Slow-Freezing Alaska Soil Driving Surge in CO2 Emissions

Alaska’s soils are taking far longer to freeze over as winter approaches than in previous decades, resulting in a surge in carbon dioxide emissions that could portend a much faster rate of global warming than scientists had previously estimated, according to new research.

Measurements of carbon dioxide levels taken from aircraft, satellites and on the ground show that the amount of CO2 emitted from Alaska’s frigid northern tundra increased by 70% between 1975 and 2015, in the period between October and December each year.

Researchers said warming temperatures and thawing soils were the likely cause of the increase in CO2 at a time of year when the upper layers of soil usually start freezing over as winter sets in.

In the Arctic summer, the upper level of soil, which sits above a vast sheet of permafrost that covers much of Alaska, thaws out and decomposing organic matter starts to produce CO2. From October, colder temperatures help freeze the soil again, locking up the CO2.

Alaska’s warming autumns and winters are altering this process.  Whereas soils 40 years ago took about a month to completely freeze over, the process can now take three months or longer.  In some places in the state, the soil is not freezing until January, particularly if there is a layer of insulating snow.

The result is a huge and continuing expulsion of CO2, a planet-warming gas, into the atmosphere.  In 2013, a particularly warm year racked by wildfires in Alaska, around 40m more tons of CO2 was given out by soils than absorbed by vegetation – an amount four times larger than that emitted by the state’s use of fossil fuels.

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