Arctic’s ‘thermokarst’ lakes may spike methane, CO2 release
Climate scientists are underestimating the methane released from the Arctic permafrost, according to new research from U.S. and German scientists who warn that “abrupt thawing,” a less-understood feature of Arctic melting, may dramatically increase the greenhouse gases released into the atmosphere.
What the research team with the NASA-funded Arctic-Boreal Vulnerability Experiment (ABoVE) found, using a combination of computer models and field observations, are projections that more than double the previous estimates of permafrost-derived global warming.
The study published last week in the journal Nature Communications raises concerns that climate projection models aren’t accurately capturing the abrupt-thawing impacts, but why? The differences lie in the Arctic’s thermokarst lakes, where the gas-trapping permafrost thaws more quickly and deeply.
In the Arctic, the soils loaded with permafrost ice can be up to 80 meters thick. Scientists and many global citizens know that gradual thawing of the permafrost is happening because of warming temperatures tied to human activity. The thaw is releasing carbon dioxide and methane into the atmosphere as the long-frozen, dormant soil microbes and organic matter become active.
That gradual thaw is accounted for in existing climate models, which shape our strategies on climate action. What the models are not accounting for, the new research says, is rapid release because of the lake melt.
Thermokrast lakes are formed when ice deep within the soil melts into water. The ice takes up more volume than melted water, and was solid and embedded in the soil, so when it melts it causes hollows and a subsidence in the land surface. When that land collapses and settles, the lower surface creates a bowl-like depression.
These “bowls” fill with rain water, and snow and ice melt, to form the thermoskart lakes, which then add to the thawing at their own shorelines in a positive feedback loop. The water speeds up the melting of the frozen soil at lake’s edge, increasing the size and depth of the lake at a much faster rate than gradual permafrost thaw does.
“The mechanism of abrupt thaw and thermokarst lake formation matters a lot for the permafrost-carbon feedback this century,” said lead author Katey Walter Anthony at the University of Alaska, Fairbanks, an expert on Arctic methane. “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,” she added.
Walter Anthony and the research team found that abrupt thawing increases the release of the ancient carbon locked in the soil by 125 to 190 percent compared to gradual thawing alone. Even more concerning is that when the finding is considered in the context of future scenarios defined by the Intergovernmental Panel on Climate Change, the abrupt thawing was as important under the moderate reduction of emissions scenario as it was under the extreme business-as-usual scenario.
“This means that even in the scenario where humans reduced their global carbon emissions, large methane releases from abrupt thawing are still likely to occur,” the NASA researchers said.
Images: NASA Goddard
