Permafrost covers about a quarter of the Northern Hemisphere's landmass and holds significant organic carbon as dead plant matter. When permafrost thaws, microorganisms break down this matter, releasing carbon dioxide and methane into the atmosphere. Rising global temperatures could activate this reservoir, worsening climate change through additional emissions. Public debate often describes this as a "ticking carbon timebomb," assuming permafrost will gradually thaw and then suddenly collapse once a critical threshold is reached. The research team, led by Dr. Jan Nitzbon from the Alfred Wegener Institute, aimed to clarify whether such a threshold exists and what the temperature limit might be.
"In fact, the idea of permafrost being a global tipping element is a controversial one in the research community. The IPCC also pointed out this uncertainty in its latest Assessment Report," said Nitzbon.
"Our goal was to close this gap in our knowledge. For our study, we compiled the available academic literature on those processes that can influence and accelerate the thawing of permafrost. Combining it with our own data analysis, we assessed all current findings on thawing processes in terms of whether and, if so, on which spatial scale - local, regional, global - they could lead to self-perpetuating thawing and therefore to a 'tipping' in connection with a given level of warming."
The findings indicate that while there are self-amplifying processes, they act only locally or regionally. An example is the formation of thermokarst lakes, where melting ice creates depressions filled with meltwater. These dark lakes absorb solar energy, further warming the permafrost underneath and creating a self-sustaining thawing process. Similar feedbacks were found in other permafrost-related processes, like the loss of boreal conifer forests due to fire, but again, only at local to regional scales.
"There is no evidence of self-amplifying internal processes that, from a certain degree of global warming, affect all permafrost and accelerate its thawing globally," Nitzbon explained.
"Moreover, the projected release of greenhouse gases wouldn't lead to a global upsurge in warming by the end of the century. As such, portraying the permafrost as a global tipping element is misleading."
The study shows that permafrost is very heterogeneous. Numerous small, local tipping points will be exceeded at different times and warming levels, accumulating over time. Global permafrost thaw will intensify with global warming, leading to total loss once warming reaches 5 to 6 degrees Celsius.
"That means more and more regions are already or soon will be inevitably affected by thawing," Nitzbon said.
"In other words, there is no safety margin of warming - as the image of the tipping point suggests - that we can still exploit as long as we don't exceed the threshold value. That's why we need to keep a close eye on the permafrost regions through even better monitoring, gain a better grasp of the processes involved, and represent them in climate models to further reduce the sources of uncertainty. And one more thing is clear with regard to the greenhouse-gas emissions-based permafrost loss: the sooner that humankind can achieve net-zero emissions, the more regions can be preserved as unique habitats and carbon reservoirs."
Research Report:No respite from permafrost-thaw impacts in the absence of a global tipping point
Related Links
Alfred Wegener Institute, Helmholtz Centre for Polar and Marine Research
Beyond the Ice Age
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