Climate tipping points: How close are we to irreversible change?

The planet is edging far closer to irreversible change than most policy debates acknowledge, according to the most comprehensive probability analysis yet of climate “tipping points.”

The research was a collaboration between the University of Exeter’s Global Systems Institute and the University of Hamburg.

The experts have calculated that, if governments follow their present course, there is roughly a two-in-three likelihood that at least one major Earth-system component will tip into a radically different and largely irreversible state.

Tipping points measured in the study

Tipping points are thresholds where small incremental warming forces a system – such as an ice sheet, an ocean circulation pattern, or a vast forest – into a self-propagating transition. To gauge just how close humanity is to those thresholds, lead author Jakob Deutloff and colleagues looked at sixteen well-studied tipping elements.

Their list included collapse of the West Antarctic and Greenland ice sheets, disruption of the Atlantic Meridional Overturning Circulation, wholesale die-off of the Amazon rainforest, abrupt thaw of Arctic permafrost, and several others ranging from coral reefs to boreal forests.

Using the Finite-amplitude Impulse Response (FaIR) climate model coupled to a simplified representation of Amazon dieback and permafrost thaw, the team ran tens of thousands of Monte-Carlo simulations.

These runs sampled three layers of uncertainty: the planet’s sensitivity to greenhouse gases, the temperature thresholds at which each element could tip, and the time each system would take to complete its transition.

Are the tipping points avoidable?

The researchers then drove the model with five standard emissions pathways, known as Shared Socioeconomic Pathways (SSPs). The scenario that best matches today’s national policies – SSP2-4.5, which delivers about 2.8 °C of warming by 2100 – proved alarmingly unsafe.

Averaged across all sixteen tipping elements, the probability of at least one being triggered reached 62 percent. Nine of the elements exceeded 50 percent likelihood individually, including the West Antarctic Ice Sheet, the Greenland Ice Sheet and the Amazon rainforest.

Under higher-emission futures such as SSP3-7.0 or SSP5-8.5, tipping virtually becomes unavoidable for most elements.

Conversely, more aggressive mitigation plans that align with the Paris Agreement – SSP1-2.6 (about 1.8 °C peak warming) and SSP1-1.9 (1.5 °C) – cut the average probability to roughly 37 percent and 14 percent, respectively, though they do not eliminate risk entirely.

Extra push from carbon-cycle feedbacks

The study also tackled a longstanding concern that emissions released by one tipping element – specifically Amazon dieback or permafrost thaw – could generate sufficient extra warming to push others over the edge.

By embedding a conceptual carbon-feedback module inside FaIR, the researchers found that even under current-policy warming, additional carbon from those two sources would raise global temperature by a median of only 0.22 °C by 2300.

That figure is an order of magnitude smaller than the warming driven directly by human activity and increases the average tipping probability by just three percentage points. In high-emission futures the absolute carbon release is larger, but the boost to global temperature is proportionally smaller because anthropogenic emissions dominate.

The conclusion: feedbacks from these two carbon-rich systems are not, on their own, likely to set off a domino cascade. Nonetheless, the authors caution that other physical interactions – such as changes in ocean circulation or cloud cover – could still amplify risks in ways not captured by the present model.

Global warming: A question of timing

One of the biggest unknowns remains how fast each tipping element responds once its threshold temperature is crossed. The team calculated two extremes.

In an “instantaneous” view, an element flips as soon as the global mean temperature passes its threshold. In an “equilibrium” view, tipping occurs only if temperature remains above that threshold after the climate stabilizes.

For high-emission scenarios, where warming climbs continuously, the distinction hardly matters. In mitigation pathways that involve a mid-century overshoot followed by cooling, however, the assumed reaction speed makes a dramatic difference: instantaneous triggering can more than double the probability relative to the equilibrium calculation.

Preventing the climate tipping points

“The good news from our study is that the power to prevent climate tipping points is still in our hands,” Deutloff said.

“By moving towards a more sustainable future with lower emissions, the risk of triggering these tipping points is significantly reduced. And it appears that breaching tipping points within the Amazon and the permafrost region should not necessarily trigger others.”

Study co-author Tim Lenton warmer that climate tipping points could have devastating consequences for humanity,. “It is clear that we are currently on a dangerous trajectory – with tipping points likely to be triggered unless we change course rapidly.”

“We need urgent global action – including the triggering of ‘positive tipping points’ in our societies and economies – to reach a safe and sustainable future,” said Lenton.

Rapid transitions are urgently needed

Positive tipping points refer to self-reinforcing social and technological shifts – such as rapid adoption of renewable energy, electric vehicles or new food systems – that can drive emissions downward at exponential rates.

The authors argue that deliberately engineering such rapid transitions is now humanity’s best chance of keeping global warming below levels where probabilities of catastrophic change climb toward certainty.

The numbers in the study translate an abstract worry into a concrete risk metric: a 62 percent chance of rolling the dice on irreversible change under today’s national pledges.

Whether that gamble is acceptable, they say, will be decided by the policy choices of this decade, choices that will echo for centuries through the stability of ice sheets, forests, ocean currents – and the societies that depend on them.

The study is published in the journal Earth Systems Dynamics.

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