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A study from the University of Hamburg's CLICCS suggests that the risk of climate tipping points, such as permafrost thaw and Amazon rainforest destruction triggering chain reactions, is lower than previously thought. While this offers cautious optimism, there remains a significant risk under current climate policies, with a 50% chance that nine of 16 critical tipping points could be exceeded. These include coral dieback and Greenland ice sheet thawing. The study highlights that ambitious climate protection could substantially mitigate this risk. Researchers used innovative climate models to analyze scenarios and probabilities.
The risk of climatic tipping points like thawing permafrost and the destruction of the Amazon rainforest triggering each other in a chain reaction is lower than previously assumed. These grounds for cautious optimism can be found in a new study from the University of Hamburg’s Cluster of Excellence CLICCS. But at the same time, it shows: there is a risk of an extreme scenario under the current climate policy. Pursuing more ambitious climate protection could significantly reduce that risk.
The Earth system is like a mobile over a baby’s crib, with individual elements like the global ice sheets, massive forests, and ocean currents all connected and delicately balanced. If any one element exceeds a certain threshold, this equilibrium can be abruptly and irrevocably lost. Climate researchers refer to these conditions as tipping points. Many fear that if one element exceeds its tipping point, it will unavoidably destabilize other elements, which could set off an uncontrollable domino effect.
The new study, just released by CLICCS researcher Jakob Deutloff and colleagues in the journal Earth System Dynamics, takes a closer look at the probability of 16 such elements exceeding their tipping points in a range of future scenarios – in other words, depending on how global greenhouse-gas emissions develop by the year 2500. In this regard, it focuses on those tipping points that directly affect Earth’s carbon cycle, including permafrost, which could release tremendous amounts of methane and CO2 when it thaws, and the Amazon rainforest, which is dying out in response to increasingly arid conditions, also releasing carbon in the process. These carbon tipping elements are widely considered to be potential triggers for a dangerous chain reaction, since the related emissions further accelerate global warming, which could lead to further tipping points being exceeded.
The good news: “These carbon tipping elements are unlikely to set off such a domino effect,” as Jakob Deutloff explains. His calculations indicate that the additional temperature increase in connection with carbon released by the permafrost and Amazon will be relatively low – compared to the warming caused by anthropogenic emissions. “It’s ultimately up to us which tipping points are exceeded and whether a situation arises that we can no longer control.”
At the same time, under the current climate policy the probability of several critical tipping points being exceeded is high: according to the researchers’ most conservative estimate, there’s more than a 50 percent chance that nine of the 16 tipping points will be exceeded. Those with particularly high probabilities include coral reef dieback, the thawing of Greenland’s ice sheets, and the complete loss of the West Antarctic Ice Sheet.
But the study also shows that a rapid and systematic transition to sustainable scenarios in which greenhouse-gas emissions are dramatically reduced can reduce the probability: “More intensive climate protection can significantly reduce the risk of an irreversible development,” says Deutloff.
For the study, the experts combined two climate models in an unconventional way: a simplified model (FaIR) that is well-suited to displaying the connections between emissions and global mean temperature; and a carbon tipping elements model (CTEM), which reflects the additional emissions that would be released if the Amazon and permafrost exceeded their critical threshold values. The researchers simulated thousands of possible developments in order to calculate the probabilities of the respective scenarios. The study also draws on a comprehensive analysis of the extant academic literature on climate tipping points.
Jakob Deutloff
University of Hamburg
Center for Earth System Research and Sustainability (CEN)
Cluster of Excellence “Climate, Climatic Change, and Society” (CLICCS)
Tel.: +49 40 42838-8121
E-Mail: jakob.deutloff@uni-hamburg.de
Deutloff J, Held H, Lenton TM (2025): High probability of triggering climate tipping points under current policies modestly amplified by Amazon dieback and permafrost thaw, Earth System Dynamics, doi.org/10.5194/esd-16-565-2025
https://esd.copernicus.org/articles/16/565/2025/
https://www.cliccs.uni-hamburg.de/
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