Smoke from Arctic wildfires may have caused Greenland's record thaw

Satellite images suggest soot particles settled over ice sheet making it absorb more heat during last year's extreme melting

The freak melt of the Greenland ice sheet last summer may have been forced by smoke from Arctic wildfires, new research suggests.

Satellite observations, due to be presented at the annual meeting of the American Geophysical Union on Friday, 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, due to be presented by the Ohio State University geographer Jason Box, go a step further, picking up images of smoke over Greenland at the time of last summer's extreme melt.

Greenland experienced its most dramatic melting since satellite records began last July, with virtually the entire ice sheet showing signs of a thaw over the course of four days. Box oversaw the Greenland portion of Noaa's annual report on the Arctic, which was released earlier this week and was in Greenland around the time of last summer's extraordinary melt.

two satellite images of the Greenland ice sheet
Measurements from three satellites showed that on 8 July, about 40% of the Greenland ice sheet had undergone thawing at or near the surface. By 12 July, this had increased to an estimated 97%. Photograph: REUTERS Photograph: REUTERS

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% decline in Greenland's reflectivity over the past decade. Under warming, ice crystals lose their jagged edges, becoming more rounded with reduced areas of reflectivity.

But the true extent of the loss could be much greater once the smoke from forest fires is factored in. "Soot is a very powerful absorber. Very small increases in soot content have big increases in solar absorption," Box said.

In its annual Arctic report, released this week this week, the premier scientific agency the National Oceanic and Atmospheric Administration, 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.

"We are tracking the fires from source to sink, the place where the smoke is depositing on the ice sheet. The scan can verify that the smoke is making it to its destination," Box said.

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 don't know. We have got to get up there and make those measurements."

Contributor

Suzanne Goldenberg, US environment correspondent

The GuardianTramp

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