The world is closer than thought to a "point of no return" after which runaway global heating cannot be stopped, scientists have said. From a report: Continued global heating could trigger climate tipping points, leading to a cascade of further tipping points and feedback loops, they said. This would lock the world into a new and hellish "hothouse Earth" climate far worse than the 2-3C temperature rise the world is on track to reach. The climate would also be very different to the benign conditions of the past 11,000 years, during which the whole of human civilisation developed. At just 1.3C of global heating in recent years, extreme weather is already taking lives and destroying livelihoods across the globe. At 3-4C, "the economy and society will cease to function as we know it," scientists said last week, but a hothouse Earth would be even more fiery. The public and politicians were largely unaware of the risk of passing the point of no return, the researchers said. The group said they were issuing their warning because while rapid and immediate cuts to fossil fuel burning were challenging, reversing course was likely to be impossible once on the path to a hothouse Earth, even if emissions were eventually slashed. It was difficult to predict when climate tipping points would be triggered, making precaution vital, said Dr Christopher Wolf, a scientist at Terrestrial Ecosystems Research Associates in the US. Wolf is a member of a study team that includes Prof Johan Rockstrom at the Potsdam Institute for Climate Impact Research in Germany and Prof Hans Joachim Schellnhuber at the International Institute for Applied Systems Analysis in Austria.

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Iceland in October classified the potential collapse of the Atlantic meridional overturning circulation -- the ocean current system that ferries warm water northward from the tropics and essentially functions as the country's central heating -- as a national security risk, a designation that amounts to a formal reckoning with the possibility that climate change could render the island nation uninhabitable. Several recent studies have found the AMOC far more vulnerable to breakdown than scientists had long assumed. One, analyzing nine models under high-emission scenarios, saw the current weaken and collapse in every single instance; even under the Paris agreement's emission targets, the researchers estimated a 25% chance of shutdown. Stefan Rahmstorf, an oceanographer at Germany's Potsdam Institute for Climate Impact Research and a co-author of that study, said it was "wrong to assume this was low probability." Simulations of a post-collapse world project Icelandic winter extremes plunging to minus-50 degrees Celsius, and sea ice surrounding the country for the first time since Viking settlement. Iceland's national strategy for dealing with AMOC risks is scheduled to be finalized by 2028. The country has also flagged that NASA Goddard, a key source of AMOC modeling, has been targeted for significant staff and budget cuts under the current U.S. administration.

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