World’s major cities hit by 25% surge in extreme heat since 1990s

The world's major capitals are facing 25% more extremely hot days each year compared to the 1990s, a new analysis warns. 

Without swift action, millions of urban residents will increasingly suffer under dangerous temperatures, reports The Guardian, citing experts.

From Washington DC and Madrid to Tokyo and Beijing, the International Institute for Environment and Development (IIED) found a sharp rise in days above 35°C. 

Across 43 of the most populous capitals, the annual average jumped from 1,062 in 1994-2003 to 1,335 in 2015-2024.

The increase is global with the number of scorching days doubled in Rome and Beijing, tripled in Manila, and nearly doubled in Madrid, where residents now endure 47 days above 35°C each year, compared to 25 before. Even London, traditionally temperate, has seen its 30°C days double.

Scientists attribute the surge to global heating driven by fossil fuel use, which amplifies every heatwave. Over the past three decades, extreme heat has likely caused millions of premature deaths, disproportionately affecting the elderly and poor in rapidly growing cities.

"Global temperatures are rising faster than governments probably expected and definitely faster than they seem to be reacting," said Anna Walnycki, an IIED researcher. "Failing to adapt will condemn millions of city dwellers to increasingly uncomfortable and even dangerous conditions because of the urban heat island effect."

"The poorest people will likely suffer the most whether they're in London, Luanda or Lima, but the impacts will be significantly worse in low-income or unplanned communities in the global south thanks to lower-quality housing," she said, noting that a third of the world's city dwellers live in slums or informal settlements. "Climate change is the new reality. Governments can't keep their heads buried in the sand any more."

The new analysis compiled temperature data for the 40 most populous capital cities and three further cities with high political significance this year. The UN's climate summit, Cop30, will be held in Brazil in November and its capital, Brasília had only three days over 35°C in total between 1994 and 2003, compared with 40 between 2015 and 2024. In South Africa, which holds the current G20 presidency, residents of Pretoria now have 11 days a year over 35°C on average, up from only three a year in the 1990s.