Observations and Modelling of Glacier Mass Changes in Western Canada
The lower Athabasca Glacier, Jasper National Park. Photo: Kurt Morosson.
The retreat of mountain glaciers worldwide is a key indicator of modern climate change, with mass loss from glaciers contributing to sea level rise and to river flows during dry and warm parts of the year. In western Canada, maintenance of low flows by glacier meltwater is essential for maintaining biodiversity, hydro-power generation, agricultural irrigation, and water supply for major cities and small towns. The coming decades will see rapid and unprecedented changes to glaciers in western Canada.[1] However, current projections are unable to resolve with certainty how individual river basins will be impacted by the loss of glacier ice in their headwaters.
Figure 1. From Clarke et al. (2015): (a) Glacierized sub-regions in Western Canada used in the modelling study: Coast (1- St Elias, 2 - Northern Coast, 3 - Central Coast, 4 - Southern Coast, 5 - Vancouver Island; Interior (6 - Northern Interior, 7 - Southern Interior), and Rockies (8 - Northern Rockies, 9 - Central Rockies, 10 - Southern Rockies). Glacier extent from 2005 is indicated in white. Red dot in region 7 indicates the area in Caribou Mountain Range, for which the modelled glacier extent is shown for (b) year 2020 and (c) year 2100, in response to climate scenario from a global climate model.
Glaciers are one of Canada's important natural resources, serving as frozen reservoirs of water that supplement runoff in late spring, summer, and early autumn during periods of low river flow. The western provinces of British Columbia and Alberta together contain more than 15,000 mountain glaciers, totalling roughly 29,000 square-kilometres of glaciation (Figure 1). Estimates based on remote sensing indicate that glaciers in B.C. and Alberta have lost about eleven percent and twenty-five percent of their area, respectively, over the period of 1985-2005.[2] The thinning rate of these glaciers, however, has not been constant in recent times. The earliest estimate based on remote sensing methods reveals a thinning rate of about 78 (±19) centimetres a year between 1985-1999,[3] while the most recent study reports a slowing during 2000-2009, followed by an increase for 2009-2018.[4] The largest increase (by twenty percent) in the rate of ice thinning relative to 1985-1999 is reported for the Coast Mountains of B.C. (sub-regions 3-5 in Figure 1). This volume is comparable to the loss of one large Himalayan glacier annually! It is still unknown what has driven the variable rate in glacier mass loss over the last four decades: whether it is the natural climate variability known to affect glacier mass balance along the west coast of North America, stochastic variability, or whether these recent changes are related to anthropogenic climate change.[5]
Eyebrow Peak,Purcell Mountains, 2015. Photo: Zac Robinson.
The Shackleton Glacier, Rocky Mountains, 2010. Photo: Zac Robinson.
Over the last decade, glacier models of different complexity have simulated future mass changes on global and regional scales in response to climate scenarios from Global Climate Models (GCMs).[6] But despite differences in their structure and calibration, all the models agree that glaciers in western Canada and United States (without Alaska) will lose more than fifty percent of their current mass by the end of the century (Figure 2). A model, developed by coupling physics-based ice dynamics with a surface mass balance model, has projected the fate of glaciers in western Canada in response to the climate scenarios from an ensemble of Global Change Models.[7] The results indicate that, by 2100, the volume of glacier ice will shrink by seventy percent (± ten percent) relative to 2005. According to these simulations, few glaciers will remain in the interior of western Canada and the Rockies (sub-regions 6-10 in Figure 1), but maritime glaciers, in particular those in northwestern B.C. (sub-regions 1-2 in Figure 1), will survive, but in a diminished state. The model also projects the maximum rate of ice volume loss, corresponding to peak contribution of meltwater to streams and rivers, to occur around 2020-2040. The resulting decrease in late summer streamflow, as glaciers keep diminishing from the watersheds, will have large implications for aquatic ecosystems, agriculture, forestry, alpine tourism, and water quality.
Figure 2. From Hock et al. (2015): Projected time series of glacier mass 2015–2100 for Western Canada and United Stated (without Alaska) based on six glacier models, each one using RCP8.5 emission scenario (the most extreme scenario in terms of future emissions of greenhouse gases) and an ensemble of Global Climate Models (GCMs). Glacier mass is normalized to mass in 2015. Thick lines show multi-GCM means for each glacier model (each glacier model has different color) and thin lines mark the results from individual GCMs.
Figure 3. Automated weather station with glacio-meteorological sensors that measure all components of surface energy balance, installed at Nordic glacier in the Rockies in summer 2014. Photo: Noel Fitzpatrick.
Despite the recent substantial progress in large-scale measurements and modelling of glacier mass changes, large uncertainties remain in the projections of glacier mass loss. The global climate signal needs to be translated into a local one (a process known as “downscaling”) in order to resolve processes that drive the mass gain (e.g. snowfall) and mass loss (e.g. surface melting) at a scale of individual glaciers in the region. All current models rely on relatively simple statistical downscaling methods that have limited applicability since they require observations from weather stations installed at glacier surfaces. Fewer than one percent of glaciers worldwide, including only a handful of glaciers in western Canada, have these necessary measurements (an example of a weather station installed at a glacier surface is shown in Figure 3). The lack of meteorological observations at glaciers also presents an impediment for a development of physics-based models of glacier melt to be successfully applied on regional and global scales. These models attempt to account for all components of surface energy balance (e.g. incoming solar radiation, longwave radiation, and turbulent heat fluxes), which contribute to the energy available for melt. The poorly constrained parameters in empirical models based on observational data can lead to large uncertainties in the projections of glacier mass loss and their contribution to streamflow, especially at local scales. Resolving the uncertainties and providing more accurate estimates about the future of glacier-fed water resources will be relevant to local policymakers and user communities, and improvements in all these areas of modelling and observations are needed.
Author Bio
Dr. Valentina Radic is an Associate Professor in the Department of Earth, Ocean and Atmospheric Sciences at the University of British Columbia. Dr. Radic completed a MSc in 2004 in geophysics at University of Zagreb, Croatia, and a PhD in 2008 in geophysics/glaciology at University of Alaska Fairbanks. She did four years of postdoctoral work at the University of British Columbia prior to joining the faculty in 2012.
References
[1]Clarke, G. K. C., Jarosch, A. H., Anslow, F. S., Radić, V., & Menounos, B. Projected deglaciation of western Canada in the twenty-first century. Nature Geoscience 8 (5), 372–377 (2015).
[2]Bolch, T., Menounos, B., & Wheate, R. Landsat-based inventory of glaciers in western Canada, 1985–2005. Remote Sensing of Environment 114 (1), 127–137 (2010).
[3]Schiefer, E., Menounos, B., & Wheate, R. Recent volume loss of British Columbian glaciers, Canada. Geophysical Research Letters 34, L16503 (2007).
[4]Menounos, B. et al. Heterogeneous changes in western North American glaciers linked to decadal variability in zonal wind strength. Geophysical Research Letters 46, 200–209 (2019).
[5]Ibid.
[6]Hock, R. et al. GlacierMIP - A model intercomparison of global-scale glacier mass-balance models and projections. Journal of Glaciology 65(251), 453-467 (2019).
[7]Clarke, G. K. C., Jarosch, A. H., Anslow, F. S., Radić, V., & Menounos, B. Projected deglaciation of western Canada in the twenty-first century. Nature Geoscience 8 (5), 372–377 (2015).