Soot, smoke link to extreme ice melt
THE FREAK melt of the Greenland ice sheet this year may have been forced by smoke from Arctic wildfires, new research suggests.
Satellite observations presented at the annual meeting of the American Geophysical Union yesterday, for the first time tracks smoke and soot particles from tundra wildfires over to Greenland.
Scientists have long known that soot blackens snow and ice, reducing its powers of reflectivity and making it more likely to melt under the sun.
But the satellite records, presented by the Ohio State University geographer Jason Box, go a step further, picking up images of smoke over Greenland at the time of this year’s extreme melt.
In July, Greenland experienced its most dramatic melting since satellite records began, with virtually the entire ice sheet showing signs of a thaw over the course of four days. Box oversaw the Greenland portion of the National Oceanic and Atmospheric Administration (Noaa) annual report on the Arctic, which was released last week and was in Greenland around the time of the extraordinary melt. It said the thaw was due to the warming atmosphere caused by climate change, as well as local weather conditions over Greenland including clear bright skies and a lack of fresh snow cover. But Box said scientists are now beginning to identify another important cause for melting: smoke and soot particles, darkening the surface of the Greenland ice sheet.
Earlier research found a 7 per cent decline in Greenland’s reflectivity over the past decade. ‘‘Soot is a very powerful absorber. Very small increases in soot content have big increases in solar absorption,’’ Box said.
In its Arctic report, Noaa warned greener and warmer conditions due to climate change were making the tundra more fire-prone.
When soot from those fires settles over the ice, it captures the sun’s heat. ‘‘That’s why increasing tundra wildfires have the potential to accelerate the melting in Greenland,’’ Box said.
Box and his team used Nasa satellites to spot large fires which burned for several days in Labrador last summer, and computer models to anticipate smoke trajectories. They then used satellite imaging to detect sooty aerosols, or smoke clouds, directly over Greenland.
He said he planned to return to Greenland in the early summer of 2013 to take samples from the ice sheet in a crowd- sourced expedition, the Dark Snow project.
‘‘We saw complete surface melting of the ice sheet for the first time in observation. Would that have happened without the wildfire soot of 2012?’’ Box said. ‘‘We have got to get up there and make those measurements.’’