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Arctic Wildfires Speed Melting of Greenland Ice: Study

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SAN FRANCISCO — Smoke from Arctic wildfires may have contributed to the melting of the Greenland ice sheet during the 2012 melt season, according to new research to be presented at a scientific conference in San Francisco on Friday. The research, led by Jason Box of Ohio State University, provides the first satellite-based evidence that smoke from Arctic wildfires is reaching the Greenland ice sheet, where it acts as an amplifier of the warming already occurring from manmade emissions of greenhouse gases, such as carbon dioxide.

Aerial photo of the Greenland ice sheet surface from mid-August, 2005. The dark areas are concentrations of light absorbing impurities. This example the impurities are some combination of dust, soot, and microbial activity.
Click to enlarge the image.
Credit: Jason Box.

Wildfire smoke contains dark-colored soot and other particles which, when deposited onto the Greenland ice sheet, cause the ice and snow surfaces to darken and absorb more incoming solar radiation, and therefore melt more readily. Box said that wildfire smoke may be responsible for a dramatic expansion in the portion of Greenland that experiences melting during the summer season.

During July of this year, melting was observed even at the highest elevations in Greenland, with the melt extent reaching a record 97 percent of the ice sheet on a single day. This is nearly four times greater than the typical 25 percent average melt extent observed during the 1981 to 2010 period, according to a separate Arctic report released on Wednesday.

As was first reported by Climate Central in June, Box observed a record low in the reflectivity of the Greenland ice sheet during the 2012 melt season, which he attributed partially to the influence of dark-colored particles on the bright, highly reflective snow and ice cover. He and his colleagues have found that the reflectivity of the Greenland ice sheet has declined by 6 percent in the last decade, which is helping to cause melting even in the coldest areas of the island. However, exactly how much of that decline is attributable to soot from wildfires is not yet clear.

Profile of the atmosphere above Greenland's ice sheet, showing areas of what researchers say is wildfire smoke. 
Click to enlarge the image.
Credit: Ohio State/NASA CALIPSO satellite.

"Soot is an extremely powerful light absorber," Box said in a press release. "It settles over the ice and captures the sun's heat. That's why increasing tundra wildfires have the potential to accelerate the melting in Greenland."

A comprehensive annual report on the state of the Arctic, which was released on Wednesday, found that global warming is causing an increase in Arctic wildfires, as vegetation cover increases and thunderstorms, which are a key ignition source for wildfires, become more numerous during the Arctic summer. The report found that conditions have been particularly favorable for Alaskan wildfires during the past several years.

The high reflectivity of snow is one factor that has kept Greenland so cold by bouncing incoming heat from the sun back out toward space. But with several factors combining to increase temperatures in Greenland and reduce the reflectivity of the snow and ice cover, the ice sheet is becoming less efficient at reflecting that heat energy, and as a consequence melt seasons are becoming more severe.

Freshly fallen snow reflects up to 84 percent of incoming sunlight, but during the warm season the reflectivity declines as the ice grains within the snowpack change shape and size. In addition, once snow cover melts completely it often reveals underlying ice that has been darkened by dust and other particles, whose surface absorbs more solar energy, promoting heating.

Greenland ice melt extent trends, showing the extensive melt in 2012.
Credit: 2012 Arctic Report Card.

Greenland is the world's largest island, and it holds 680,000 cubic miles of ice. If all of this ice were to melt — which, luckily won't happen anytime soon — the oceans would rise by more than 20 feet.

Drew Shindell, a NASA climate researcher who was not involved in this research, said there are still many open questions about how wildfires are contributing to Greenland melt. "The link between fires, black carbon [soot] and melting seems quite reasonable, but I too would want to see some more measurements to know if the contribution from this was important or not," Shindell said in an email message. "It'd be good to see how variations in fires from year-to-year correspond with variations in melting to reinforce their claim."

To find evidence of soot deposition from these fires, Box and his colleagues, including Thomas Painter of NASA's Jet Propulsion Laboratory and graduate student McKenzie Skiles of the University of California, Los Angeles, first used thermal images from NASA's Moderate Resolution Imaging Spectroradiometer (MODIS) to spot large Arctic wildfires. They then calculated possible smoke particle trajectories, which showed that smoke could be reaching Greenland, particularly from fires in Alaska and parts of Canada. They then used those trajectories to scrutinize thermal imagery from another NASA satellite to pinpoint sooty aerosols over Greenland.

In order to get an accurate measure of the extent of the soot particle contribution to the Greenland melt, it's also neccesary to obtain ground-based evidence. To accomplish this task, Box is planning an expedition to the ice sheet in 2013, called the Dark Snow Project. He said it would be a funded through crowdsourcing, making it the first such scientific ice expedition of its kind.

Box has been an outspoken advocate of reducing greenhouse gas emissions, going as far as taking part in protests against the Keystone XL oil pipeline at the White House in 2011. 

Related Content:
Warming Driving Arctic Into New, Volatile State
Greenland Ice Sheet Nearing Critical 'Tipping Point'
The Story Behind Record Ice Loss in Greenland

Comments

By Jack Burton (Two Harbors, MN, 55616)
on December 7th, 2012

This is another of the unforeseen positive feed backs that is making the linear models unreliable. We all know that predictions for Greenland melting were all out into the 2050’s and nothing really serious till 2100. But now observations are destroying these model based predictions.
The list of Feed Backs that are beginning to make themselves felt is long and growing. The most simple of them, and yet one of the strongest is the arctic sea ice melt of 2012. The open water exposed to long days of sunlight is allowing massive uptake of heat from solar input, this is a huge positive feedback in place of reflective white ice. Even the thinnest of ice cover gives the reflection effect. Once ice is replaced with open water, then a powerful force warms the water and makes ice formation later and thinner, next spring there is less thickness and quicker melting. Then the effect is magnified again till soon there is no ice at all.
The melting permafrost is kicking in CO2 and methane, driving more melting, driving more CO2 and Methane.

I am no scientist, I can only observe the data published and reported and make an educated guess as to what is going on. My guess is that we have entered the Feed Back era, when they drive the warming by orders of magnitude above what linear models had predicted. All the evidence is pointing that way.
Extreme weather is also in run away mode. The nature of “Sandy” was mind blowing, it’s size and course unprecedented in a year when arctic melting drove arctic air temps to new highs and sending the jet stream into wild gyrations. Greenland in the south had some record warm temperatures in early summer.
I say the models have been destroyed by observation. I say this is due to the beginning of massive feed back effects.
Bad news all around. Though this will NOT slow down the deniers and their Fossil Fuel Company Public Relations professional deniers and those who believe the PR.

Reply to this comment

By John Paily
on December 12th, 2012

The increased climate catastrophes by accelerated climate change and human misery and restlessness cannot be alleviated unless we awaken Heat or energy cycle of nature and how earth works to sustain it. Increasing Heat means unwinding and more fire bound destructions and fragility of earth. Earth reaction to oppose the heat manifests as winding. This means more of flash floods, flash snows, more earthquakes and eventually huge volcanic eruptions – Yellowstone which is due, can erupt any time. History and science tells that volcanic dust cools the environment. Earth will not stand to debate with rich nations and business people. We are heading for a disaster. Only thing that can save humanity is Knowledge and awakening to Truth – we need awaken to the Principle and Design on which Earth functions to maintain certain ratio of energy to matter and thus the heat. We need to develop energy management of earth and develop New Green Technologies that are nature compatible and releases less heat. This is a life time research. Some organizations needs to look into it and bring it to worlds notice and awaken it to save humanity from greater misery- Take it as an SOS    
http://www.scribd.com/doc/114273537/Climate-Change-and-Its-Relation-to-Energy

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