You have probably heard of permafrost, and that it is critical that it thaws as it could release carbon into the atmosphere? Which, in turn, could increase global warming? But is it a "ticking time bomb" that remains more or less inactive until a certain threshold is reached for warming, to then go off?
An international group of scientists and experts have investigated this. They found no evidence of a global tipping element associated with permafrost. Instead, they found that permafrost-affected soil is thawing in line with global warming, and this is occurring locally or regionally.
The study led by Alfred Wegener Institute is published in Nature Climate Change, and Sebastian Westermann from the Department of Geosciences, University of Oslo is one of the authors.
Significant landmass is subject to permafrost in the Northern Hemisphere
Approximately 15% of the landmass in the Northern Hemisphere is covered by permafrost. The definition of permafrost is ground, soil, and rock where the temperature does not exceed 0 degrees Celsius over the course of two consecutive years. Permafrost contains large amounts of organic carbon in the form of dead plant material.
As long as the ground is frozen, the carbon is fixed in the soil, but when it thaws, microorganisms can break down and release the carbon into the atmosphere as the greenhouse gases, carbon dioxide and methane. Consequently, increasing global temperatures could activate this vast reservoir and exacerbate climate change through additional greenhouse gas emissions.
Is thawing permafrost a tipping element, and does it have a threshold value?
Several have argued that thawing permafrost is a "ticking carbon time bomb." This is based on the assumption that permafrost, like the Greenland ice sheet, is one of several tipping elements in the Earth system. According to this view, permafrost initially only has gradual thawing in response to global warming, but once a critical threshold value is exceeded, the thawing processes will suddenly start reinforcing each other, leading to a rapid and irreversible collapse of permafrost across the Arctic.
While many have speculated that the thawing permafrost may amplify itself when it becomes warm enough, it has not been definitively established to date whether such a threshold value exists or what the corresponding temperature limit is.
Self-reinforcing effects occur locally, not as global tipping elements
In the new study, researchers have investigated the significance of permafrost for the climate. Based on available scholarly literature and their own data analysis, they have assessed all current findings on thawing processes. They have examined whether, and if so, on what scale – local, regional, global – they can lead to self-sustaining thawing. And whether they can therefore act as a tipping element in relation to a certain level of warming. One of the researchers behind the study, Sebastian Westermann, Professor at the Department of Geosciences, explains the results of the work:
– Although there are geological, hydrological, and physical processes that are self-reinforcing and in many cases irreversible, they only have effects on permafrost locally or regionally. An example is the formation of so-called thermokarst lakes. The ice in the permafrost soil melts and forms depressions where meltwater accumulates, which then increases the warming of the permafrost under the water and causes a self-reinforcing thawing process in and around the lake.
The researchers also found similar self-reinforcing feedbacks in other permafrost-related processes, such as the loss of boreal forests due to fires - but again, only at the local to regional level.
– There is no evidence of self-reinforcing internal processes that would affect the entire permafrost at a certain degree of global warming and accelerate its thawing globally. It is therefore misleading to portray permafrost as a global tipping element, says Westermann.
Arctic permafrost is heterogeneous and is affected differently
However, that does not mean there is no cause for concern when it comes to Arctic permafrost. On the contrary, the study clearly demonstrates that the permafrost zone is highly heterogeneous. Consequently, many small, local tipping elements will be crossed at different times, and warming levels will accumulate over time. As a result, global thawing of permafrost will not be a gradual increase followed by a sudden surge, but will intensify in line with global warming. Eventually, it will lead to the complete loss of permafrost when global warming reaches five to six degrees Celsius.
It also means that more and more regions will inevitably be affected by thawing already now or in the near future, according to the research team. In other words, there is no safety margin for warming, as the concept of a tipping point with a specific threshold value might imply. Therefore, it is crucial to improve ongoing monitoring of permafrost-affected regions and gain a deeper understanding of the processes. They must be included in climate models to further reduce uncertainties in climate projections, according to the research team.
Regarding the loss of permafrost and the release of greenhouse gases into the atmosphere, the researchers state in a press release about the study that the faster humanity achieves net-zero emissions, the more regions with permafrost can be preserved as unique habitats and carbon reservoirs.
The scientific article:
Nitzbon, J., Schneider von Deimling, T., Aliyeva, M., Chadburn, S. E., Grosse, G., Laboor, S., Lee, H., Lohmann, G., Steinert, N., Stuenzi, S., Werner, M., Westermann, S., & Langer, M.. 2024. No respite from permafrost-thaw impacts in the absence of a global tipping point. Nat. Clim. Chang. https://doi.org/10.1038/s41558-024-02011-4
See also:
Thawing permafrost: Research suggests it's not a climate tipping point, but nevertheless has far-reaching impacts. Phys.org, 3. June. 2024 (press release Alfred Wegener Institute)