“We show that the risk of some tipping events could increase very sharply under certain global warming excess scenarios,” explains Nico Wunderling, scientist at the Potsdam Institute for Climate Impact Research and lead author of the study, which is published in nature climate change. “Even if we managed to limit global warming to 1.5 degrees after exceeding two degrees, that would not be enough as the risk of triggering one or more global tipping points would still be more than 50 percent In the long term, the risks increase dramatically.”
“In order to effectively prevent all tipping risks, the increase in global average temperature would have to be limited to a maximum of one degree – we are currently at around 1.2 degrees,” says Jonathan Donges, co-leader of the FutureLab on Earth Resilience in the Anthropocene at PIK added. “The latest IPCC report shows that we are most likely on our way to temporarily exceeding the 1.5 degree Celsius temperature threshold.”
The occurrence of at least one tipping event increases with increasing peak temperatures
To arrive at these results, the scientists, along with co-authors from the Earth Commission — a group of leading scientists convened by Future Earth — used various global warming excess scenarios with peak temperatures of two to four degrees and applied them to a set of four interacting Tipping elements: the Greenland Ice Sheet, the West Antarctic Ice Sheet, the Atlantic Meridional Overturning Circulation AMOC, and the Amazon Rainforest. Researchers applied a risk analysis approach based on millions of model simulations to reflect the uncertainties in relevant parameters such as uncertainty in critical temperature thresholds and interaction strengths and interaction structure. Such a volume of simulations would be computationally too expensive to perform based on fully coupled Earth system model simulations. For the different exceedance scenarios, the research team then analyzed the risk of exceeding critical thresholds and the potential to trigger cascading interactions between the four elements, depending on the magnitude and duration of the exceedance and the long-term residual warming.
“We found that the risk of at least one tipping event occurring increases with increasing peak temperatures – already at a peak temperature of three degrees Celsius, more than a third of all simulations showed a tipping event, even when the overshoot duration was severely limited at a peak temperature of four degrees Celsius This risk applies to more than half of all simulations,” explains Nico Wunderling.
Tipping mechanisms in case of overheating
“In particular, the Greenland and West Antarctic Ice Sheets are prone to tipping even with small overshoots, underscoring that they are among the most vulnerable tipping elements. While it would take a long time for ice loss to fully unfold, the temperature levels at which changes trigger such changes could be reached very soon,” says Ricarda Winkelmann, Earth Commissioner and co-lead of the FutureLab on Earth Resilience in the Anthropocene. ” Our actions in the years to come can thus determine the future trajectory of the ice sheets for centuries or even millennia to come.” The other two tipping elements considered in the study, AMOC and Amazon rainforest, have higher critical temperature thresholds, but they would react much faster , once the tipping process has begun, making it much harder to stop their tipping process, once triggered by a temporary global warming overshoot.
Current mitigation policies are expected to result in global warming of 2 to 3.6 degrees Celsius by the end of this century. “That is not enough. While a temporary temperature excess would definitely be better than reaching a peak temperature and staying there, some of the impacts of the excess can cause irreversible damage in a high climate risk zone, and that’s why low temperature excesses are so key here,” explains Jonathan Donges. Ricarda Winkelmann adds: “Every tenth of a degree counts. We must do everything we can to limit global warming as quickly as possible.”
Materials provided by Potsdam Institute for Climate Impact Research (PIK). Note: Content can be edited for style and length.