Athletes are raising concerns about how extreme heat might affect the Summer Olympic Games in Paris, according to a new report. They’re worried that soaring temperatures pose serious health risks to competitors and spectators, not to mention their performance suffering.

Average temperatures during the months when the Summer Olympics are typically held have risen by more than 3 degrees Celsius (5.4 degrees Fahrenheit) since the last time the Games were held in Paris in 1924, according to the report. Every fraction of a degree of difference can have an impact, considering even a 0.5 degree Celsius rise in core body temperature can increase a person’s heartbeat up to 10 beats per minute. In a worst-case scenario, that can lead to heat exhaustion that could worsen into heatstroke without any intervention.

Summers are getting hotter with climate change, setting the stage for riskier outdoor competitions. That means there needs to be more action taken to protect athletes and their fans, advocates say, especially with the upcoming Games in Paris expected to be a scorcher.

“At the very least, heat impacts place athletes under a competitive disadvantage, disrupting sleep and forcing them to train earlier and earlier into the morning just to avoid the worst temperatures of the day,” J.K. Tuwei, president of Athletics Kenya, says in the report. “But it is what comes after that, if we do not act with sufficient urgency in addressing climate change, which worries me most. Incidences like athletes collapsing during or after finishing competitions, remind us of this threat and the impact of climate change on sports.” 

The report was published today by the British Association for Sustainable Sport (BASIS), a nonprofit trade organization whose members include major sports clubs and venues. University of Portsmouth physiologists Mike Tipton and Jo Corbett also contributed to the report, as did nonprofit research organization Climate Central. Nearly two dozen elite athletes — ranging from track & field stars to rowers, footballers, marathon swimmers, and more — added their testimonies about how brutally hot temperatures have affected them.

Tennis player Marcus Daniell, who, at the 2020 Tokyo Olympics, won a Bronze medal for New Zealand in the men’s doubles, wrote about how difficult it was to stay hydrated in the heat and humidity that year. That made headaches and lethargy “normal” during the Games, he says in the report.

For me it’s like you are in the build-up to the worst part of a bad flu – shivery and weird and hot and cold. Your mind can’t focus and your mouth is disgustingly dry. And the dangerous thing is that athletes often don’t know when to stop, because we’re conditioned to push ourselves beyond limits as a rule.” 

... “I am worried. I have been at tournaments where there have been double digit heatstroke withdrawals in a day. This is not how sport should be played.” 

The dangers are also there for swimmers diving into warming waters, British marathon swimmer Amber Keegan says in the report. World Aquatics (formerly FINA) set an upper limit for water temperature of 31 degrees Celsius (87.8 degrees Fahrenheit) for open water swimming after American athlete Fran Crippen died during a dangerously hot open water race in the UAE in 2010.

Physically, there are many impacts of extreme heat – cramp, fatigue (much more so than normal), and vomiting (which is especially bad as you’re losing the nutrition you’ve been consuming during the race). You don’t want to be using energy for cooling yourself down when you could be using it to swim faster.

That’s just the performance side, but from a safety side, if you’re struggling to think clearly, you’re not going to make a sensible decision about whether you’re overheating so much that you should be getting out. Of course, there is safety support, but at the end of the day it’s you that has to put your hand up and say “get me out.” 

Paralympic athletes also face risks when they compete in the Paris Games in August and September. Some competitors may have conditions that affect the body’s ability to thermoregulate. One survey of more than 100 athletes at the 2020 Tokyo Paralympics found that 21 percent of them reported experiencing at least one “heat stress-related symptom.”

The report lays out a set of recommendations to make sure that athletes can be at their best and that the audience gets a good show. That includes more structured guidelines for when to postpone or cancel an event because of the heat and proactively scheduling events for cooler times of the day or at cooler locations. Built-in water and cooling breaks can also be beneficial for competitors, support staff, and fans, the report says. It even calls on sports organizations to reassess their relationships with fossil fuel companies whose greenhouse gas emissions are causing climate change. “Sponsorship may bring in much-needed finance, but the long-term cost of such partnerships must be reassessed,” the report says.

In an email to The Verge, the International Olympic Committee (IOC) said it addressed many of the issues outlined in the new report in its “consensus statement on recommendations and regulations for sport events in the heat” published in 2022. That paper encourages greater collaboration among local, national, and international sports organizations. It also says athletes should “specifically prepare for the expected environmental conditions” at an event.

Local event organizers need to be transparent about environmental risks before and during the event and provide preventative measures and medical care for heat-related illness, the paper says. The IOC also said that the local organizing committee in Paris has worked with medical experts to keep athletes safe and healthy during this year’s games, which start in late July.