A new global mapping project has pinpointed regions where, due to global warming, the risk is high for thawing permafrost to release carbon as greenhouse gases.
Northern permafrost soils store twice as much carbon as is currently in the atmosphere, but the future of this carbon store is uncertain.
"The soil organic matter that's in permafrost, when you're thawing it out-like vegetables from your freezer-will start to decompose and release greenhouse gases," said David Olefeldt, the project's lead researcher and an expert in landscape carbon cycling in the Department of Renewable Resources.
"The most dramatic changes are likely to occur where permafrost thaw is accompanied by land surface collapse."
Land surface collapse due to permafrost thaw is known as thermokarst, and occurs when thawing soil contains large amounts of ice. Thermokarst can lead to more than two dozen distinct collapse landforms, including gullies, slumps, wetlands and lakes. Each type affects greenhouse gas emissions in its own way, and up until now no one has been able to account for all of them at the global scale.
"From local work (individual scientists' field projects), we know that the development of these thermokarst landforms can lead to very large greenhouse gas emissions," said Olefeldt. "Furthermore, thermokarst often leads to wet conditions that favour methane emissions-a much more potent greenhouse gas than carbon dioxide."
Scaling results from the local to the global has so far been hindered by both the diversity of the thermokarst landforms and a lack of information on where these thermokarst landforms are most likely to occur in a warming world.
To start figuring this out, Olefeldt and scientists from the Permafrost Carbon Network (an international group that synthesizes existing research) grouped thermokarst landforms into a few categories and linked their occurrence to certain landscape characteristics for which information exists. By layering available maps of topography, soil type and permafrost conditions, they ended up with a new map that shows which regions are good candidates for having lots of thermokarst landforms.
The study concluded that about 20 per cent of the globe's northern permafrost region is potential thermokarst landscape-an area about five times larger than Alberta.
"Now that we have an assessment of where these landforms occur, scientists can play around with different assumptions, such as how fast will they expand and how fast the soil organic matter will turn into greenhouse gases," said Olefeldt.
That's especially important since last December's Paris Agreement set limits on the amount of greenhouse gases the world's countries can release, in order to hold the average global temperatures to below a 2C increase compared to pre-industrial times. "If there are large emissions from thawing permafrost soils, we may overshoot such targets even if fossil fuel emissions are reduced," said Olefeldt.
"The map allows us to estimate how much greenhouse gases will be released into the atmosphere due to permafrost thaw and hopefully we find that it is less of a problem than what local field studies have indicated."
The thermokarst landscape map is available to anyone through the online site hosted by the U.S. Department of Energy's Oakridge National Laboratory in Tennessee. The paper that explains the study is published in Nature Communications.