By 2085, only eight Northern Hemisphere cities outside of western Europe are likely to be cool enough to host the summer Olympic games, predict researchers. San Francisco would be one of just three North American cities that could serve as hosts, they say.

The commentary, published in The Lancet, comes from a larger study about climate change.

Its authors explain how their findings can be used to examine the viability of future Olympics sites based on a measurement that combines temperature, humidity, heat radiation, and wind—their wetbulb globe temperature (WBGT). Researchers used two climate models to project rising temperatures over the next century and applied those results to current safety procedures used in determining the viability of a host city.

The final study, which is still forthcoming and holds much broader implications than the future of outdoor Olympics, examines the relationship between health and productivity as the global climate continues to warm. The opening ceremonies of the 2016 games in Rio, however, did acknowledge climate change, and the impact that rising temperatures could have on the future of the games was not lost on the researchers.

“Climate change could constrain the Olympics going forward,” says Kirk Smith, a professor of global environmental health at the University of California, Berkeley, School of Public Health. “And not just because of rising sea levels.”

Canceled marathons

The findings focus on the Northern Hemisphere, home to 90 percent of the world’s population. The authors considered only cities with at least 600,000 residents, the size considered necessary for hosting the games. Cities with elevations over a mile above sea level were omitted, as the most recent Olympic games hosted at such an altitude (Mexico City in 1968) faced challenges of their own.

The findings assumed that any venue with more than a 10 percent chance of having to cancel a marathon—one of the summer Olympics’ signature and exclusively outdoor events—on short notice would not be a viable host city.

“If you’re going to be spending billions of dollars to host an event, you’re going to want have a level of certainty that you’re not going to have to cancel it at the last minute,” Smith says.

The 10 percent criterion is currently used to evaluate potential sites of the winter games. If a potential host city is too unlikely to produce enough snow or cold enough temperatures, the chances of its bid winning decreases.

Suitable sites

The findings indicate that by 2085, Istanbul, Madrid, Rome, Paris, and Budapest—all cities that are or were in contention for either the 2020 or 2024 Summer Olympics—would be unfit to host the games. Tokyo, the city that has secured the 2020 summer Olympiad, would also be too hot to ensure athlete safety, should these projections come to pass.

According to the findings, among the 8 out of 543 cities outside of western Europe would qualify as “low-risk” sites, including St. Petersburg, Russia; Riga, Latvia; Bishkek, Kyrgyzstan; and Ulaanbaatar, Mongolia.

In North America, Calgary, and Vancouver would join San Francisco as the only three suitable sites. Both Canadian cities have hosted Olympics before—but the winter games, Calgary in 1988 and Vancouver in 2010. San Francisco explored the possibility of hosting this year’s summer games, but ultimately withdrew the bid in 2006.

Latin America and Africa combined would fail to provide a single viable city.

Western Europe is home to 25 cities that would be “low-risk” sites in 2085, according to the calculations.

But by the 22nd century, if their projections play out, the scientists concluded only four Northern Hemisphere cities would be left on the list: Belfast and Dublin, Ireland; and Edinburgh and Glasgow in Scotland.

Move the whole thing indoors?

While these findings are concerned with the more distant future, being able to ensure athlete safety in the face of spiking temperatures is already an issue in outdoor summer competitions. In October 2007, the Chicago Marathon was canceled mid-race as hundreds of runners succumbed to the heat and sought medical attention. High temperatures also wreaked havoc this year during the US Olympic Team trials marathon in Los Angeles, where 30 percent of the Olympic hopefuls failed to finish as the temperature on race day pushed 80 degrees Fahrenheit.

Should the findings reported in this commentary bear out, obvious work-arounds exist, such as running the Olympics indoors entirely or eliminating heat-sensitive endurance events like the marathon. Both solutions, however, would require a dramatic reimagining of how the modern Olympics are constructed.

“Climate change is going to force us to change our behavior from the way things have always been done,” says Smith. “This includes sending your kids outside to play soccer or going out for a jog. It is a substantially changing world.”

Alistair Woodward of the University of Auckland, who coauthored the commentary, echoed Smith’s sentiments in a press release following the publication of the findings, saying, “If the world’s most elite athletes need to be protected from climate change, what about the rest of us?”

John Balmes of UC Berkeley is another coauthor of the commentary.

This post originally appeared on Futurity and is reprinted under Creative Commons.

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