From The Guardian:

The climate crisis has driven the world to the brink of multiple “disastrous” tipping points, according to a major study.

It shows five dangerous tipping points may already have been passed due to the 1.1 C (2 F) of global heating caused by humanity to date.

These include the collapse of Greenland’s ice cap, eventually producing a huge sea level rise, the collapse of a key current in the north Atlantic, disrupting rain upon which billions of people depend for food, and an abrupt melting of carbon-rich permafrost.

At 1.5 C of heating, the minimum rise now expected, four of the five tipping points move from being possible to likely, the analysis said. Also at 1.5 C, an additional five tipping points become possible, including changes to vast northern forests and the loss of almost all mountain glaciers.

In total, the researchers found evidence for 16 tipping points, with the final six requiring global heating of at least 2 C to be triggered, according to the scientists’ estimations….

“The Earth may have left a ‘safe’ climate state beyond 1 C global warming,” the researchers concluded, with the whole of human civilisation having developed in temperatures below this level. Passing one tipping point is often likely to help trigger others, producing cascades. But this is still being studied and was not included, meaning the analysis may present the minimum danger.

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 2-3 C of global warming.

“This sets Earth on course to cross multiple dangerous tipping points that will be disastrous for people across the world. To maintain liveable conditions on Earth and enable stable societies, we must do everything possible to prevent crossing tipping points.”

Dr David Armstrong McKay at the University of Exeter, a lead author of the study, said: “It’s really worrying. There are grounds for grief, but there are also still grounds for hope.

“The study really underpins why the Paris agreement goal 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 tipping points, everything is lost and it’s game over. Every fraction of a degree that we stop beyond 1.5 C reduces the likelihood of hitting more tipping points.”

The analysis, published in the journal Science, assessed more than 200 previous studies on past tipping points, climate observations and modelling studies. A tipping point is when a temperature threshold is passed, leading to unstoppable change in a climate system, even if global heating ends….

Prof Tim Lenton at 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 must radically accelerate decarbonising the economy. To achieve that, we need to trigger positive social tipping points.”