World capitals are enduring far more dangerously hot days than in the 1990s, a new study shows.

Research by the International Institute for Environment and Development (IIED) found that across 43 major cities, the number of days above 35 °C has risen by 25% in three decades. Annual totals jumped from about 1,062 hot days in the 1990s to 1,335 in the past decade, peaking at 1,612 in 2024.

Some cities are seeing dramatic surges: Madrid now averages 47 scorching days a year, nearly double its 1990s count. Rome and Beijing have also doubled, while Manila has tripled. Even cooler capitals like London have seen the number of days above 30 °C double.

Experts warn that climate change, worsened by fossil fuel emissions and urban heat island effects, is putting millions at risk. They urge rapid action: more green spaces, better housing design, and stronger heat-response plans alongside urgent cuts in global emissions.