Five tipping points may have exceeded critical levels

Mith the stability of the climate that lasted for a good ten thousand years in the Holocene, it may already be over for good. “The danger is getting closer faster than expected,” says the reassessment by an international research group that has been dealing with the risks of irreversible, possibly abrupt changes – the climate tipping elements – since 2008. With the current warming of 1.1 degrees above the pre-industrial level, the earth has already left a “safe” climate state, and the researchers warn that there is a reasonable likelihood that several threshold values ​​will already be exceeded with the warming of 1.5 degrees targeted in the Paris climate agreement. This may lead to five of the now sixteen tipping points of the world climate being irrevocably thrown out of balance.

Joachim Müller-Jung

Editor in the feuilleton, responsible for the “Nature and Science” department.

A few months after the publication of the sixth assessment report by the Intergovernmental Panel on Climate Change (IPCC), leading climate researchers are once again increasing the warnings of the collapse. Co-author Johan Rockström, the Swedish director of the Potsdam Institute for Climate Impact Research (PIK) and co-chair of the “Earth Commission”, sees the danger posed by the climate tipping elements – the Achilles heel of the earth system – as having been significantly underestimated: “That is definitely more as another warning about climate change,” he says. “It is the first precise and very disturbing analysis of the tipping elements to show us that 1.5 degrees is not simply a climate target, but a true planetary limit.”

The 2 degree target is obsolete

The IPCC had determined that with global warming of two degrees above the pre-industrial level, the probability of triggering tipping points would be “high” and from 2.5 degrees “very high”. It remained unclear what would happen as a result of the warming of 1.5 degrees, which can already be expected in the next eight years given the current trend. The group led by David Armstrong McKay from the Stockholm Resilience Center, Tim Lenton from the University of Exeter and the PIK experts has now re-evaluated all relevant data published since 2008 on the development of possible tipping elements and the old two-degree target, which for decades climate policy has been classified as virtually out of the question. “We accept enormous risks from as little as 1.5 degrees,” says Rockström. “The idea that if we don’t manage 1.5 degrees, then it will just be two degrees, is a dangerous fallacy.” At two degrees, the child has already fallen into the well, so to speak.

In fact, scientific and technical advances in recent years have shown that many of the tipping elements are probably even more sensitive to global warming than initially thought. In addition, the list of possible tipping elements that experts consider endangered has continued to grow worldwide: the list presented by the Science authors now contains nine global elements that are able to throw the entire Earth system out of balance and thus into a new one , uncomfortable situation, as well as seven other tipping elements with regional significance.

The five tipping points, already at the current 1.1 degree warming – at the lower end of the risk assessment uncertainty range, as scientists call it – concern the Greenland and West Antarctic ice sheets, the ocean “circulation pump” in the Labrador Sea, the massive die-off of tropical coral reefs and the thawing of permafrost. According to the evaluation of current data, changes have already started in them, which, although at different speeds, “possibly” already mean that the system is tipping into a different, unstable state. With a warming of 1.5 degrees, this overturning of the five elements would become “probable”. This also shows that the estimates, which are based on huge amounts of data and empiricism from many disciplines, but above all on the calculations of Earth system models, are still subject to considerable uncertainties and data gaps. Nevertheless, the scientists consider the risks ahead to be so predictable that they are sounding the alarm.

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