The threatening thaw: climate professor on heatwave risks to tipping point of permafrost

Prof Gustaf Hugelius warns wildfires could accelerate release of methane and carbon as vast regions approach irreversible thresholds

Heatwaves and wildfires are not just scorching forests, they are adding to the tipping point risks in the world’s vast permafrost regions, which contain three times more carbon than all the living vegetation on Earth.

This is a major concern for Gustaf Hugelius, a professor at the Bolin Centre of Climate Research at Stockholm University, Sweden, and a leading authority on the risks from thawing tundra and peatlands. In this Q&A, he explains why the world should pay attention.

No, because the thaw of the tundra creates a fundamentally different landscape. There is a lot of pure ice below the ground’s surface. When that melts, the water drains away and the surface collapses. This can create lakes, wetlands or river gullies. These new land forms, which are called thermokarsts, have a completely different hydrology that changes the thermal conductivity of the soil as well as snow conditions in winter. Once you pass the permafrost’s threshold and the ice has gone and the landscape has changed, it is not going to come back for hundreds of years. On a human timescale, those systems have then effectively tipped into a system that will keep emitting carbon for decades or centuries.

Not at a global level. The permafrost region is too big for the full system to go over a threshold at the same time – unless global heating reaches 6C, which will hopefully not happen now. But, as the thaw progresses, there will be many local tipping points that happen in succession. This has started, with some places already passing irreversible tipping points. This adds to the stress on the climate system and by the end of the century the permafrost will become a big emitter in its own right.

We could lose 200 to 300 gigatons of CO2 equivalents if the world warms by between 1.8C and 3.6C by the end of the century. That is many more times than the current emissions of the EU. In even higher warming scenarios, the amount could be close to what the US or even China is emitting today.

A couple of scientific papers forecast very high fluxes of methane, but those extreme scenarios are now considered unrealistic. The release from permafrost thaw is not expected to exceed all human emissions this century, but the broad assumption is that this is a very serious problem, which is worsening the global challenge to reduce emissions.

Methane is about 30 times more potent as a greenhouse gas, though only in the short term because it breaks down more quickly over 10 to 15 years. That makes it a strong and immediate concern and for future generations. Carbon dioxide, by comparison, is less potent but it lingers much longer, which makes it a bigger threat on the timescale of centuries.

It depends on whether the thaw leads to a dry or wet environment. If the exposed landscape is dry – like bare rocks or soil – the microbes will be able to oxidise the carbon in the previously frozen plants into CO2. But if the new landscape is a wetland or a lake, then microbes will not have access to oxygen so they produce methane.