Wildfires Melt Glaciers From a Distance

Scientists have begun to trace a link between climate change, an increased number of wildfires and glacier melting.  Particles emitted by wildfires and then deposited on glaciers are thought to darken the ice’s surface, and may lead to more rapid melting.

Natalie Kehrwald, a geologist from the United States Geological Survey (USGS), is currently studying the levels of wildfire particles deposited on the Juneau Icefield in Alaska. Kehrwald and her fellow USGS geologist, Shad O’Neel,  who is tracking the retreat of glaciers in the Juneau Icefield, are working together to document the contributions of wildfires to glacier melting.

Collecting ice cores on the Juneau Icefield (Source: Natalie Kehrwald).

“In the past two to three years there have been huge wildfires [in Alaska]… I am trying to see if there are aerosols being deposited on the Juneau ice field and if they are accelerating the melting,”  said Kehrwald in an interview with GlacierHub.

According to multiple sources, including the University of Alaska Fairbanks and the non-profit research and news organization Climate Central, rising Arctic temperatures are creating longer and more severe wildfire seasons, with larger and more frequent fires.  Kehrwald proposes that an increase in wildfires has led to a greater volume of aerosols, a mixture of carbon and other particles, deposited onto glaciers.  There may be a minor feedback as well. Since glaciers act as large mirrors and keep the planet cooler by reflecting solar energy back into space, the loss of glaciers could also accelerate the rise in temperaturse.

In early August, Kehrwald and O’Neel led a team of student researchers from the Juneau Icefield Training Program into the field, where they gathered ice cores.  They will later analyze these cores for wildfire indicators in a lab.  

Natalie Kehrwald’s team of Juneau Icefield Research Program students (Source: Natalie Kehrwald).

“We take samples from the highest, flattest parts of the glacier in specific locations that are impacted by air masses.  We drill down 7-9 meters, which date back about two to three years,” said Kehrwald, summarizing their trip.

The carbon deposits from wildfires can be grouped into a larger category called black carbon, which have been linked to rapid glacier melting.  Black carbon refers to carbon released from both biomass burning and fossil fuel emissions.  In order to determine whether the carbon on the Juneau Icefield is from wildfires, Kehrwald will look for a specific molecular marker in the ice.  

“It is a sugar called levoglucosan and it is only produced if you burn cellulose at a temperature of about 250 degrees Celsius,” said Kehrwald.  “So if you see high concentrations of that molecule you know the origin is biomass burning, which is generally wildfires but could be a big compilation of household fires.”

A team of Alaskan  firefighters marches down to meet the flames (Source: BLM Alaska Fire Service/Facebook).

Although the Alaskan wildfires occur predominantly in the boreal forest located in a drier region far north of the Juneau Icefield, smoke from wildfires have been known to travel great distances.  The phenomena of darkening glaciers due to particles from wildfires was well documented last year when large wildfires in British Columbia deposited particles on glaciers across the North American Arctic and as far as Greenland.

According to the University of Alaska Fairbanks, three of the top ten largest Alaskan wildfires since 1940 occurred in the last decade.  In 2015, Alaskan wildfires burned over 5 million acres of land.  Alaska’s burnt acreage represented five-sixths of the national total land consumed by wildfires in that year, according to The Washington Post.  The acreage of wildfire burned land in 2015 is second only to the approximately 6.5 million acres burned in 2004.

A 2015 report, The Age of Alaskan Wildfires, produced by non-profit group Climate Central stated that large Arctic wildfires are no longer rare.  

Satellite image showing Alaskan wildfires on June 25, 2015. Actively burning areas are outlined in red. NASA image courtesy Jeff Schmaltz, MODIS Rapid Response Team. Caption: NASA/Goddard, Lynn Jenner (Source: nasa.gov).

“We found the number and size of areas burnt by large wildfires [in Alaska] is on the rise since the 1950s,”  stated Todd Sanford, climate scientist at Climate Central.  “Looking at the length of the fire season in Alaska we found, like in the western US, the length of the season is increasing each year…. Wildfire seasons are over a month longer than they were in the 1950s.”

Additional research will further expand understanding of how much wildfires may affect glacier melting.

“In regards to the glaciers in southeast Alaska,” Kehrwald told GlacierHub “we don’t know if it [the reason for the rapid melting of the Juneau Icefield] is temperature only… or if it’s also due to imputes from outside components such as wildfires.”
Kehrwald and O’Neel plan to test their ice core samples in the lab and by later this year have a clearer view of how a greater number of wildfires due to rising temperatures can contribute to glacier melting.

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