At the Tokyo Olympics in 2021, when temperatures reached possibly the hottest of any Games’ to date, athletes roasted. An archer fainted, and a table-tennis athlete reported “light heatstroke.” Organizers had already decided to move the marathon to Sapporo, on Japan’s northernmost island, but as the event approached, a heat wave wiped out any relief that latitude might have held. They nudged the race’s start time an hour earlier to avoid the day’s highest temperatures. Still, athletes were finishing in nearly 86-degree heat. Fifteen withdrew mid-race, and the winning time for the women’s race was a full 10 minutes slower than the winner’s personal best.
This Saturday and Sunday in Paris, the Olympic athletes in the men’s and women’s marathons might roast again. Milder temperatures at their morning start time might help, but they will be running in a heat wave. The 2028 Summer Olympics in Los Angeles could be even hotter. The world is getting warmer: Tokyo, for instance, has warmed more than 5 degrees Fahrenheit since 1900. Since Paris last hosted the Games in 1924, annual temperatures in the city have increased by 3.2 degrees. Heat, even for the best-trained body, is like a weight pressing down; so as long as the Summer Olympics remain in the summer, the fastest Olympic marathon times could be well behind us.
Muscles produce heat when they’re exercised; when the outdoor temperature and humidity are high enough to prevent that heat from dissipating, the body must slow. The cardiovascular system, the engine of any athlete, works overtime trying to pump blood toward the skin to cool the body, sapping energy from other parts of the athlete’s system. And in elite speed sports, every iota of energy counts.
Heat affects performance the most in distance races in cycling and running. “Sports that take longer than a minute and a half, two minutes to perform—high temperature can start to limit those for sure,” Brad Wilkins, a physiology professor at the University of Oregon who studies human performance, told me. In track and field, that means anything longer than the 800-meter race.
The longer a person must run, the greater toll the heat takes. So marathon times are most vulnerable to slipping. Relatively slow marathons are par for the course at the Summer Olympics, which tend to be held at the hottest time of year in their given city. Records are rarely broken in endurance events in the Summer Olympics—with the exception of swimming, for which the pool temperature is regulated, Wilkins said. One reason is that the gold medal is more important than the record; athletes are not trying to reach new heights of human achievement so much as they are trying to simply win. “But the second one is: It’s always hot.”
Already, the International Olympic Committee delayed announcing the location for the 2030 Winter Olympics while it met to decide how to account for the impact of climate change on future host cities. Warming winter temperatures are severely narrowing the roster of eligible hosts. The IOC announced last month that France will host the 2030 Winter Games in the French Alps, and Utah will host them in 2034. But the IOC president has remarked that due to climate change, by 2040, as few as 10 countries will have the appropriate climate for the Winter Games. After visiting Salt Lake City in April, a member of an IOC delegation said that the organization was “quite sure we could do it here until 2050, with all the climate reports we read,” but that 2060 and beyond poses a challenge even for the famous ski city. Maintaining cold-enough temperatures for winter sports may require moving the Winter Games farther north. And hypothetically speaking, the Summer Olympics might make more sense as a spring or fall event, although moving them to the Southern Hemisphere works just as well: The 2032 Summer Olympics, planned for Brisbane, Australia, will likely run in comfortable temperatures. It will, of course, be winter down under.
Outside of the Olympics, records are likely to keep getting broken until the true human limit is discovered, according to Michael Joyner, a physician at the Mayo Clinic and an expert in exercise physiology. He isn’t that worried about rising temperatures: People will find a way to work around heat, he told me. Races will move to colder months, and competitions may move northward. More events will be held indoors. And heat training—in which athletes train in hot conditions to improve their capacity to withstand them—will become a bigger part of athletes’ lives. “Heat training is the new altitude training,” he said. Chris Minson, a physiologist at the University of Oregon, found that training to withstand heat benefits athletes even in cool-weather races. He saw that if cyclists trained in 104-degree heat for 10 days, their VO2 max—the maximum amount of oxygen one’s body can take in and use while exercising—got a 5 percent boost. Their one-hour time trial got 6 percent faster, even in temperate conditions. Olympians in Paris have reported spending time in saunas and training in extra layers of clothing to prepare. “I guarantee everybody in Paris who’s doing anything in the track-and-field events that are longer than the 400 meter probably have gone through some sort of heat-acclimation protocol,” Wilkins told me.
Wilkins was part of a team sponsored by Nike that in 2016 attempted to create the perfect conditions in which to run the world’s fastest marathon. Engineers and physiologists designed every element of the event; the Kenyan marathoner Eliud Kipchoge ran a private race at an ideal temperature in advanced clothing and with other runners in front of him to cut wind resistance. He ran it in two hours and 25 seconds. High-tech shoes made the biggest difference, reducing his energy costs by 4 percent. In a similar experiment a few years later, Kipchoge broke the two-hour barrier, but the entire enterprise was so heavily engineered that it didn’t count as a true “marathon” for world-record-setting purposes.
The lesson? Advances in technology—training routines, nutrition, clothing, and more—are what support incredibly talented athletes like Kipchoge in reaching new heights of human performance.
Today’s elite runners and cyclists are no different from the ones who competed in the 1950s and ’60s: Humans have certainly not evolved into a faster species in that time. The men winning the Tour de France today, Joyner said, “are probably not any physiologically better than the great Eddy Merckx,” who won the event five times in the ’60s and ’70s. But most other elements of elite sport have changed. Bikes now allow riders to go faster with less energy input. The tracks that runners use have improved, reducing energy waste. Shoe technology has advanced dramatically. “I don’t see any slowing of world records, as long as the technology continues to be good and as long as people continue to focus on really setting up these races to get optimal performances,” he said.
In a 1991 paper, Joyner calculated the likely best possible VO2 max, lactate threshold, and running economy a person can achieve. If a runner could achieve all three at the same time, he wrote in the paper, the fastest possible marathon in natural conditions would be run in one hour, 57 minutes, and 58 seconds. That record has still not been achieved, but he imagines it will be, regardless of the march of climate change.
Wilkins is slightly less optimistic. “I grew up in the West. So I’ve watched fire seasons and how long they’ve gotten since I was a kid,” he said. He has a visceral sense of how climate change might be progressing faster than many people understand. So he can imagine that, 20 years from now, the fastest marathon time might slip back to 2 hours 10 minutes—that, especially for long-duration events that are impractical to hold indoors, times may begin to slow as temperatures keep rising. That might discourage more people from entering the sport, which would have a ripple effect of degrading the quality of competitions overall. “The less people you have in any sport, the lower the probability you have of finding the right factors of physiology and psychology in a human being that can actually perform these amazing feats,” he said.
Still, each time our conversation turned to the possibility that human potential in sport might truly be limited by the warming of the planet, Wilkins would pause and backtrack.
"Whenever I start to put hard limits on humans, I also start to hesitate,” he said. Limits on humans in sports have never proved true in the past. And technology we can’t imagine today may emerge to eschew the problem heat poses. “We are a creative species,” he said. Our bodies might not be able to adapt so quickly to the heat, but our behavior, and the ways we decide to handle this challenge, certainly could.
