Climate Change Canada

 

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.