A new paper has predicted that rising global temperatures will force Olympic bosses to rule out hundreds of potential host cities amid fears athletes will collapse in the heat.
The research predicts that by 2085 only 33 cities will be cool enough in summer to have competitors perform without risking heatstroke.
But – extending their model even further – scientists have predicted that by the 2100s only Edinburgh, Glasgow, Belfast and Dublin will be capable of hosting the games.
The severely reduced set of potential host cities would put Scotland on the cards to host once every eight years – with Ireland and Northern Ireland sharing the rest of the glory.
The paper – from the University of California, Berkeley’s School of Public Health – is titled “The last Summer Olympics? Climate change, health and work outdoors”.
To narrow down host cities, lead-author Kirk Smith first ruled out smaller ones which lack infrastructure and those with too high an altitude, which could cause performance issues.
The paper also only examines cities in the northern hemisphere – which currently contains nearly 90% of the world’s population.
To measure safety Mr Smith and his team used the marathon, which he says “is the most demanding endurance event, and thus provides a fair indication of whether conditions are likely to be safe for any other Olympic event.”
Using the wet-bulb globe temperature (WGBT) scale – which measures heat, humidity and wind speed – they determined that 26° was the maximum allowable temperature for the race to go ahead.
Any temperature above 26° is deemed medium to high risk to the health of runners – who could collapse from heatstroke, dehydration or exhaustion.
For comparison, he notes: “In 2016, only about 70% of the elite competitors in the US Olympic Team Trials Marathon in Los Angeles finished, in a race where peak temperature reached 25.6°.”
They then used climate change models to predict the temperature of host cities by 2085 in the summer months of July and August, when the games traditionally take place.
Using models which predict a rise in temperature owing to greenhouse gases they found only 33 cities with a less than 10% chance of having to cancel the marathon owing to heat above 26°.
Mr Smith notes: “We assumed that any venue with more than a 10% chance of having the cancel the marathon at the last minute owing to exceedance of the safe WBGT limit would not be a viable choice to hold the Games as they are structured today.
“A 10% criterion has previously been used to judge venues for the Winter Olympics in terms of prospects for cold nights and sufficient snow.”
Of the 33 viable cities in 2085 15 are in the UK.
They are London, Coventry, Birmingham, Nottingham, Leicester, Southampton, Bristol, Sheffield, Manchester, Liverpool, Leeds, Newcastle, Belfast, Edinburgh and Glasgow.
Outside the UK many of the other viable cities are in Western Europe, including Malmo, Copenhagen and Oslo.
Only three North American cities make the cut – San Francisco, Calgary and Vancouver – along with the two Asian cities of Bishkek in Kyrgyzstan and Ulaanbaatar in Mongolia.
Three Eastern European cities are also declared safe – St Petersburg and Krasnoyarsk in Russia and Riga in Latvia – whilst Africa and Latin America are completely ruled out.
But, the study goes on: “Projections out to the early 22nd century, which carry even more uncertainty, suggest the last cities in the northern hemisphere with low-risk summer conditions for the games will be Belfast, Dublin, Edinburgh and Glasgow.”
The research has come to light just two days after British triathlete Jonny Brownlee collapsed in temperatures of 33° in a World Triathlon Series event in Mexico.
His brother Alistair carried him across the finish line, helping him secure second place in the event.