University of Exeter: Risk of passing multiple climate tipping points escalates above 1.5°C global warming

Even at current levels of global heating the world is already at risk of triggering five dangerous climate tipping points, and risks increase with each tenth of a degree of further warming.

An international research team synthesised evidence for tipping points, their temperature thresholds, timescales, and impacts from a comprehensive review of over 200 papers published since 2008, when climate tipping points were first rigorously defined.

They have increased the list of potential tipping points from nine to sixteen.

The research, published ahead of a major conference “Tipping Points: from climate crisis to positive transformation” at the University of Exeter (12-14 September), concludes we are already in the danger zone for five climate tipping points: melting of the Greenland and West Antarctic ice sheets, widespread abrupt permafrost thaw, collapse of convection in the Labrador Sea, and massive die-off of tropical coral reefs.

Four of these move from “possible” to “likely” at 1.5°C global warming, with five more becoming possible around this level of heating.

Lead author David Armstrong McKay, from Stockholm Resilience Centre, University of Exeter and the Earth Commission, said: “We can see signs of destabilisation already in parts of the West Antarctic and Greenland ice sheets, in permafrost regions, the Amazon rainforest, and potentially the Atlantic overturning circulation as well.

“The world is already at risk of some tipping points. As global temperatures rise further, more tipping points become possible.

“The chance of crossing tipping points can be reduced by rapidly cutting greenhouse gas emissions, starting immediately.”

The Sixth Assessment Report of the Intergovernmental Panel on Climate Change (IPCC), stated that risks of triggering climate tipping points become high by around 2°C above preindustrial temperatures and very high by 2.5-4°C.

The new analysis indicates that Earth may have already left a “safe” climate state when temperatures exceeded approximately 1°C above preindustrial temperatures.

A conclusion of the research is therefore that even the United Nations’ Paris Agreement goal to avoid dangerous climate change by limiting warming to well below 2°C and preferably 1.5°C is not fully safe.

However, the study provides strong scientific support for the Paris Agreement and associated efforts to limit global warming to 1.5°C, as while some tipping points are possible or likely at this temperature level, the risk escalates beyond this point.

To have a 50% chance of achieving 1.5°C and thus limiting tipping point risks, global greenhouse gas emissions must be cut by half by 2030, reaching net-zero by 2050.

Co-author Johan Rockström, co-chair of the Earth Commission and director of the Potsdam Institute for Climate Impact Research, 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, protect people from rising extremes, and enable stable societies, we must do everything possible to prevent crossing tipping points.

“Every tenth of a degree counts.”

Co-author Tim Lenton, director of the Global Systems Institute at the University of Exeter and a member of the Earth Commission, said: “Since I first assessed climate 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 limit the risk of crossing climate tipping points.

“To achieve that, we now need to trigger positive social tipping points that accelerate the transformation to a clean-energy future.

“We may also have to adapt to cope with climate tipping points that we fail to avoid, and support those who could suffer uninsurable losses and damages.”

Scouring paleoclimate data, current observations, and the outputs from climate models, the international team concluded that 16 major biophysical systems involved in regulating Earth’s climate (so-called “tipping elements”) have the potential to cross tipping points where change becomes self-sustaining.

That means even if temperature stops rising, once the ice sheet, ocean or rainforest has passed a tipping point it will carry on changing to a new state.

How long the transition takes varies from decades to thousands of years depending on the system.

For example, ecosystems and atmospheric circulation patterns can change quickly, while ice sheet collapse is slower but leads to unavoidable sea-level rise of several metres.

The researchers categorised the tipping elements into nine systems that affect the entire Earth system, such as Antarctica and the Amazon rainforest, and a further seven systems that if tipped would have profound regional consequences.

The latter include the West African monsoon and the death of most coral reefs around the equator.

Several new tipping elements such as Labrador Sea convection and East Antarctic subglacial basins have been added compared to the 2008 assessment, while Arctic summer sea ice and the El Niño Southern Oscillation (ENSO) have been removed for lack of evidence of tipping dynamics.

Co-author Ricarda Winkelmann, a researcher at the Potsdam Institute for Climate Impact Research and a member of the Earth Commission, said: “Importantly, many tipping elements in the Earth system are interlinked, making cascading tipping points a serious additional concern.

“In fact, interactions can lower the critical temperature thresholds beyond which individual tipping elements begin destabilising in the long run.”