Most cities might be too hot to host the summer Olympic Games after 2085 because of climate change, according to an analysis in The Lancet1.Using climate modelling and a measure of heat stress to the human body, researchers led by Kirk Smith, an environmental-health researcher at the University of California, Berkeley, judged whether cities would be suitable for hosting the Games.The authors used a measure known as the wet-bulb globe temperature, which takes into account how factors including temperature, humidity and wind speed affect people, especially during exercise. They used climate models under a high-emissions scenario to predict what this measurement would be for various cities in the future.

The team proposed that it would be low risk to run a marathon if the wet-bulb globe temperature is less than 26 °C in the shade. Any location that had a more than 10% chance of having higher temperatures for the marathon would not be a viable host city.

The study looked only at cities in the Northern Hemisphere — home to 90% of the world’s population, and where summer occurs in July and August — and excluded those at an altitude of more than 1,600 metres (altitude had been a problem at the 1968 Mexico Olympics), as well as cities with populations of less than 600,000.That left 25 suitable cities in western Europe for the 2088 Games — more than half of which are in the United Kingdom — and just 8 in the rest of the Northern Hemisphere, including San Francisco in California, St Petersburg in Russia and Ulaanbaatar in Mongolia.

Credit: Source: K. R. Smith et al. Lancet 388, 642–644 (2016).

And according to the researchers' calculations, none of the cities that bid for the 2020 summer Games — Tokyo, Madrid and Istanbul — would be fit to be a host.