Jeff Fritzsche, Environment Accounts and Statistics Division
Glaciers throughout the world are dynamic, constantly losing and gaining snow and ice. A glacier’s mass can increase through the accumulation of snow and other types of frozen precipitation. On the other hand, a glacier can lose mass (a process known as ablation) through processes such as melting, evaporation and calving.
Glacier mass balance measures the net results of accumulation and ablation and is expressed in millimetres of water equivalence. 1 The difference between accumulation and ablation for a glacier over a given year is the net (mass) balance. The charts in this article feature cumulative mass balance, which adds together sequential annual measurements over a number of years. The cumulative mass balance indicates magnitude, direction, trend and the presence of acceleration with regard to the change of mass over time. In the case of the six glaciers presented in this article, the cumulative mass balance estimate is calculated for each glacier through the length of the glacier’s time series. This allows scientists to assess if the glaciers are in equilibrium, growing, or shrinking over the time period in question and whether that rate of change is accelerating.
This article is the first of a new series in EnviroStats to present data related to Canada’s climate and the impacts of climate change. The focus of these articles will be short statistical analyses of climate related data, such as sea ice extent and glacier mass balance.
This series is the product of ongoing collaboration among Statistics Canada, Environment Canada and Natural Resources Canada to make data related to Canada’s climate easily and regularly accessible.
This collaboration will also ensure that the data featured in these EnviroStats articles will be available through the Statistics Canada website, both through free CANSIM data tables and through new articles re-examining trends every few years.
For readers who are interested in obtaining further information related to glaciers and the effect of climate, please visit http://sst-ess.rncan-nrcan.gc.ca/ercc-rrcc/proj3/theme1/index_e.php.
The mass balance of glaciers is very sensitive to fluctuations in climate 2 resulting in direct and immediate responses to these fluctuations. 3 For this reason, this measure is considered by the World Meteorological Organization-Global Climate Observing System as an Essential Climate Variable 4 and is thought to provide one of the clearest signals found in nature to monitor ongoing trends in climate. 5
This article focuses on data for six glaciers found in two regions, the Western Cordillera (Map 1) and the High Arctic (Map 2). These data are part of Canada’s contribution to the World Glacier Monitoring Service, 6 which reports on a network of glaciers throughout the world.
Charts 1 and 2 show the cumulative mass balance for the monitored glaciers in each region. In these charts the mass gain or loss of glaciers is tallied up over time. An upward sloping line means the glaciers are gaining mass; a downward one indicates mass loss. If the line is getting steeper, the loss or gain is accelerating. Different types of time-series trend analysis were performed on the data for each glacier. All methods revealed that each glacier showed a statistically significant loss of mass over the time period analysed.
The glacier mass balance time series includes six glaciers (Maps 1 and 2), three located in the mountains of British Columbia and Alberta of the Western Cordillera and three located in the High Arctic. These six glaciers form Canada’s contribution to the Global Terrestrial/Climate Observing System and World Glacier Monitoring Service. 7
The glacier data used in this article are derived from Natural Resources Canada’s Earth Science Sector’s Climate Change Geoscience Program, which supports Canada’s national glacier-climate observing system. Research and monitoring of Canada’s glaciers is conducted in partnership with several government departments and universities.
Western Cordillera glaciers:
High Arctic glaciers:
The data series for each glacier varies in duration, from a minimum of 30 years to a maximum of 48 years. A number of analytical techniques were applied to the data, in both raw and smoothed form, to determine if statistically significant trends existed. These techniques ranged from ordinary least squares analysis to a non-parametric analytical approach using Sen’s method. 8 Linear regression was run on the raw and on the smoothed data, while Sen’s method was applied to the raw data only. Various time series models were fitted to the data to identify the one that provided the best fit. All six techniques showed that the cumulative mass balance time series for all six glacier sites showed statistically significant decreases. The linear regression method provided the most suitable fit to the data and these results are depicted in this study. 9
Ideally, trends in glacier mass balance should be analyzed using as long a time period as possible. However, the cumulative mass balance time series featured in this article are of short duration relative to the lifespan of a glacier. Glaciologists use other sources of information in order to put these observations into the long-term context, including, evidence left behind by the retreating glaciers hundreds and thousands of years ago as well as new mapping and remote sensing data.
Although the mass of all six glaciers declined, there were regional differences, with the glaciers located in the High Arctic showing a less pronounced loss of mass than those in the Western Cordillera. These regional differences can be attributed to several factors, such as the size of the individual glaciers, as smaller glaciers will lose mass at an accelerated rate given similar weather and topographic conditions in comparison to their larger counterparts. The High Arctic features both larger individual glaciers as well as a greater extent of glacier cover (approximately 150,000 km2) than the Western Cordillera Mountains (approximately 50,000 km2) which extend into British Columbia, Alberta and the Yukon. 10
The three glaciers of the Western Cordillera all experienced a loss of mass (Chart 1). The Helm and Place Glaciers, both located in the southern Coast Mountains of British Columbia, experienced the most significant decrease of the three glaciers in this area. The Peyto Glacier, located in Banff National Park, Alberta, lost more mass than the glaciers located in the High Arctic, but less than Helm and Place glaciers. The Peyto Glacier experienced an early period of stable mass, but began showing a downward trend in the late 1970s that continued to the end of the period.
All three High Arctic glaciers are located in Nunavut (Map 2). Like the three glaciers located in the Western Cordillera, the three glaciers located in this area also showed a loss of mass (Chart 2). Their rates of loss, however, were lower than for the glaciers in the Western Cordillera. The Devon Ice Cap showed a gradual downward trend throughout the entire time period, but with a more pronounced loss of mass from the mid-1990s to 2007. The Meighen Ice Cap, on Meighen Island, shrank at a faster rate than the Devon Ice Cap. It decreased more rapidly in the first half of the 1960s, and then experienced a slower rate of decline. The White Glacier on Axel Heiberg Island, also showed a significant downward trend, and like the Devon Ice Cap, has shown a more pronounced loss of mass from the mid-1990s to 2007.
Glaciologists use a variety of information in order to put these relatively shorter observations into context. Analysis of evidence left behind by the retreating glaciers hundreds and thousands of years ago, and new mapping and remote sensing data, has helped glaciologists place these mass balance data in a longer term context. Analysis by glaciologists at Natural Resources Canada suggests the rate and amount of mass loss for sites in the Western Cordillera have occurred at an unprecedented pace towards a state not in evidence for several millennia. 11
The six glaciers studied for this article experienced statistically significant reductions in their mass over the length of the data series. The major difference between the two regional groups of glaciers was the rate of mass loss, with the glaciers in the Western Cordillera losing mass at a faster rate than those in the High Arctic. These findings are consistent with international research, which shows that worldwide and rapid glacier shrinkage has been taking place over the past century. 12