Melting permafrost is doubling greenhouse warming from the tundra.

Nature reports on a vicious cycle that’s making things uncomfortable in the Arctic – a release of gases from melting permafrost that’s literally collapsing, freeing up much deeper layers of trapped carbon dioxide than expected:

Current models of greenhouse-gas release and climate assume that permafrost thaws gradually from the surface downwards. Deeper layers of organic matter are exposed over decades or even centuries, and some models are beginning to track these slow changes.

But models are ignoring an even more troubling problem. Frozen soil doesn’t just lock up carbon — it physically holds the landscape together. Across the Arctic and Boreal regions, permafrost is collapsing suddenly as pockets of ice within it melt. Instead of a few centimetres of soil thawing each year, several metres of soil can become destabilized within days or weeks. The land can sink and be inundated by swelling lakes and wetlands.

Returning to field sites in Alaska, for example, we often find that lands that were forested a year ago are now covered with lakes. Rivers that once ran clear are thick with sediment. Hillsides can liquefy, sometimes taking sensitive scientific equipment with them.

Predictions suggest that slow and steady thawing will release around 200 billion tonnes of carbon over the next 300 years under a business-as-usual warming scenario3. That’s equivalent to about 15% of all the soil carbon currently stockpiled in the frozen north.

But that could be a vast underestimate. Around 20% of frozen lands have features that increase the likelihood of abrupt thawing, such as large quantities of ice in the ground or unstable slopes.

Worse, the most unstable regions also tend to be the most carbon-rich. For example, 1 million square kilometres of Siberia, Canada and Alaska contain pockets of Yedoma — thick deposits of permafrost from the last ice age4. These deposits are often 90% ice, making them extremely vulnerable to warming. Moreover, because of the glacial dust and grasslands that were folded in when the deposits formed, Yedoma contains 130 billion tonnes of organic carbon — the equivalent of more than a decade of global human greenhouse-gas emissions.

Regions that are vulnerable to abrupt thawing need more boreholes, long-term observatories and experiments. Field measurements should quantify how much CO2 and methane is released to the atmosphere as frozen soils are disturbed and recover.

Because abrupt thawing occurs at fine spatial scales, detailed process models of these dynamics could be impractical to run directly within Earth-system models. Frameworks must be developed to understand and quantify the effect of these fine-scale processes at the global level.