By 2085 it will be too hot for most big cities in the northern hemisphere to host the Olympic Games, according to a new study.
The research, led by the University of Auckland, has been published in the British medical journal The Lancet. It looked at the effects of rising temperatures on the safety of athletes running marathons in summer.
The study found that 69 years from now, only a handful of cities will be in the low-risk category for hosting the Games: three in North America, two in Asia and none in Africa.
Projections to early next century suggest the remaining cities with low-risk summer conditions will be Belfast, Dublin, Edinburgh and Glasgow.
Study co-author Alistair Woodward said increasing restrictions on when, where, and how the Games could be held due to extreme heat signals were a problem - as were the implications for everyone else.
"If the world's most elite athletes need to be protected from climate change, what about the rest of us?" he said.
Professor Woodward said the world beyond 2050 poses difficult challenges, including figuring out how to balance the extent and speed of change with society's ability to adapt to it.
The study was carried out in collaboration with the University of California, the Nelson Marlborough Institute of Technology, and the Centre for Technology Research and Innovation in Cyprus.
Prof Woodward said the risk of so-called "pernicious impacts" - those requiring trade-offs between what society generally assumes and values and what is healthy - would rise.
He said the most detrimental impact could be the broadening of places and seasons in which heavy work was no longer safe either outdoors, or even in unprotected indoor spaces.
"As more than half the planet's workforce works outdoors, primarily in construction and agriculture, society faces an increasingly serious trade-off between population health and labour productivity," he said. "The risk to workers' health could be minimised if workers are allowed to sit in the shade during the hottest times of day and take breaks during hot, humid months."
Otherwise, people who work outside will be increasingly at risk from exertional heat stroke - which can be fatal.
Prof Woodward said heavy outdoor work was already limited in some parts of the world by heat stress, but climate change meant more regions would be affected for a greater part of the year.