An anonymous reader writes with word of a a new study of the Greenland ice sheet
led by Dartmouth adjunct assistant professor Chris Polashenski, which maintains that the darkening sensed there by satellites is not caused by dust and soot deposited by forest fires and industry, but rather by the slow degradation of the sensors on the satellites themselves.
[Polashenski] and his colleagues analyzed dozens of snow-pit samples from the 2012-2014 snowfalls across northern Greenland and compared them with samples from earlier years. The results showed no significant change in the quantity of black carbon deposited for the past 60 years or the quantity and mineralogical makeup of dust compared to the last 12,000 years, meaning that deposition of these light absorbing impurities is not a primary cause of reflectivity reduction or surface melting in the dry snow zone. Algae growth, which darkens ice, also was ruled out as a factor. 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.