Dust Darkens Greenland Ice Sheet Speeding Melt due to a change in Albedo
08.06.2014
A new paper in Nature Geoscience says dust on the surface of the Greenland ice sheet is absorbing solar warmth and accelerating melting. It suggests that the dust comes from other Arctic areas losing snow cover earlier due to climate change.
Click to enlarge. Observed broadband diuse albedo above 2,000 m a.s.l. Diffuse broadband albedo derived from MODIS MCD43A3 products for the May–July period from 2003 to 2013. The values are averaged over the GrIS above 2,000 m elevation. Only data with local solar elevation larger than 25o and labelled as high quality are used. The 2003–2008 mean and the standard deviation are indicated in grey shades. Individual 2003 to 2008 albedo series are shown as grey dashed lines. Courtesy: authors and Nature Geoscience.
Click to enlarge. Melting snow containing light absorbing impurities.
Here is the Nature press release relating to this story.
The springtime darkening of the Greenland ice sheet since 2009 may be attributable to an increase in the amount of impurities—such as dust—in snow, according to a study published online in Nature Geoscience. Impurities, which increase the solar energy absorbed by snow, can lead to enhanced melting and thus contribute to the loss of Greenland’s ice.
Marie Dumont and colleagues analysed satellite observations to show that the observed darkening of Greenland’s ice in springtime months is consistent with a widespread increase in the amount of light-absorbing impurities. They propose that dust originating from other Arctic areas, which are losing their snow cover earlier in the spring as the climate warms, may be the source of the impurities.
Numerical snow models suggest that the darkening of springtime snow due to light-absorbing impurities has led to significant mass loss of the Greenland ice sheet in recent years.
Abstract
The surface energy balance and mass balance of the Greenland Ice Sheet depends on the albedo of snow, which governs the amount of solar energy that is absorbed. The observed decline of Greenland’s albedo over the past decade has been attributed to an enhanced growth of snow grains as a result of atmospheric warming. Satellite observations show that, since 2009, albedo values even in springtime at high elevations have been lower than the 2003–2008 average. Here we show, using a numerical snow model, that the decrease in albedo cannot be attributed solely to grain growth enhancement. Instead, our analysis of remote sensing data indicates that the springtime darkening since 2009 stems from a widespread increase in the amount of light-absorbing impurities in snow, as well as in the atmosphere. We suggest that the transport of dust from snow-free areas in the Arctic that are experiencing earlier melting of seasonal snow cover as the climate warms may be a contributing source of impurities. In our snow model simulations, a decrease in the albedo of fresh snow by 0.01 leads to a surface mass loss of 27 Gt yr, which could induce an acceleration of Greenland’s mass loss twice as large as over the past two decades. Future trends in light-absorbing impurities should therefore be considered in projections of Greenland mass loss.
2 Degrees Centigrade 