The climate crisis has pushed the world to the brink of several “catastrophic” tipping points, according to a major study.
It shows that five dangerous turning points may have already been passed due to the 1.1°C global warming caused by humanity to date.
These include the collapse of the Greenland ice cap that eventually led to huge sea-level rise, the collapse of a key North Atlantic current, disruptions to the rains that billions of people depend on for food, and an abrupt melting of carbon-rich permafrost.
At 1.5C warming, the minimum increase now expected, four of the five tipping points move from possible to likely, the analysis says. Also at 1.5°C, another five tipping points become possible, including changes in extensive northern forests and the loss of almost all mountain glaciers.
Overall, the researchers found evidence of 16 tipping points, with the final six requiring at least 2C of global warming to be triggered, the scientists estimate. The turning points would affect timescales ranging from a few years to centuries.
“Earth may have left behind a ‘safe’ climate state beyond 1°C of global warming,” the researchers concluded, since all human civilization evolved at temperatures below that level. Passing a tipping point often helps trigger others and create cascades. However, this is still under investigation and has not been included, meaning the analysis may present the minimal threat.
Prof Johan Rockström, the director of the Potsdam Institute for Climate Impact Research, who was part of the study team, said: “The world is heading towards global warming of 2-3°C.
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“This puts Earth on course to cross several dangerous tipping points that will be catastrophic for people around the world. In order to maintain livable conditions on earth and enable stable societies, we must do everything possible to avoid crossing tipping points.”
dr David Armstrong McKay of the University of Exeter, a lead author on the study, said: “It’s really worrying. There is reason for sadness, but there is still reason for hope.
“The study really underscores why the Paris Agreement target of 1.5°C is so important and must be fought for.
“We’re not saying that because we’re probably going to hit some turning points, all is lost and it’s game over. Every fraction of a degree that we stop beyond 1.5C reduces the likelihood of hitting more tipping points.”
Recent research has shown signs of destabilization in the Amazon rainforest, the loss of which would have “profound” effects on global climate and biodiversity, as well as on the Greenland Ice Sheet and Gulf Stream currents, which scientists refer to as the Atlantic Meridional Overturning Circulation (Amok).
A recent report by the Intergovernmental Panel on Climate Change states that the risk of triggering climate tipping points becomes high at 2°C of global warming.
The analysis, published in the journal Science, evaluated more than 200 previous studies on past turning points, climate observations and modeling studies. A tipping point occurs when a temperature threshold is crossed, leading to inexorable change in a climate system even after global warming ends.
The nine identified global tipping points are: the collapse of the Greenland, West Antarctic, and two parts of the East Antarctic ice sheets, the partial and complete collapse of Amoc, the Amazon die-off, the permafrost collapse, and the loss of Arctic sea ice in winter.
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The assessment of the Amazon tipping point did not take into account the effects of deforestation. “The combination of warming and deforestation could bring that much sooner,” Armstrong McKay said.
Another seven tipping points would have severe regional impacts, including die-offs of tropical coral reefs and changes in the West African monsoon. Other potential tipping points still under investigation are ocean oxygen depletion and major shifts in the Indian summer monsoon.
The scientists define crossing a tipping point as “possible” if its minimum temperature threshold is exceeded and “probable” beyond the central threshold estimate.
Prof Niklas Boers of the Technical University of Munich said: “The review is a timely update of the Earth’s potential tipping elements and the risk of tipping events as warming continues is real.”
He added that much more research is needed to narrow down the critical temperature thresholds, with current estimates being highly uncertain.
Prof Thomas Stocker from the University of Bern said: “The science of tipping points is far from complete – it has only just begun – and much better models are needed to answer this question [of] which level of warming is critical to which tipping point.”
A special IPCC report on climate tipping points was proposed by the Swiss government in May.
Prof Tim Lenton of the University of Exeter, co-author of the analysis, said: “Since I first assessed tipping points in 2008, the list has grown and our assessment of the risk they pose has improved dramatically.
“Our new work provides compelling evidence that the world needs to radically accelerate economic decarbonization. To achieve that, we need to trigger positive social tipping points.”