As the planet warms, it risks crossing catastrophic tipping points: thresholds where Earth systems, such as ice sheets and rain forests, change irreversibly over human lifetimes. Scientists have long warned that if global temperatures warmed more than 1.5 degrees Celsius compared with before the Industrial Revolution, and stayed high, they would increase the risk of passing multiple tipping points. With these warnings in mind, 194 countries a decade ago set 1.5 C as a goal they would try not to cross. Yet in 2024, the planet temporarily breached that threshold.
A tipping point is a metaphor for runaway change. Small changes can push a system out of balance. Once past a threshold, the changes reinforce themselves, amplifying until the system transforms into something new. The scientific reality of tipping points is more complicated than crossing a temperature line. Instead, different elements in the climate system have risks of tipping that increase with each fraction of a degree of warming. Climate scientist Timothy Lenton first identified climate tipping points in 2008. In 2022, he and his team revisited temperature collapse ranges, integrating over a decade of additional data and more sophisticated computer models.
For example, the beginning of a slow collapse of the Greenland ice sheet, which could raise global sea level by about 24 feet (7.4 meters), is one of the most likely tipping elements in a world more than 1.5 C warmer than preindustrial times. Some models place the critical threshold at 1.6 C (2.9 F). More recent simulations estimate runaway conditions at 2.7 C (4.9 F) of warming.
In the Amazon, self-perpetuating feedback loops threaten the stability of the Earth’s largest rain forest, an ecosystem that influences global climate. As temperatures rise, drought and wildfire activity increase, killing trees and releasing more carbon into the atmosphere, which in turn makes the forest hotter and drier still. By 2050, scientists warn, nearly half of the Amazon rain forest could face multiple stressors. That pressure may trigger a tipping point with mass tree die-offs. The once-damp rain forest canopy could shift to a dry savanna for at least several centuries.
Not all scientists agree that an AMOC or rain forest collapse is close. Despite the uncertainty, tipping points are too risky to ignore. Rising temperatures put people and economies around the world at greater risk of dangerous conditions. But there is still room for preventive actions – every fraction of a degree in warming that humans prevent reduces the risk of runaway climate conditions. Reducing greenhouse gas emissions slows warming and tipping point risks. Tipping points highlight the stakes, but they also underscore the climate choices humanity can still make to stop the damage.
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