Hot cities: researching extreme heat in the world's biggest capital cities

We have analysed rising temperatures in 43 of the world’s major cities, home to a total of nearly 470 million people.

Our research found a 26% rise in the average number of days reaching 35°C every year over the last three decades.

Those cities – the 40 largest capitals plus three more politically significant cities – experienced an average total of 1,062 of these very hot days per year between 1994 and 2003. As of 2024, that has leapt to 1,335.

Some places, such as Kuala Lumpur and Rome, have seen their averages more than double in that time.

Heat is one of the effects of climate change that doesn’t discriminate: whether you live in London or Luanda, it’s a potentially deadly problem that will only get worse.

This ‘hot cities’ research, which is an expanded version of work from 2024 looking at the 20 biggest capitals, highlights the urgent need for policymakers to help communities adapt to the new reality of hotter temperatures.

The research also aims to raise the mainstream media profile of the impacts of climate change; showing concrete examples of how people, health, services, infrastructure and livelihoods in cities in the global North and South are suffering from extreme heat – a consequence of inaction on climate change.

Detailed analysis of the research (PDF), as well as the full data for each of the cities for above 30°C and 35°C, is available to download.