‘Abrupt thaw’ of permafrost beneath lakes could significantly affect climate change models

James Marshall
August 19, 2018

In the latest study, researchers monitored the levels of greenhouse gases released by thawing permafrost beneath thermokarst lakes and their impact on climate change. Permafrost is already thawing in some parts such as lakes beneath the Arctic.

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

Scientists have anxious for years that rising temperatures will free carbon trapped in frozen soil in the Arctic, accelerating the pace of climate change - but now they believe abrupt thawing below lakes is even more risky.

As Earth's climate continues to warm and permafrost thaws, soil microbes in the permafrost can turn that carbon into the greenhouse gases carbon dioxide and methane, which then enter into the atmosphere and contribute to climate warming.

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

The results of the study also suggest that now is the time that the emissions from thermokarst lakes are also included into global climate models, since they are now the hotspots of permafrost carbon release. "Within my lifetime, my children's lifetime, it should be ramping up".

For the study, Katey Walter, lead author of the study, and her colleagues studied several thermokarst lakes in Alaska and Siberia over a 12-year long period. The mechanism of this rapid thawing process indicates that this ancient carbon releases 125 to 190 percent faster than it does from simple, gradual thawing by itself.

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. "When the lakes form, they flash-thaw these permafrost areas", said Walter Anthony, who is an associate professor at the UAF's Water and Environmental Research Center.

Methane bubbles are trapped in the ice on a pond near Fairbanks, Alaska. 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. Then, they used this data to make sure the models they were building were on the right track.

But when that happens below thermokarst lakes, the process is even grimmer because the water at the surface speeds up the melting below. However, a process begins in the event that the permafrost thaws out - soil microbes located in the permafrost convert the carbon into carbon dioxide and methane.

Because the thermokarst lakes are relatively small and scattered throughout the Arctic landscapes, computer models of their behavior are not now incorporated into global climate models.

"You can't stop the release of carbon from these lakes once they form", Walter Anthony said. They argue that not including them in global climate models overlooks their feedback effect, which occurs when the release of greenhouse gases from permafrost increases warming.

Other reports by Click Lancashire

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