[font face=Serif]Public Release: 30-Oct-2015
[font size=5]Arctic snow not darkening due to soot, dust, Dartmouth-led study finds[/font]
Dartmouth College

[font size=3]HANOVER, N.H. - For millennia, Greenland's ice sheet reflected sunlight back into space, but satellite measurements in recent years suggest the bright surface is darkening, causing solar heat to be absorbed and surface melting to accelerate. Some studies suggest this "dirty ice" or "dark snow" is caused by fallout from fossil fuel pollution and forest fires.

But a new Dartmouth-led study shows that degrading satellite sensors, not soot or dust, are responsible for the apparent decline in reflectivity of inland ice across northern Greenland. The study's results suggest the ice sheet hasn't lost as much reflectivity as previously thought, and that black carbon and dust concentrations haven't increased significantly and are thus not responsible for darkening on the upper ice sheet.

The findings, which contradict anecdotal observations and earlier scientific studies, appear in the journal Geophysical Research Letters. A PDF of the study is available on request.

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Instead, the findings suggest the apparent decline in the dry snow zone's reflectivity is being caused by uncorrected degradation of sensors in NASA's aging MODIS satellites and that the declining trend will likely disappear when new measurements are reprocessed. MODIS (or Moderate Resolution Imaging Spectroradiometer) is the key instrument aboard NASA's Terra and Aqua satellites, which provide images of the Earth's surface and cloud cover every two days. MODIS tracks features of the land, oceans and atmosphere that can help develop models that predict global changes. The Terra mission, launched in December 1999, and the Aqua mission, launched in 2002, are designed to collect data for 15 years to differentiate short- and long-term trends and regional and global phenomena.

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