The climate crisis has driven the world to the brink of several “catastrophic” tipping points, according to a major study.
It shows that five dangerous tipping points may already have been passed due to the 1.1 degrees of human-caused global warming to date.
These include the collapse of the Greenland ice sheet, which ultimately caused a huge rise in sea levels, the collapse of a key current in the North Atlantic, disrupting rainfall that billions of people depend on for food, and a precipitous melting of carbon-rich permafrost.
At 1.5 degrees of warming, the smallest increase now expected, four of the five tipping points move from possible to probable, the analysis reads. Also at 1.5 C, five more tipping points become possible, including changes in large northern forests and the loss of nearly all mountain glaciers.
In total, the researchers found evidence for 16 tipping points, with the last six requiring global warming of at least 2C to be triggered, according to the researchers’ estimates. The tipping points will take effect on timescales varying from a few years to centuries.
“Earth may have left a ‘safe’ climate state beyond 1C of global warming,” the researchers concluded, with all of human civilization having evolved in temperatures below this level. Passing one tipping point will often help trigger others, producing cascades. However, this is still being studied and was not included, meaning the analysis may pose the least danger.
Prof Johan Rockström, the director of the Potsdam Institute for Climate Impact Research, who was part of the research team, said: “The world is heading for 2-3C of global warming.
“This puts Earth on course to cross several dangerous tipping points that will be catastrophic for people around the world. To maintain livable conditions on Earth and enable stable societies, we must do everything we can to prevent crossing tipping points.”
Dr. David Armstrong McKay of the University of Exeter, a lead author of the study, said: “It is really worrying. There is cause for sadness, but there is also still cause for hope.
“The study really underpins why the Paris Agreement’s goal of 1.5C is so important and must be fought for.
“We don’t say that, because we will probably hit some tipping points, everything is lost and the game is over. Every fraction of a degree that we stop beyond 1.5 C reduces the likelihood of hitting multiple tipping points.”
Recent research has shown signs of destabilization in the Amazon rainforest, the loss of which would have “profound” implications for global climate and biodiversity, as well as the Greenland ice sheet and the Gulf Stream currents, which scientists call the Atlantic meridional overturning circulation (Amoc).
A recent report by the Intergovernmental Panel on Climate Change said the risk of triggering climate tipping points will be high with 2C of global warming.
The analysis, published in the journal Science, assessed more than 200 previous studies of past tipping points, climate observations and modeling studies. A tipping point is when a temperature threshold is exceeded, leading to unstoppable changes in a climate system, even if global warming ceases.
The nine identified global tipping points are: the collapse of Greenland, West Antarctica and two parts of the East Antarctic ice sheets, the partial and total collapse of Amoc, the collapse of the Amazon, permafrost collapse and winter sea loss in the Arctic.
The Amazon tipping point assessment did not include the effects of deforestation. “The combination of the warming and the deforestation could bring it much faster,” Armstrong McKay said.
Another seven tipping points would have severe regional effects, including the extinction of tropical coral reefs and changes in the West African monsoon. Other potential tipping points still under study include the loss of oxygen from the ocean and major changes in the Indian summer monsoon.
The researchers define crossing a tipping point as “possible” when its minimum temperature threshold is passed and “probable” beyond the central threshold estimate.
Prof Niklas Boers, of the Technical University of Munich, said: “The revision is a timely update on Earth’s potential overturning elements and the threat of overturning events under further warming is real.”
He added that much more research was needed to narrow down the critical temperature thresholds, where current estimates remain highly uncertain.
Professor Thomas Stocker, from the University of Bern, said: “The science of tipping points is far from finished – it has barely begun – and much better models are needed to address the question [of] which heating level is decisive for which tipping point.”
A special IPCC report on climate tipping points was proposed in May by the Swiss government.
Prof Tim Lenton of the University of Exeter, a 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 increased dramatically.
“Our new work provides compelling evidence that the world needs to radically accelerate the decarbonization of the economy. To achieve that, we need to trigger positive social tipping points.”