Could the climate pass a point of no return?

Possibly. A tipping point is a threshold that, once crossed, reorganises a system, often for good. The new state may not return to the old one even if the push that caused it is reversed. Physicists call this kind of memory hysteresis. A magnet shows it: it can keep pointing one way after the field that set it is gone.

As of 2022, scientists listed nine global and seven regional tipping elements in the climate. Four are judged likely to tip if warming reaches 1.5 °C: the Greenland and West Antarctic ice sheets, tropical coral reefs, and the sudden thaw of northern permafrost.

Tipping is not always fast. Greenland's ice sheet could pass its tipping point somewhere between 0.8 and 3 °C of warming. But the melting itself would then take millennia.

The Amazon is a closely watched case. A 2020 study found about 40 percent of the forest at risk of turning into something like savanna, as rainfall drops. In a normal year, the Amazon absorbs about 1.5 billion tonnes of carbon dioxide. In the droughts of 2005 and 2010, it released 5 and then 8 billion tonnes instead.

Scientists also worry about cascades, where one tipping point helps trigger another. Melting ice sheets would change ocean circulation, which could in turn push permafrost and northern forests toward their own thresholds.

Views have shifted fast. In the early 2000s, the IPCC thought tipping points were likely only at 4 °C of warming or more. By 2021, some were considered possible at today's warming of just over 1 °C, and highly probable above 2 °C. The British scientist Timothy Lenton, called a leading tipping point expert, was honoured in 2025 for his work on these thresholds.