Four tipping points for the global climate could be reached by 2030. This is the result of an analysis by an international group of climate researchers. Two of these tipping points concern the Greenland Ice Sheet and the West Antarctic Ice Sheet, respectively. Crossing the threshold could lead to dynamics that will allow the ice sheets to continue to melt even if the temperature on Earth does not increase any further, reports the team led by David Armstrong McKay and Timothy Lenton from the University of Exeter (UK) in the journal “Science”.
Lenton is one of the researchers who first identified tipping points for the global climate in 2008. They defined tipping points as “a critical threshold at which a tiny perturbation can qualitatively alter the state or evolution of a system”.
For example, when a glacier loses altitude as it melts, its surface moves into lower, warmer layers of air, which accelerates melting. Beyond the tipping point, feedback processes can ensure that development becomes unstoppable. In the case of ocean currents like the Gulf Stream, changes can have a huge impact on climate.
Since 2008, more than 200 studies on the topic of “tipping points” have been published. Armstrong McKay, Lenton and colleagues carefully studied them and based them on an updated model of climate tipping points. They identify nine tipping points relevant to global climate and seven tipping points that have wide-ranging regional impacts.
The researchers estimate that when global warming reaches an average of 1.5 degrees Celsius compared to the pre-industrial era, four tipping points will be reached: the Greenland and West Antarctic ice sheets, the dying of tropical coral reefs and the thawing of the permafrost.
Based on developments in recent years, they predict that 1.5 degrees will become reality as early as 2030. If all the measures currently planned by politicians were implemented, the global temperature could be limited to a rise of 1.95 degrees by 2100. However, measures introduced so far would only limit warming to 2.6 degrees.
Johan Rockström of the Potsdam Institute for Climate Impact Research is quoted as saying in a statement from his institute that “the earth is right on course to cross several dangerous threshold values that would have catastrophic consequences for people around the world.” Rockström is another co-author of the study.
As global warming approaches two degrees, further tipping points become possible: the melting of mountain glaciers outside the polar regions and the dying of the boreal coniferous forest in the southern distribution area. However, the changes in the Gulf Stream, which is part of the Atlantic overturning circulation and which ensures mild temperatures in Europe, are particularly relevant for Europe: According to the researchers, a collapse of a Gulf Stream branch south of Greenland is becoming increasingly likely, which will also affect the overturning circulation. However, it is only likely that the entire Atlantic circulation – and with it the Gulf Stream – could collapse if the global temperature rises by more than four degrees.
In the case of the ice sheets, too, the researchers assume a process of 2000 years (West Antarctic ice sheet) or 10,000 years (Greenland ice sheet) until they melt completely. In other parts of Antarctica, the tipping points would only be reached with global warming of three to seven degrees. However, if all polar ice caps melted, global sea levels would rise by about 66 meters. Other consequences of climate change could also have catastrophic effects on life on earth.
Rockström therefore warns: “In order to maintain good living conditions on earth, to protect people from increasing extremes and to enable stable societies, we must do everything we can to prevent tipping points from being exceeded – every tenth of a degree counts.”
