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11 May 2017

Warming Alaskan Tundra Causing Surge in Carbon Emissions during Early Winter

Contained within the icy tundra of Alaska is a massive deposit of carbon dioxide; the result of un-decayed organic matter from dead vegetation which has accumulated in the frozen soil over thousands of years. It is estimated that soils in the region above 60° North latitude hold enough CO2 to double the current atmospheric concentration of the potentially-damaging greenhouse gas.

During each Arctic summer, as the upper layers of soil begin to thaw, microbes decompose the aforementioned organic matter and produce carbon dioxide in vast quantities. The return of cold temperatures in October re-cools the soil until it ultimately refreezes, slowing the release of such gases. However, a new research paper led by Roisin Commane, an atmospheric researcher at Harvard University in Cambridge, Massachusetts, has found that he amount of carbon dioxide emitted from northern tundra areas between October and December each year has increased by 70% since 1975. They attribute this increase to warmer temperatures during the onset of the Arctic winter, which delays the cooling and refreezing of the carbon-rich soil and allows more CO2 to be released into the atmosphere. They further speculate that the increase in CO2 released to the atmosphere will accelerate climate warming, which, in turn, could lead to the release of even more carbon dioxide from these soils.

Img: Bering Land Bridge National Preserve
The study involved the analysis of three years’ worth of aircraft observations from NASA’s Carbon in Arctic Reservoirs Vulnerability Experiment (CARVE) airborne mission, from which the team were able to estimate the spatial and seasonal distribution of Alaska’s CO2 emissions. They combined this data with that gleaned from the study of NOAA’s 41-year record of CO2 measured from ground towers in Utqiagvik (formerly known as Barrow), Alaska. This combination provided them with unprecedented spatial data and long-term measurements unavailable elsewhere in the Arctic.

Study lead Roisin Commane said of the team’s results, “In the past, refreezing of soils may have taken a month or so, but with warmer temperatures in recent years, there are locations in Alaska where tundra soils now take more than three months to freeze completely. We are seeing emissions of carbon dioxide from soils continue all the way through this early winter period."

Co-author Colm Sweeney, of the Cooperative Institute for Research in Environmental Sciences in Boulder, Colorado, added, “Data from Barrow (Utqiagvik) show steady increases of both atmospheric carbon dioxide and temperature in late fall and early winter. This new research demonstrates the critical importance of these long-term monitoring sites in verifying the subtle feedbacks, such as increases in carbon dioxide, which may amplify the unprecedented warming we are seeing throughout the Arctic.”

The CARVE airborne mission, from which much of the data was gained, used an instrumented NASA aircraft to measure atmospheric CO2 and other greenhouse gases over Alaska from April to November in 2012, 2013 and 2014. By combining these measurements with other ground and satellite data, the scientists were able to generate a detailed picture of carbon emissions at the regional level.

“One of CARVE’s main objectives was to challenge the idea that carbon dioxide respiration stopped as soon as the snow fell and the land surface froze,” said Charles Miller, a scientist at NASA’s Jet Propulsion Laboratory in Pasadena, California, and CARVE principal investigator. “The CARVE flights prove that microbial respiration continues in tundra soils months after the surface has frozen.”

Commane and her team then compared simultaneous measurements of atmospheric CO2 and carbon monoxide in order to split their estimates of Alaska’s total carbon budget into contributions from three primary sources, namely the burning of fossil fuels by human populations, the release of gases from wildfires, and microbes decomposing organic matter in the soil. They found that the activity of microbes in the soil contributed more to levels of atmospheric carbon than the burning of fossil fuels, which is generally the prime candidate. Wildfires were found to have provided a major source of carbon during 2013, but typically, their contribution pales in comparison to the impact of soil microbes.

“Tundra soils appear to be acting as an amplifier of climate change,” said co-author Steve Wofsy, a Harvard atmospheric scientist. “We need to carefully monitor what it's doing up there, even late in the year when everything looks frozen and dormant.”

Sam Bonson

Sam is an aspiring novelist with a passion for fantasy and crime thrillers. He is currently working as a content writer, journalist & editor in an attempt to expand his horizons.