“One player gonna die,” complained Daniil Medvedev in the middle of a match on the hottest day of the US Open in New York last year, as the temperature soared to 34°C. “It’s been brutal…it ruins everything.” Similar temperatures—combined with higher humidity—sometimes made conditions even more punishing at this year’s tournament that ended on September 8th. Players struggled and vomited; in the breaks they packed bags of ice around their necks and heads, or stuck hoses blowing cold air down their shirts in an effort to cool down. Sweltering in the steeply sloping cheaper seats was the largest crowd ever: in all, some 1m spectators attended the competition, fulfilling a goal the organisers had set in 2019.

Since the turn of the 20th century, shortly after a version of the US Open first began, the average summer in New York has warmed by around 2°C. Annual average temperatures globally have risen by roughly half that. An even starker trend was evident at the Olympic games in Paris earlier this year. In the 100 years since the games had last been held there in 1924, the average temperature in the city in August has risen by 2.7°C.

Climate change means that places once deemed perfect for large sports events are starting to seem unsuitable. At the same time, the size and value of such events have grown, as has the demand to hold them in a wider range of locations. The collision of both trends has made international sports competitions more difficult and dangerous, and left hosts increasingly reliant on elaborate workarounds.

Many sports are sensitive to the environment in which they are played. Some obviously require specific conditions, such as snow for skiing and wind for sailing (or a lack of rain for cricket). Changing weather patterns, as well as higher temperatures, are limiting where those fixtures can be held, at least without technological intervention. The Winter Olympics in Beijing in 2022 were the first to be held on entirely artificial snow. They won’t be the last: a study published in 2022 found that even if the rise in global temperatures is limited to 1.5°C above pre-industrial levels—which is now all but impossible—only 13 of the 21 places that previously hosted the Winter Olympics would be able to do so by 2050.

Beyond sweeping planetary changes, seemingly small variations in temperature make a huge difference to athletes’ performance. The sapping effect of warm weather is well known, and is why they often try to acclimatise themselves before competitions in hot places. Even then, though, only so much adaptation is possible: higher temperatures hasten dehydration, cause glucose to be broken down more quickly and reduce the amount of oxygen sent to the muscles (the body has to prioritise sending blood to the skin in order to cool itself down).

The cumulative effect of too much heat is seen most clearly during endurance events—and it can be dramatic. A study of more than 100 athletes competing in long-distance races at the 2019 World Athletics championship—held in hot, muggy Qatar—found that virtually all did 3-20% worse than their personal best, with performance falling alongside rising wet-bulb globe temperatures (a measure of heat, humidity and solar radiation that best reflects the impacts on a human body). This was despite the organisers taking some extreme measures: all track and field events were held in a vast air-conditioned stadium, and the road races had to be run in the middle of the night.

Warmer weather can act as a drag in less obvious ways, too. Heat stress is known to harm decision-making and motor skills. A growing body of evidence suggests that it may make athletes across many sports more clumsy or quarrelsome.

Most professional sportsmen and women seem to be aware of such effects: three-quarters of respondents to a survey published by the World Athletics Association said that climate change had a direct negative impact on their health and performance. The physical consequences of competing in hot weather can range from cramp and dizziness to sudden death. Exertional heat stroke (EHS) occurs when a body overheats during strenuous activity and can lead to seizures and organ failure. The mortality rate for people hospitalised with EHS hovers around 15%; untreated it may be 80%. The condition is thought to be the third-leading cause of sudden death among young American athletes.

Playing it cool

Global warming means that organisers of competitions must now work harder to keep athletes safe. The first step is understanding when conditions are simply too dangerous. In recent years international federations have begun introducing extreme-heat policies, which prescribe measures like additional breaks or postponements once temperature thresholds are crossed. Most policies, though, fail to factor in the physical stress experienced by athletes already pushing themselves to their limits. The United States Tennis Association, for example, suspends play or closes the sliding roof at the US Open only when the wet-bulb globe temperature reaches 32.5°C, even though the American College of Sports Medicine recommends that outdoor events be limited or cancelled when this measure goes above 28°C.

Once adequate safety measures are decided on, implementing them requires careful contingency planning, so that timings and locations can be reshuffled if necessary. To help with this, a new industry has sprung up to supply organisers with bespoke weather forecasts. For example, a private division of Météo France, the French national weather agency, has specialised in sports forecasts for the past two decades. At this year’s Olympics in Paris, the modelling it provided was so detailed that it included how the perceived temperature in the Grand Palais—an exhibition hall used as the venue for fencing and taekwondo—would change according to the angle of the sun hitting the building’s vaulted glass roof. Demand for such services has increased, says Alexis Decalonne, who leads the unit. Its clients include Formula One motor races across Europe and the Wimbledon tennis tournament.

Organisers must also mitigate the risks that heat poses for spectators. Some protective measures can be put in place in advance, such as making sure that enough shade and water are available throughout the areas that crowds will move through. Ahead of the Paris Olympics, for example, some 300,000 trees were planted around the city. In addition, hundreds of new drinking fountains were installed and venues’ security rules were altered to allow spectators to bring in reusable water bottles (a change so drastic that it required the French prime minister’s approval).

Yet, in some cases, improving safety conflicts with commercial needs, as the most popular sporting events grow in size and value. Gargantuan tournaments are already regular fixtures in all types of sports, from handball and gymnastics to motor racing—and they keep getting bigger.

Between 1964 and 2018 the collective size of the summer or winter Olympics and men’s football World Cups—as indicated by the number of athletes, ticket revenue, sponsorship revenue, media coverage and the costs of hosting—rose roughly 60-fold, according to researchers at the University of Lausanne.

Most big events lose money, but potential hosts often seem to care more about bolstering their own image. A growing number of new countries are increasingly keen to host big events, even if their climates are not appropriate. To hold the FIFA football World Cup in Qatar in 2022, organisers shifted the tournament’s timing from the summer to the winter, and installed air-conditioning throughout outdoor stadiums. Saudi Arabia won its bid to hold the 2029 Asian Winter games in the middle of the desert by promising to build 36km of artificial ski slopes in NEOM, a futuristic city that doesn’t yet exist. India’s bid for the 2036 Summer Olympics seems impossible without huge amounts of technological innovation or the host being allowed to schedule it later in the year.

Some of the extreme measures taken to hold events in places too hot for them exacerbate the sports industry’s own environmental sins, which are already substantial. Organisers of the 2022 football World Cup claim it was responsible for the emission of about 3.6m tonnes of carbon dioxide, or roughly the same amount as in the 2016 Olympics in Rio de Janeiro. (Independent estimates of emissions from the Qatar World Cup were strikingly higher.)

Making the biggest sporting events greener is possible, if tricky. The organisers of the Paris Olympics, for example, promised to halve their emissions compared with their most recent rivals (ignoring the Tokyo games, which were held during a covid-19 lockdown). They seem to have succeeded, after serious effort. According to Georgina Grenon, the Olympics’ sustainability director, the organisers had to rethink everything from which back-up generators broadcasters would use, to what proportion of food ingredients should come from France to reduce the amount flown in. Steps they took to reduce waste included renting rather than buying some of the 600,000 pieces of furniture that were needed.

Such efforts are not to be sniffed at. But organisers also had to rely heavily on carbon offsets, highlighting the difficulties in cleaning up a model built around pulling ever-larger numbers of fans and competitors from around the world.

The question, then, is whether that model can remain viable as the mercury keeps rising. “These poor guys…it is not humane,” concluded John McEnroe, a tennis champion-turned-commentator after watching Mr Medvedev’s quarter-final game against Andrey Rublev at the US Open last year. He went on to complain that the heat had turned the tournament into “a war of attrition”. He could have been talking about many of sport’s most famous fixtures.