Arctic lakes speed up permafrost thawing, global warming

A new study found that a relatively known process called abrupt thawing might speed up Arctic permafrost's expected gradual thawing and then the release of greenhouse gases.

The abrupt thawing takes place under a certain type of Arctic lake, known as a thermokarst lake that forms as permafrost thaws, according to the study published on Friday in the journal Nature Communications.

Its impact on the climate is an influx of permafrost-derived methane into the atmosphere in the mid-21st century, which is not currently accounted for in climate projections.

The Arctic landscape stores one of the largest natural reservoirs of organic carbon in the world in its frozen soils. Once thawed, soil microbes in the permafrost can turn that carbon into the greenhouse gases carbon dioxide and methane.

American and German researchers found that abrupt thawing more than doubles previous estimates of permafrost-derived greenhouse warming.

"We don't have to wait 200 or 300 years to get these large releases of permafrost carbon. Within my lifetime, my children's lifetime, it should be ramping up. It's already happening but it's not happening at a really fast rate right now, but within a few decades, it should peak," said the paper's first author Katey Walter Anthony at the University of Alaska Fairbanks.

They found that the abrupt thaw process increased the release of ancient carbon stored in the soil 125 to 190 percent compared to gradual thawing alone and even in the scenario where humans reduced their global carbon emissions, large methane releases from abrupt thawing are still likely to occur.

The gradual thaw process was thought to have minimal effect as thawed ground would stimulate the growth of plants, which counterbalance the carbon released into the atmosphere by consuming it during photosynthesis.

However, in the presence of thermokarst lakes, permafrost thaws deeper and more quickly. The researchers captured methane bubbling out of 72 locations in 11 thermokarst lakes in Alaska and Siberia.

They found that thermokarst lakes formed when substantial amounts of ice in the deep soil melts to liquid water.

Because the same amount of ice takes up more volume than water, the land surface slumps and subsides, creating a small depression that then fills with water from rain, snow melt and ground ice melt, according to the study.

The water in the lakes speeds up the thawing of the frozen soil along their shores and expands the lake size and depth at a much faster pace than gradual thawing, according to the study.