Trends, Patterns and Influences of Glacier Albedo, Western North America.

Abstract:

Western North American glaciers experienced strong mass loss over the last two decades, but this loss was not spatially uniform. Mass loss is hypothesized to be driven by an increase in surface air temperature and changes in regional precipitation. The degree to which these changes are also influenced by changes in surface albedo remains uncertain, however. We utilize the MODIS daily snow albedo (MOD10A1) product to assess changes in surface albedo for the glaciated regions within Randolph Glacier Inventory zones 1 and 2, divided into 17 regions, over the last two decades. These glaciated regions extend from Cascade and Rocky Mountains of the US to the north slope of Alaska. We compare trends in glacier albedo for each of the 17 regions against ERA5 Land 2 metre air temperature and MODIS monthly aerosol (MOD08_M3 & MYD08_M3) to determine the relative influence on the albedo time series. Over the last 20 years, we observe significant decreases in albedo for glaciers in the coast, interior and Rockies regions of Canada. Our criterion for regionally-significant decreases in albedo was that 25% of albedo grid cells within a given region needed to display significant decreases. Of these 17 regions, we observe a decrease in albedo between 4-81%. Interior and Rocky Mountain regions of western Canada experienced the strongest decreases in albedo that averaged 0.3-0.5% yr^-1. Results from multiple linear regression analysis of albedo and ERA5 temperature plus MODIS aerosol optical depth showed that most regions covary with temperature, but albedo in the North Coast, Interior and Rocky Mountains also covaries with aerosol loading. Times of elevated aerosols coincide with years of large forest fire activity, suggesting that forest fire aerosol deposition can influence regional patterns of glacier albedo.