Extreme heat is pushing global agrifood systems to the brink, threatening the livelihoods and health of more than a billion people, according to a new report by the UN's food and weather agencies.

The United Nations Food and Agriculture Organization (FAO) and the World Meteorological Organization (WMO) said heatwaves are becoming more frequent, intense and prolonged, damaging crops, livestock, fisheries and forests.

"Extreme heat is rewriting the script on what farmers, fishers and foresters can grow and when they can grow. In some cases it is even dictating if they can still work," said Kaveh Zahedi, head of FAO's climate change office.

"At its core, this report is telling us that we face a very uncertain future," he told Reuters.

Recent climate datasets show global warming is accelerating, with 2025 ranking among the three hottest years on record, triggering more frequent and severe weather extremes.

Acting as a risk multiplier, extreme heat intensifies droughts, wildfires and pest outbreaks and sharply cuts crop yields once critical temperature thresholds are breached.

RISKS ESCALATE RAPIDLY AS TEMPERATURES PUSH HIGHER
The report said higher temperatures are shrinking the safety margin that plants, animals and humans rely on to function, with yields for most major crops falling once temperatures exceed about 30 °C.

Zahedi cited Morocco, where six years of drought were followed by record heatwaves. "This led to a fall in cereal yields by over 40%. It decimated the olive and citrus harvest. Basically, those harvests failed," he said.

Marine heatwaves are also becoming more frequent, depleting oxygen levels in water and threatening fish stocks. In 2024, 91% of the world's oceans experienced at least one marine heatwave, the report said.

Risks rise sharply as warming accelerates. The intensity of extreme heat events is expected to roughly double at 2 °C of warming and quadruple at 3 °C, compared with 1.5 °C, the report said.

Zahedi said every 1 °C rise in average global temperatures cuts yields of the world's four major crops - maize, rice, soya, and wheat - by about 6%.

The FAO and WMO said piecemeal responses were inadequate and called for better risk governance and early-warning weather systems to help farmers and fishers take preventive action.

"If you can get the data into the farmers' hands, they can adjust when they plant, they can adjust what they plant, they can adjust when they harvest," Zahedi said.

But the report said adaptation alone is not enough, arguing the only lasting solution to the growing threat of extreme heat is ambitious, coordinated action to curb climate change.