Risk of multiple climate tipping points escalates above 1.5°C global warming

According to a significant new analysis published in the journal Science, if global temperature increases by more than 1.5°C beyond pre-industrial levels, many climate tipping points might be set off. Five severe climatic tipping points are currently possible at the current rate of global warming, and the dangers are worse with every additional tenth of a degree of warming.

An extensive analysis of more than 200 publications published since 2008, when climatic tipping points were first properly defined, allowed an international research team to synthesize the evidence for tipping points, their temperature thresholds, timelines, and implications. From nine to sixteen potential tipping points are now on the list.

The study finds that human emissions have already pushed Earth into the tipping points danger zone. It was released ahead of the big conference "Tipping Points: from climate crisis to positive transformation" at the University of Exeter (12–14 September). The melting of the Greenland and West Antarctic ice sheets, a widespread sudden permafrost thaw, the collapse of convection in the Labrador Sea, and a huge die-off of tropical coral reefs are five of the sixteen possible outcomes that could occur at the current temperature. At 1.5°C of global warming, four of these become likely occurrences, and five more start to have a chance of happening.

"We can see signs of destabilization 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," says lead author David Armstrong McKay of the Stockholm Resilience Centre, University of Exeter, and the Earth Commission.

"There are already some tipping points that the world could reach. More tipping moments may occur as the world's temperatures continue to rise, he warns.

"Rapidly reducing greenhouse gas emissions, starting right away, can lessen the likelihood of reaching tipping points.

The risks of causing climate tipping points increase by about 2°C over preindustrial temperatures and become very high by 2.5–4°C, according to the IPCC's Sixth Assessment Report.

According to this new estimate, when temperatures rose by more than 1°C, Earth may have already departed a "safe" climate condition. The study's conclusion is that even the United Nations' Paris Agreement objective of keeping temperature well below 2°C and ideally 1.5°C is insufficient to completely prevent severe climate change. The evaluation finds that the risk of a tipping point grows significantly in the "Paris range" of 1.5–2°C warming, with much larger risks above 2°C.

The study reveals that the risk of tipping points increases beyond the 1.5°C target, providing strong scientific backing for the Paris Agreement and related measures to keep global warming below that threshold. Global greenhouse gas emissions must be cut in half by 2030 and net-zero by 2050 in order to have a 50% chance of staying below 1.5°C and reducing tipping point dangers.                

The Potsdam Institute for Climate Impact Research director and co-author Johan Rockström asserts that "the world is headed toward 2-3°C of global warming." This puts Earth on a trajectory to pass several hazardous tipping points, which will have catastrophic effects on people all around the planet. We must make every effort to avoid reaching tipping points in order to keep the Earth habitable, safeguard people from escalating extremes, and promote stable communities. Tenths of a degree matter.

"Since I first analyzed climate tipping points in 2008, the list has grown and our evaluation of the risk they provide has increased considerably," says co-author Tim Lenton, head of the Global Systems Institute at the University of Exeter and a member of the Earth Commission.

"Our new work offers persuasive evidence that the global economy must substantially accelerate decarbonization to reduce the risk of crossing climate tipping points," the authors write.

"To do that, we must now cause favorable social tipping points that hasten the transition to a future powered by renewable energy."

Lenton continues, "We may also need to adjust to deal with climate tipping points that we are unable to prevent, and support individuals who may experience uninsurable losses and damages."

The international team came to the conclusion that 16 important biophysical systems involved in controlling Earth's climate (referred to as "tipping elements") have the potential to cross tipping points where change becomes self-sustaining after examining paleoclimate data, present observations, and climate model outputs. This means that once an ice sheet, ocean, or rainforest reaches a tipping point, it will continue to change into a new state even if the global temperature stops rising. Depending on the system, the length of the transition can range from decades to thousands of years. Ecosystems and atmospheric circulation patterns, for instance, can change swiftly, but the collapse of an ice sheet causes a slower but inescapable rise in sea level of many meters.

The tipping elements were divided into nine systems by the researchers, which include Antarctica and the Amazon rainforest, and seven other systems, which, if tilted, would have significant regional effects. The West African monsoon and the decline of the majority of coral reefs near the equator are examples of the latter. In comparison to the 2008 assessment, a number of additional tipping factors have been included, including Labrador Sea convection and East Antarctic subglacial basins, whereas the Arctic summer sea ice and the El Nio Southern Oscillation (ENSO) have been dropped due to a lack of tipping dynamics data.

Importantly, many tipping factors in the Earth system are interconnected, making cascading tipping points a critical additional worry, according to co-author and member of the Earth Commission Ricarda Winkelmann. The crucial temperature thresholds beyond which individual tipping elements start to become destabilized over time can actually be lowered through interactions.

We have taken a first step in updating the globe on tipping point threats, according to Armstrong McKay. The Earth Commission is launching the Tipping Points Model Intercomparison Project ("TIPMIP") in response to the urgent need for a deeper international analysis, particularly on tipping element interactions.

Stockholm University