PERS_May2014_Flipping - page 388

May 2014
as significantly impacted. As an example, in the Cordillera Blanca
mountain range in Peru, it is anticipated that dry season discharge
rates in some valleys will be reduced by up to 70% compared to
pre-warming flow rates (Baraer et al., 2012). The change in
surface water flow has substantial implications for maintaining
sustainable water supplies for societal needs (Figure 3).
The process of melting leading to changes in river flow rates
could be accelerated if the temperature change coincides with an
increase in black carbon deposited on glacier. Albedo
changes mean that glaciers with high amounts of black
carbon would melt faster, resulting in peak discharge
rates being reached sooner than without black carbon.
River flow reduction would come sooner as glacier area
and volume are reduced more rapidly due to added
black carbon. These events have clear implications
for human use of increasingly scarce water resources.
Better predictive tools for factors affecting glacier melt
rates are urgently needed for planning for climate
change adaptation.
Black carbon particles are generally produced through
incomplete combustion of fossil fuels or biofuels.
Sources of black carbon include smoke from cook
stoves, diesel engines, and biomass burning. Black
carbon particles in and on snow and ice reduce solar
albedo. Black carbon particles efficiently absorb
solar radiation, which leads to localized increased
temperature, which in turn accelerates sublimation
or melting. Simulations have shown that the effect
of black carbon on glacier surfaces can lead to glacier
recession even when temperature and precipitation
records suggest that glaciers should be advancing
(Painter et al., 2013).
While there are numerous reasons why it is difficult
to use remote sensing for black carbon measurement on
snow (Warren, 2013), a number of these uncertainties
are less significant for glacier studies. The albedo of
snow and ice packs can be calculated using radiative
transfer techniques and these calculations clearly show that
snow albedo is reduced by black carbon. With 30 ng/g of black
carbon (a typical North American snow value), the albedo of snow
is decreased between 2.5-6.0% (Warren and Wiscombe, 1985).
The uncertainties are due to the assumptions necessary in the
radiative transfer models, but some of these uncertainties are
reduced when only tropical glaciers are considered.
Figure 3. A comparison of Landsat images from 1975 and 2010 showing glacial
retreat in the Cordillera Blanca.
The change in surface
water flow has substantial
implications for maintaining
sustainable water supplies for
societal needs.
Figure 4: Dark layers of accumulated impurities are indicated on the crevasse
wall. ACSP director, John All, is approximately two meters in height for scale.
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