Climate change is set to make it too hot to host the Olympics in the world's biggest cities, according to a university study.
The University of Auckland has undertaken research which has found about 90 per cent of the Northern Hemisphere's most populous cities will become too hot and humid over the next 70 years to safely hold the Games.
Professor Alistair Woodward said the study focused on whether cities in the Northern Hemisphere would be able to stage the marathon without posing a significant risk to athletes.
"Only three cities in North America, two in Asia and none in Africa will fall in the low risk category," he said.
"Projections suggest the last cities with low-risk summer conditions will be Belfast, Dublin, Edinburgh and Glasgow.
"Increasing restrictions on when, where, and how the Games can be held owing to extreme heat are a sign of a much bigger problem," Woodward said.
"If the world's most elite athletes need to be protected from climate change, what about the rest of us?"
The study has been published in British medical journal The Lancet this week, and was undertaken in collaboration with the University of California, the Nelson Marlborough Institute of Technology, and the Centre for Technology Research and Innovation, at Limassol in Cyprus.