Permafrost thaw: Research suggests not a climate tipping point, but nonetheless has far-reaching consequences

Permafrost soils store large amounts of organic carbon and are often described as a critical tipping point in the Earth system that, once global warming reaches a certain level, collapses suddenly and on a global scale. Yet this image of a ticking time bomb, which remains relatively silent until it explodes at a certain level of warming, is controversial within the research community.

Based on currently available scientific data, the picture is misleading, as an international team led by the Alfred Wegener Institute showed in a recently published study.

According to their findings, there is no single global tipping point; rather, there are many local and regional phenomena, which “flip” at different times, producing cumulative effects and causing permafrost to thaw at the rate of climate change. It is therefore all the more important to take decisive action today if our goal is to preserve as much permafrost as possible. The study was published in the journal Climate change.

Permafrost covers about a quarter of the landmass in the Northern Hemisphere and stores huge amounts of organic carbon in the form of dead plant matter. As long as it remains frozen, this material remains intact, but when permafrost thaws, microorganisms begin to break it down, releasing large amounts of carbon into the atmosphere in the form of CO.₂ and methane.

As a result, rising global temperatures could activate this enormous reservoir and significantly worsen climate change through additional emissions. Therefore, in public debate you will frequently encounter the idea of ​​a “carbon time bomb”.

This is based on the hypothesis that permafrost, like the Greenland ice sheet, is one of many tipping elements in the Earth system. From this point of view, permafrost will initially only experience a gradual thaw in response to global warming; then, once a critical threshold is exceeded, thawing processes will suddenly begin to amplify each other, leading to the rapid and irreversible collapse of permafrost throughout the Arctic.

Although many have speculated about the possibility of this type of thaw scenario, to this day it remains unclear whether there actually is such a threshold value and, if so, what the corresponding temperature limit is.

An international research team led by Dr. Jan Nitzbon from the Alfred Wegener Institute at the Helmholtz Center for Polar and Marine Research (AWI) has now gotten to the bottom of this question.

“In fact, the idea that permafrost is a global tipping point is controversial in the research community. The IPCC also highlighted this uncertainty in its latest assessment report,” explains the AWI expert.

“Our goal was to fill this gap in our knowledge. For our study, we compiled the available academic literature on processes that may influence and accelerate the thawing of permafrost. Combining it with our own data analysis, we We evaluated all current findings on thawing processes in terms of whether and, if so, at what spatial scale – local, regional, global – they could lead to self-sustaining thawing and thus related “tipping”. with a given warming level.

The conclusions of the study are clear: there are indeed geological, hydrological and physical processes which are self-amplifying and, in certain cases, are irreversible; however, these only act locally or regionally. An example: the formation of what we call thermokarst lakes. Here, the ice inside the permafrost soils melts, creating depressions.

Melt water accumulates on their surface, producing a dark lake that absorbs large amounts of solar energy. This in turn intensifies the warming of permafrost underwater, creating a self-sustaining thawing process in and around the lake. They also found similar amplifying feedbacks in other permafrost-related processes, such as the loss of boreal coniferous forests to fires, but again, only at a local or regional scale.

“There is no evidence of self-amplifying internal processes that, from a certain degree of global warming, affect the entire permafrost and accelerate its thawing on a global scale,” says Nitzbon.

“Moreover, projected greenhouse gas emissions will not lead to an increase in global warming by the end of the century. As such, describing permafrost as a global tipping point is misleading.”

But this does not mean that Arctic permafrost is not of concern: on the contrary, the study clearly shows that the permafrost zone is very heterogeneous. Therefore, many small local tipping points will be exceeded at different times and levels of warming, accumulating over time.

As a result, the overall thaw of permafrost will not constitute a gradual increase followed by a sudden surge; on the contrary, it will intensify as global warming continues, leading to the total loss of permafrost once global warming reaches 5 to 6 degrees Celsius.

“This means that more and more regions are already or will soon be inevitably affected by the thaw,” explains the AWI researcher.

“In other words, there is no margin of safety on warming – as the tipping point image suggests – that we can still exploit as long as we do not exceed the threshold value.

“This is why we need to closely monitor permafrost regions by monitoring them even better, better understand the processes involved and represent them in climate models in order to further reduce sources of uncertainty. And one thing is clear about concerns the loss of permafrost due to greenhouse gas emissions: the sooner humanity can reach net zero emissions, the more regions can be preserved as unique habitats and carbon reservoirs.