5.4: Glaciers and ice caps
Canada’s
Arctic and alpine glaciers have thinned over the past five decades due to
increasing surface temperatures; recent mass loss rates are unprecedented over
several millennia (very high confidence). Mass loss from glaciers and ice caps
in the Canadian Arctic represent the third largest cryosphere contributor to
global sea level rise (after the Greenland and Antarctic ice sheets) (very high
confidence).
Under a
medium emission scenario, it is projected that glaciers across the Western
Cordillera will lose 74 to 96% of their volume by late century (high
confidence). An associated decline in glacial melt water supply to rivers and
streams (with impacts on freshwater availability) will emerge by mid-century
(medium confidence). Most small ice caps and ice shelves in the Canadian Arctic
will disappear by 2100 (very high confidence).
Canada’s
landmass supports approximately 200,000 km2 of ice, which includes glaciers and
ice caps in western Canada, the Canadian Arctic Archipelago (CAA), and northern
Labrador (Radic et al., 2014; Clarke et al., 2015). These glaciers are
responding to long-term climate changes since the Little Ice Age, as well as
the anthropogenic rapid warming of recent decades. The largest ice caps are
located in Queen Elizabeth Islands and Baffin Island of the Canadian Arctic.
Because they drain to the Arctic Ocean, these ice caps represent the greatest
potential contribution from Canadian territory to sea level increases (Radic et
al., 2014). Mountain glaciers of western Canada cover a much smaller area and
have less potential to affect global sea levels. However, they are an important
source of meltwater runoff, as melt from these glaciers is a significant
contributor to summer streamflow in river systems (Jost et al.,, 2012; Naz et
al., 2014; Bash and Marshall, 2014). The loss of mountain glaciers can
therefore influence how much water is available, and when, in downstream areas
that can extend far from the source regions.
A key
measure of health for glaciers and ice caps is surface mass balance, the
difference between annual mass gained through snow accumulation and mass lost
due to melt runoff. In the relatively dry Canadian Arctic, surface mass balance
is determined primarily by the duration and intensity of the summer melt season
(Koerner, 2005), while glaciers in more temperate regions of Canada are also
influenced significantly by yearto-year variations in snowfall. Remote sensing
measurements generally cannot be used to directly estimate mass balance, with
the exception of very coarse resolution gravimetric measurements from the NASA
GRACE mission (approximately 450 km × 450 km), but remote sensing does
contribute valuable information on the melt/freeze state (Wang et al., 2005),
changes in ice thickness (Gray et al., 2016; Krabill et al., 2002; Berthier et
al., 2014), and glacier motion and iceberg calving (Strozzi et al., 2008, van
Wychen et al., 2016, Gray et al., 2001). For larger regions, models can be used
to estimate mass balance (Lenaerts et al., 2013; Gardner et al., 2011).
Long-term records of surface mass balance measurements from a small number of
Canadian glaciers are available through the World Glacier Monitoring Service.
Acquiring surface measurements for the determination of glacier mass balance is
logistically difficult, so only selected glaciers in the CAA and western
Cordillera are monitored.
5.4.1: Observed changes in glaciers
and ice caps
Climate
warming, combined with periods of reduced precipitation in Western Canada, has
contributed to total thinning of glaciers in the southern Cordillera by 30 to 50
m since the early 1980s (Zemp et al., 2015). By the mid-1980s, glaciers in
Garibaldi Provincial Park, southern British Columbia, had contracted in area by
208 km2 since the Little Ice Age maximum extent of 505 km2, with accelerated
shrinkage by another 52 km2 (or 7% of the Little Ice Age maximum) by 2005 (Koch
et al., 2009). Glacier extent at several sites in the central and southern
Canadian Rocky Mountains decreased by approximately 40% from 1919 to 2006
(Tennant et al., 2012). Glaciers of the Columbia Icefield, in the Canadian
Rocky Mountains, also experienced dramatic changes from 1919 to 2009, losing
22.5% of total area while retreating more than 1.1 km on average (Tennant and
Menounos, 2013). Aerial photography shows that all glaciers in British Columbia’s
Cariboo Mountains receded over the 1952–2005 period, with a loss of
approximately 11% in surface area (Beedle et al., 2015). In eastern Canada,
small alpine glaciers in the Torngat Mountains, Labrador shrunk by 27% between
1950 and 2005, with current thinning rates as high as 6 m per year across the
22 km2 of glaciers that remain in this area (Barrand, et al., 2017).
Glaciers and
ice fields covering approximately 10,000 km2 of the Yukon have decreased in
area by approximately 22% between 1957 and 2007, and thinned by 0.78 m water
equivalent (90% uncertainty range 0.44 to 1.12 m per year) contributing
1.12 mm (90% uncertainty range 0.63 to 1.61 mm) to global sea level over
this period (Barrand and Sharp, 2010). Mass balance of glaciers, measured at three
monitoring sites in Alaska (all within 300 km of the Kluane ice field, Yukon)
indicate a rapid change from positive to negative glacier mass balance in this
region beginning in the late 1980s (Wolken et al., 2017).
Long-term in
situ glacier monitoring indicates a trend of significant loss of mass for
glaciers and ice caps in the CAA beginning in the early 1990s (see Figure
5.13). Acceleration of glacier thinning in this region in the mid-2000s
coincided with increases in summer warming driven by the advection of warm air
masses to the Arctic from more southerly latitudes (Sharp et al., 2011;
Mortimer et al., 2016). Based on satellite measurements and surface mass-budget
models, total mass loss from glaciers and ice caps in the CAA has increased
more than two-fold, from 22 gigatonnes (Gt) per year between 1995 and 2000
(Abdalati et al., 2004), to 60 Gt per year (90% uncertainty range 52 to 66 Gt
per year) over the 2004–2009 period (Gardner et al., 2013), and 67 Gt per year
(90% uncertainty range 61 to 73 Gt per year) over the 2003–2010 period (Jacob
et al., 2012), with mass losses continuing to accelerate to 2015 (Harig and
Simons, 2016). According to the most recent assessments of regional glacier
change, glacier melting in the CAA has contributed 0.16 mm per year to
global sea-level rise since 1995, 23% of the contribution of the Greenland ice
sheet and 75% of the Antarctic Ice Sheet (Gardner et al., 2103; Shepard et al.,
2012; Sharp et al., 2016).
The Barnes
Ice Cap on Baffin Island, the last remnant of the Laurentide Ice Sheet that
covered most of Canada during the last glaciation, lost 17% of its mass from
1900 to 2010 (Gilbert et al., 2016). Approximately 10% of the total area of ice
in the CAA is composed of small, stagnant ice caps (the oldest are less than
3000 years old), located almost entirely under the regional equilibrium line
altitude, meaning they do not have an accumulation zone and experience net
thinning across their entire area in most years. These ice caps are shrinking
rapidly (Serreze et al., 2017) and fragmenting (Burgess, 2017), with many
expected to completely disappear within the next few decades. Of similar age to
the small ice caps are the ice shelves of northern Ellesmere Island, which are
composed of floating glacier ice and/or very thick old sea ice. These ice
shelves have decreased in area by about 90% since 1900 (with more than 50% of that
loss since 2003) and are expected to survive for only the next decade or two
(Mueller et al., 2017).
Like many
glaciers in the world, Canada’s glaciers are out of equilibrium with current
climatic conditions and will continue to lose mass for the foreseeable future.
Summer warming in the Arctic has driven extreme melting of ice caps and
glaciers over the past two decades, resulting in this region becoming the most
significant cryosphere contributor to global sea-level rise after the Greenland
and Antarctic ice sheets.
5.4.2: Projected changes in glaciers
and ice caps
Climate
model projections indicate that western Canada and the western United States
together (grouped together in many studies because of their similar mountainous
domain) could lose approximately 85% (90% uncertainty range 74% to 96%) of the
2006 volume of glaciers by the end of the century under a medium emission
scenario (RCP4.5). Under a high emission scenario (RCP8.5), this loss could
exceed 95% (Radic et al., 2014). Glaciers in the coastal ranges of western
Canada are predicted to lose 75% (90% uncertainty range 65% to 85%) of their
2005 ice area and 70% (90% uncertainty range 60% to 80%) of their volume by
2100 based on the mean of four emission scenarios (RCP2.6, 4.5, 6.0, 8.5)
(Clarke et al., 2015). Glaciers in the western Canadian interior are projected
to lose more than 90% of the 2005 volume under all scenarios except a low
emission scenario (RCP2.6) (Clarke et al., 2015). These changes, in combination
with the projected loss of alpine snow cover, will impact regional water
resources (Fyfe et al., 2017; see Chapter 6, Section 6.2). Glacier-fed rivers
may experience periods of increased discharge due to greater meltwater
contributions in a warmer climate, but this response is finite, and glacier
mass loss associated with warming is projected to result in reduced summer
streamflow by mid-century (Clarke et al., 2015). The rate and timing of this
transition will have important consequences for stream and river water quality
and temperature, and for the availability of water for human uses such as
hydro-electricity generation and agriculture.
Regional
land ice models project that glaciers and ice caps in the Canadian Arctic will
lose 18% of their total mass by 2100 (Radic et al., 2014; relative to a
baseline mass reference estimated by Radic and Hock, 2011) under a medium
emission scenario (RCP4.5), equivalent to 35 mm of global sea-level rise
(Lenaerts et al., 2013; Marzeion et al., 2012). This loss of land ice volume in
Arctic Canada by 2100 will contribute 41 mm of sea-level equivalent (90%
uncertainty range 26 to 56 mm) under RCP4.5, and 57 mm of sea-level equivalent
(90% uncertainty range 39 to 75 mm) under a high emission scenario (RCP8.5)
(Radic et al., 2014). Densification of high-elevation firm (partially compacted
granular snow that is the intermediate stage between snow and glacial ice) has
reduced or eliminated the internal storage capacity of the larger (more than
2000 km2) ice caps in this region, thus increasing their sensitivity to future
warming (Noël et al., 2018). Based on the trajectories of observed loss over
recent decades, many of the remaining small ice caps (less than 2000 km2) and
ice shelves in the Canadian Arctic are expected to disappear by 2100.
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