In recent years, satellite photos of Greenland's ice sheet have shown what appears to be a darkening of the ice's surface. A number of scientists have suggested that this could be due to settled soot particles from fossil fuel production and/or forest fires, and that their presence could result in accelerated melting of the ice. Now, however, researchers from Dartmouth College believe that the ice may still still be relatively clean, and that its darkness in the photos could just be due to faulty sensors on the satellites.
Ordinarily, untainted ice sheets reflect much of the sunlight that hits them back up into the sky, limiting how much solar heat is absorbed by the ice. With the Greenland ice sheet, the concern has been that dark carbon particles in the ice are allowing it to absorb more heat, speeding up the process at which the ice will ultimately melt away for good.
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Led by Prof. Chris Polashenski, Dartmouth scientists analyzed dozens of snow samples taken from the ice sheet between 2012 and 2014, and compared them to samples taken over the prior 60 years. They reportedly found no significant difference in the amount of black carbon particles or mineral dust in the samples. Additionally, they ruled out algae as the culprit.
Instead, the researchers are suggesting that uncorrected degradation of sensors in NASA's MODIS (Moderate Resolution Imaging Spectroradiometer) satellites could be making the ice in the photos look darker than it actually is. Furthermore, they believe that the anomaly will likely disappear when the satellite data is reprocessed to compensate for the degradation.
They add, however, that their findings only apply to ice in the sheet's higher elevations. It still is possible that pollution or algae growth in the lower elevations could be diminishing the reflectivity of the ice.
A paper on the research was recently published in the journal Geophysical Research Letters.
Source: Dartmouth College