Heatwaves were the deadliest climate disasters in 2025, hitting poorest hardest, WWA finds

While climate change fuelled a year of devastating extreme weather across the world in 2025, heatwaves — often described as “silent killers” — were the deadliest climate-related disasters, disproportionately affecting poor and marginalised communities, according to a new annual report by World Weather Attribution (WWA).

Although 2025 did not surpass the global temperature record set in 2024, it will rank among the hottest years ever recorded, exposing how continued fossil fuel use is pushing societies closer to the limits of adaptation. Crucially, for the first time in history, the three-year global average temperature crossed the 1.5 degrees Celsius (°C) threshold.

Scientists said this milestone marked a dangerous shift, as even years influenced by cooler natural climate cycles are now delivering extreme heat with devastating consequences. “Being the second or third hottest year on record is not good news,” the report noted.

Heatwaves the deadliest extreme

WWA identified 157 extreme weather events in 2025 that met its humanitarian impact criteria. Floods and heatwaves were the most frequent, with 49 events each, followed by storms, wildfires and droughts. Of the 22 events studied in depth, 17 were found to have been made more severe or more likely by climate change.

In addition, six major heatwaves from previous years were revisited to assess how risks have evolved since the Paris Agreement was adopted.