Scientists have warned that the world is moving closer to a “point of no return” beyond which runaway global heating cannot be halted. Continued warming could trigger climate tipping points, setting off a cascade of feedback loops that would lock the planet into a “hothouse Earth” state far more severe than the 2-3C temperature rise currently projected, they said.
Writing in the journal One Earth, an international team said that crossing even some thresholds could commit the planet to a hothouse trajectory. The researchers, including Dr Christopher Wolf of Terrestrial Ecosystems Research Associates, Prof Johan Rockström of the Potsdam Institute for Climate Impact Research, and Prof Hans Joachim Schellnhuber of the International Institute for Applied Systems Analysis, noted that policymakers and the public remain largely unaware of the risks. “It is likely that global temperatures are as warm as, or warmer than, at any point in the last 125,000 years,” Wolf said, adding that carbon dioxide levels are probably the highest in at least 2m years.
The assessment synthesised recent findings on climate feedback loops and 16 tipping elements, including the Greenland and Antarctic ice sheets, mountain glaciers, polar sea ice, sub-Arctic forests, permafrost, the Amazon rainforest, and the Atlantic meridional overturning circulation (Amoc), a system of ocean currents that strongly influences global climate. The scientists said tipping may already be under way in Greenland and west Antarctica, with permafrost, mountain glaciers and the Amazon appearing close to destabilisation.
Prof William Ripple of Oregon State University, who led the analysis, said the Amoc was already showing signs of weakening, which could increase the risk of Amazon dieback. “Carbon released by an Amazon dieback would further amplify global warming and interact with other feedback loops,” he said. “We need to act quickly on our rapidly dwindling opportunities to prevent dangerous and unmanageable climate outcomes.”
Prof Tim Lenton of the University of Exeter, an expert on tipping points, said profound risks already exist on the current trajectory. “We don’t need to be heading towards a hothouse Earth for there to be profound risks to humanity and our societies – these will already be upon us if we continue to 3C global warming.” The scientists previously warned in 2018 that a hothouse Earth could see global temperatures remain significantly above 4C for thousands of years, driving a huge rise in sea levels that would drown coastal cities.
