
of 26±6 Gt per year between 2003–2009, which explains a total
loss of about 154±36 Gt over six years. Jacob et al. (2012) reached
similar estimates using the same technique, with mass balance rates
for the period 2003–2011 of 23±9 Gt per year in the Patagonian
glaciers and of 6±12 Gt per year in the rest of South America
(including the tropical glaciers). However, the spatial resolution
of about 300 km is extremely coarse and difficulties arise in distinguishing
signals from hydrological storage and glacial isostatic
adjustment (Gardner et al. 2013).
Snowpack and Snow Cover Changes
In the tropical glacier region, due to the high solar radiance, with the
sun close to the zenith, albedo appears to be a major determinant
in attenuating the melting process. Consequently, the frequency
and intensity of snowfall plays a major role in determining the net
radiation over the entire year, modulated by wet and dry seasons
(Rabatel et al. 2013). In the subtropical Andes of Chile and western
Argentina, where snowpack has been monitored for more than
50 years (1951–2004), there is no significant trend over this period
(Masiokas et al. 2006, 2012). However, the data display a marked
inter-annual variability ranging from 6–257 percent around the
1966–2004 mean, with a clear influence from the warm phases
of ENSO (El Niño).
Studies about snowpack in the Southern Andes are rare. It
can generally be stated that changes in snowpack extent magnify
changes in the seasonality of the water availability by a reduction
of the flows in dry season and an increase in flows in wet seasons
(Vicuña et al. 2013).
3.4.1.3 Projections of Glacial Change
As the IPCC confirms with high confidence, glaciers worldwide
are out of balance with current climatic conditions. Furthermore,
it is very likely that anthropogenic forcing played a statistically
significant role in the acceleration of the global glacier loss in the
last decades of the 20th century (Bindoff et al. 2013).
Various model projections for different future emissions scenarios
indicate that glaciers will continue to shrink in the future,
even without further temperature increases. Confidence in these
models is supported by their ability to reproduce past observed
glacier changes using corresponding climate observations as forcing.
Model validation is challenging, however, due to the scarcity
of independent observations (currently available for only a small
fraction of well-observed glaciers).
In a 2°C world, Marzeion et al. (2012) expect a reduction in ice
volume of tropical glaciers by 78–94 percent based on the period
1986–2005. This signal is less drastic in the Southern Andes, with
an expected 21–52 percent volume reduction of the 4,700 Gt ice
mass by 2100 for the same warming level. Marzeion et al. (2012)
project the amount of tropical glaciers to be lost in a 3°C world
at 82–97 percent, very similar to the 2°C world scenario. For the
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