A climate tipping point is a threshold beyond which self-sustaining processes irreversibly push a part of Earth's climate system from one state into another. The concept was formalised roughly two decades ago. Scientists reckon they have arrived at a decent understanding of which parts of the system are most vulnerable to tipping, though the exact warming thresholds remain uncertain.
Amazon dieback. The Amazon rainforest is so large that it makes its own climate: its billions of trees produce enough moisture to form clouds responsible for at least a third of the forest's rainfall. Climate change raises temperatures, worsens droughts and increases fires, all of which kill trees. Fewer trees mean less rainfall, higher temperatures and more fires, creating a self-perpetuating cycle. If the forest shrinks beyond a critical point, much of the basin would turn into dry savannah, releasing tens of billions of tonnes of stored carbon dioxide. Models put the irreversible threshold somewhere between 2°C and 6°C of warming, though deforestation by humans could bring it sooner. Reducing deforestation may therefore help defer the tipping point.
Greenland ice sheet. The breakdown of the vast Greenland ice sheet would raise global sea levels by more than seven metres. Models disagree on the threshold: some suggest irreversible decline could begin at 0.8°C above pre-industrial levels (roughly the turn of the millennium), others at closer to 3°C. Fresh water from a collapsing ice sheet would weaken the AMOC, further reducing rainfall over the Amazon—an example of how one tipping point can trigger another, domino-style.
AMOC collapse. The collapse of the Atlantic Meridional Overturning Circulation would cause dramatic falls in temperature and rainfall across Europe, greatly damaging the continent's ability to grow crops.
In February 2025 ARIA announced an initial five-year, £81m ($109m) programme to fund systems producing and processing the data needed for an "early warning system for tipping points". The programme involves 26 teams focusing on two tipping points: the breakdown of the Greenland ice sheet and the collapse of the subpolar gyre, a circulating current in the north Atlantic that helps power AMOC. If too much fresh water from melting ice flows into the gyre, it could be disrupted, increasing the odds of an AMOC collapse.
Among the teams, Kelly Hogan of the British Antarctic Survey plans to use a fleet of small underwater drones to map the ice face and measure salinity, temperature and current force. Oshen, a British startup, intends to deploy small, self-sailing robots with solar-powered sensors in the subpolar gyre. Marble, another British company, is developing drones that can monitor iceberg positions, glacier-front location and the height of the Greenland ice sheet. Tim Lenton of the University of Exeter, a pioneer of tipping-point research, leads one of the teams working out how data might inform an early-warning system.
Both Oshen and Marble say their work is only possible because smartphone technology has made sensors and processing power cheap, and widespread 4G coverage allows rapid data transfer.
Earth's climate is governed by myriad interconnected processes. The dynamics of ice-sheet disintegration and cloud formation, for instance, are only poorly understood. Cloud formation occurs at scales too small to be properly incorporated into planetary models. Different models therefore rely on different approximations, producing wide-ranging projections.
An example of an imperfectly understood effect: boreal wildfires, which have grown considerably larger since the early 2010s, produce smoke whose brighter, more reflective particles may cool the ground below. One analysis suggests this negative feedback could delay an ice-free Arctic September from 2050 by over a decade, and maintain Arctic sea-ice extent at least 3m square kilometres more than fire-trend-free models project for the 2030s. But fires also release carbon that warms the planet over time.
As of 2025, no government is considering scenarios like ice-sheet collapse with the seriousness afforded to other high-impact risks such as pandemics, with the possible exception of the Nordic countries. COP30, the 2025 UN climate summit, is expected to place particular emphasis on tipping points; it is being held in Belém, a Brazilian city dubbed "the gateway to the Amazon".
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