Global Warming and its Effect on Snow/Ice/Glaciers
Encyclopedia of Snow, Ice and Glaciers
V. P. Singh, P. Singh, and U. K. Haritashya (eds.)
Springer
Stephen J. Déry
Environmental Science and Engineering Program
University of Northern British Columbia
3333 University Way
Prince George, BC, Canada, V2N 4Z9
E-mail: sdery@unbc.ca
Tel: + 1 250 960 5193
Fax: + 1250 960 5845
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GLOBAL WARMING AND ITS EFFECT ON SNOW/ICE/
GLACIERS
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Synonyms
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Impact of climate change on the cryosphere
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Definition
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Global warming. Rising air temperatures on a global scale.
Global warming and its effect on snow/ice/glaciers. Rising air temperatures on a global scale
that are modifying components of the cryosphere, including snow, ice and glaciers.
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Introduction
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One of the most notable manifestations of global warming is its impact on snow, ice and
glaciers. The cryosphere, defined as the portion of the earth system where water, soils, and
other natural materials occur in the frozen form, is a prominent indicator and integrator of
climate change as a contraction in its spatial extent, volume, and duration is particularly
sensitive to rising air temperatures. Components of the cryosphere such as snow, ice, and
glaciers play a major role in the global climate system through their distinct characteristics
such as their high albedo values that induce strong positive feedbacks on warming (Déry and
Brown, 2007) and their insulating properties that decouple the atmosphere with the
underlying land surface or water (Stieglitz et al., 2003). Further, the cryosphere forms
important and reliable reservoirs of freshwater, contributing water resources to a large
fraction of the global population (Barnett et al., 2005).
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Observational Evidence of Change
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There is mounting observational evidence that global warming is leading to modifications in
the state of the cryosphere. For instance, Déry and Brown (2007) report a 5% decline in snow
cover extent in the Northern Hemisphere between 1972 and 2006 based on satellite
measurements. Brown (2000) reconstructs the snow cover extent data prior to the satellite era
and finds a decreasing trend in Northern Hemisphere snow cover extent over the period
1915-1997. Brown and Braaten (1998) and Curtis et al. (1998) find declining snow depths
across most of Canada and Alaska during the 20th century. Mote et al. (2005) document a
widespread decline in snow mass in the North American Cordillera from 1925 to 2000 in
response to rising surface air temperatures. Ye et al. (1998) report decreasing (increasing)
snow depths in the zonal band 50-60oN (60-70oN) in Eurasia from 1936 to 1983. Stone et al.
(2002) document a 20th century trend toward earlier snowmelt in Alaska whereas Ye and
Ellison (2003) and Vaganov et al. (1999) observe an opposite trend in northern Eurasia.
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Global warming also influences the different forms of ice found in oceans, lakes or rivers.
Observational records point to later freezing (trend of 5.8 days per century) and earlier
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breakup (trend of 6.5 days per century) of lake and river ice across the Northern Hemisphere
from 1846 to 1995 (Magnuson et al., 2000). Sea ice in the Arctic declined in extent by about
3% per decade whereas sea ice in the Antarctic increased spatially by 1.3% per decade over
1978-1996 (Cavalieri et al., 1997). This observed asymetric response of sea ice extent to
global warming is consistent with global climate model (GCM) simulations. The annual
minimum in Arctic sea ice extent, typically reached in mid-September, attained an
unprecedented low value of 4.2 × 106 km2 in 2007 (Maslanik et al., 2007). The rapid retreat
in Arctic sea ice is outpacing all of the scenarios predicted by GCMs (Stroeve et al., 2007).
Submarine measurements reveal a 42% decline in Arctic sea ice draft thickness over a period
of 40 years ending in the 1990s (Rothrock et al., 1999).
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In response to rising air temperatures and changing precipitation regimes, glaciers worldwide
are experiencing a general trend toward negative mass balances (Dyurgerov and Meier, 2000;
Oerlemans, 2005). Regional declines in glacier extent and volume include the Rockies and
Coast Mountains of North America, the Andes of South America, the European Alps and the
Asian Himalayas. Glaciers are particularly sensitive to changes in summertime air
temperatures that drive ablation and wintertime precipitation that forms accumulation. Strong
modifications in either of these seasonal quantities may alter the mass budget of glaciers.
Discharge of ice from outlet glaciers of Greenland doubled in the period 1996-2005 (Rignot
and Kanagaratnam, 2006) while surface melt and ablation expanded to record levels in
response to global warming (Tedesco et al., 2008). In the Southern Hemisphere, global
warming has not affected the overall mass balance of the Antarctic ice sheet owing in part to
its colder environment than the Greenland ice sheet. However, the collapse of the Larsen ice
shelf near the Antarctic Peninsula in January 1995 along with the subsequent acceleration of
ice discharge and calving provide some evidence of a growing importance of climate change
in the area (Rott et al., 1996; Rignot et al., 2004).
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Future projections
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A number of studies have examined the impacts of global warming on the potential future
state of the cryosphere. In general, simulations of 21st century climate by GCMs project
decreases in the spatial extent, volume and duration of many components of the cryosphere.
Frei and Gong (2005) and Déry and Wood (2006) project declines in the extent and duration
of the Northern Hemisphere snow cover. Räisänen (2008) and Déry and Wood (2006) also
report potential reductions in the seasonal accumulation of snow, particularly in the midlatitudes whereas high-Arctic regions may experience increases in seasonal snow mass.
Simulations of the future state of the global climate system project abrupt declines in sea ice
extent and thickness, with the potential of an ice free Arctic Ocean by the middle of the 21st
century (Holland et al., 2006). Rising summertime air temperatures suggest that glaciers may
disappear altogether in the Alps by 2100 (Zemp et al., 2006) and contribute substantially to
rising sea levels (Meier et al., 2007). Enhanced melting of the Greenland ice sheet and
potentially the Antarctic ice sheet will further advance sea level rise (Alley et al., 2005). Thus
global warming is anticipated to contribute to a shrinking cryosphere in the coming decades.
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Repercussions of change
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Changes in the cryosphere have profound environmental, biological and societal
repercussions (Barnett et al., 2005). As an example, mass wasting of glaciers has significant
implications on downstream freshwater resources and hydrological processes. Glacier
recession in western Canada has led to declines and phase shifts in late summer streamflow
(Stahl and Moore, 2006; Déry et al., 2009). This has important ramifications for populated
downstream areas such as the arid Canadian Prairies that are now subject to an impending
water crisis (Schindler and Donahue, 2006). Furthermore, glacier and ice sheet melt
contributes to rising sea levels and potential changes in ocean currents (Alley et al., 2005).
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Modifications in snowpack characteristics also affect ecological processes such as the
duration of the growing season (Vaganov et al., 1999), and on plant productivity, density,
and distribution. Changes in snowpack accumulation influence prey-predator relationships
(Stenseth et al., 2004) and the feeding habits of mountain caribou and other ungulates
(Kinley et al., 2007). The potential collapse in the populations of polar bears in the Arctic
(Durner et al., 2009), emperor penguins in Antarctica (Jenouvier et al., 2009), and other
species forms another potential consequence of a shrinking cryosphere.
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Furthermore, cryospheric changes influence socioeconomic and recreational activities. The
potential opening of the Northwest Passage in the Canadian Archipelago may lead to
increased shipping activity in the high Arctic. Warmer winters have led to shorter periods
with river ice covers in northern Canada, impeding commercial transport on ice roads
(Hinzman et al., 2005). Tourism may suffer from the degradation of glaciers in many regions
including Waterton National Park in the Canadian Rocky Mountains (Scott et al., 2007).
Outdoor recreational activities such as skiing and ice skating may also be curtailed owing to
reduced or unreliable snow/ice packs (Elsasser and Bürki, 2002; Visser and Petersen, 2009).
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Summary
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Rising air temperatures are inducing dramatic changes in the state of the cryosphere. Global
warming has led to a general decline in the presence of snow, ice and glaciers over the past
decades. Future projections of climate suggest that changes in the cryosphere will intensify
and accelerate over the 21st century in response to continued global warming. The
disappearance of snow, ice and glaciers will reduce freshwater storage on the land surface,
leading to diminishing water resources in many areas. Given the increasing demands for
freshwater, changes in the cryosphere driven by global warming may pose serious challenges
to humans and ecosystems in the 21st century.
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Stephen J. Déry
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Cross-references
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Cryosphere
Deglaciation
Depletion of snow cover
Glaciers as indicators of climate change
Impact of snow cover and glaciers on runoff
Lake ice
Retreat/advance of glaciers
Sea ice
Streamflow trends in the mountainous region
Thinning of Arctic sea-ice cover
Thinning of glacier (downwasting)