LOVELL CANYON, Nev. — It was 73 degrees and the early-morning sun was still rising over the Mojave Desert as nearly six dozen long-distance runners gathered at the start line and anxiously watched numbers tick down on the digital clock overhead.

“Make sure that you’re staying on top of your internal hydration and your external cooling,” the race organizer said into a microphone.

Game Changer This series will examine the impact climate change is having on the world of sports, from elite competitors to recreational athletes.

The runners shook their limbs loose and bobbed in place, eager for the start. The annual race is called Running with the Devil, and it takes place less than 30 miles from the glitzy air-conditioned casinos on the Strip in Las Vegas. The forecast called for an unseasonably cool day in the desert, but the racers — running a marathon, 50 kilometers, 50 miles or 100 kilometers — had assembled specifically for a physiological test in the heat.

The people from this area are plenty acquainted with hot summer days. Climatologists say many of the Earth’s hottest places are only getting hotter. There was a report this year that found Las Vegas is the fastest-warming city in the country, due in part to urban heat island effect, and has seen an average temperature increase of nearly 6 degrees Fahrenheit since 1970.

The whole planet is getting warmer, in fact. Across the globe, the past four years are the warmest on record. Last year the average temperature across Earth’s land and ocean surfaces was 1.42 degrees Fahrenheit above the 20th-century average, according to the National Oceanic and Atmospheric Administration, and climate watchers say it’s trending in one direction. Climate projections suggest the planet could warm by 3 or 4 degrees Celsius by the end of this century, which would have major ramifications for outdoor sports everywhere, from recreational weekend joggers to elite athletes competing on the biggest stages.

Ryan Moshinsky, a 50-mile runner, douses his head with water after finishing the race. At 21, he was the youngest ultra runner in the field. (Jonathan Newton/The Washington Post)

“When you talk about climate change and you tell someone it’s a degree hotter — Pfft! — that doesn’t seem like very much,” explained Andrew Grundstein, a climatologist at the University of Georgia. “When I talk to my students about the difference in a couple degrees, I tell them, ‘Remember, when it was 4 degrees [Celsius] cooler, we were in an ice age.’ ”

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From community races to the Olympics to the World Cup, event organizers are already having to make adjustments to competition schedules and start times. And athletes around the world are having to take more precautions as science and technology evolve to help them cope with the heat — or, in some cases, gain a competitive advantage.

Events such as tennis’s Australian Open have instituted safety measures to account for extreme heat. The International Olympic Committee and FIFA have formed committees to study heat-related issues at major events. Next summer’s Olympics in humid Tokyo will feature a marathon that starts at 6 a.m.

This year’s track and field world championships are in scorching-hot Qatar, where organizers will start the marathon at midnight. The World Cup men’s soccer tournament, which usually takes place in June every four years, has been pushed back to November and December when Qatar hosts in 2022 in hopes of cooler weather.

Florian Henig, a 100-kilometer runner, leaps over a creek to keep his feet dry at Lovell Canyon. Running with the Devil race participants are shown at the start/finish line in Lovell Canyon. Suzy and Nichole Hanson cheer on the long-distance finishers as they prepare to run the nighttime 5K. (Jonathan Newton/The Washington Post)

TOP: Florian Henig, a 100-kilometer runner, leaps over a creek to keep his feet dry at Lovell Canyon. BOTTOM LEFT: Running with the Devil race participants are shown at the start/finish line in Lovell Canyon. BOTTOM RIGHT: Suzy and Nichole Hanson cheer on the long-distance finishers as they prepare to run the nighttime 5K. (Jonathan Newton/The Washington Post)

The Running with the Devil race, intentionally scheduled for extreme conditions, might not be an exact peek into the future, but it does highlight many of the challenges already confronting much of the sports world. How does heat affect performance? What dangers lurk on the outdoor courses and fields exposed to the summer sun? How does one stage a safe event in extreme conditions?

The racers had various strategies, and at the start line, they wore long sleeves or no sleeves or no shirts, some armed with backpacks, running belts and water bottles. They stared ahead at a desolate one-lane road with regular mile-markers and irregular roadkill. The landscape was a blend of browns and greens with Joshua trees, rabbitbrush and Ponderosa pines lining the route, chipmunks, lizards and rabbits providing the only company.

Finally, at 7 a.m.: “Going off in 5, 4, 3, 2, 1 — Go!” the race director said to the sound of claps and cowbells that rang out in an otherwise quiet, empty, warming desert.

‘It’s pretty extreme’

It was 95 degrees and sticky in Orlando but 30 degrees cooler inside air-conditioned Orange County Convention Center. A crowd of more than 6,000 gathered in late spring for the annual meeting of the American College of Sports Medicine, the largest such gathering in the world.

Heat-related topics have become a staple of these meetings, and about 200 people — athletic trainers, doctors, researchers, physiologists and performance coaches among them — gathered in Room 303 for a presentation focused on next summer’s Olympics. Doug Casa, head of the Korey Stringer Institute who serves on a commission dedicated to heat-related issues for the Tokyo Games, offered the crowd a brief history lesson.

“The 1964 Tokyo Olympics, they moved to October because of the brutal heat in Tokyo,” he said. “Well, it’s hotter in Tokyo now than it was back in 1964. . . . There’s no movement this year. It’s happening at the end of July and August in the most brutal conditions that you can imagine.”

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With an anticipated average temperature of nearly 90 degrees and humidity topping 55 percent, the Olympics will be on par with some of the hottest athletic events ever staged.

“It’ll be the hottest Summer Olympics in history,” Casa said. “It’s pretty extreme.”

The professionals in the large conference room assembled to discuss ways to keep the world’s best athletes safe and somehow maximize performance in such difficult conditions. Endurance athletes with prolonged exposure are more susceptible to the dangers posed by heat, while some athletes — sprinters, for example — might actually perform better. But almost any athlete competing outdoors will face risks.

One key to competing in heat is for athletes to acclimatize — to arrive at the destination early and exercise for at least seven to 10 days in the hot conditions. The prolonged exposure allows the athlete’s body to adjust: Plasma volume increases, heart rate decreases, sweat rate increases, and skin and core temperatures stabilize.

Athletes run a marathon, 50 kilometers, 50 miles or 100 kilometers — assembled specifically for a physiological test in the heat. (Jonathan Newton/The Washington Post)

Among those in the Orlando crowd was Randy Wilber, the chief physiologist for the U.S. Olympic & Paralympic Committee who has worked with Team USA athletes since 1993. He has been considering all of these factors since Tokyo was awarded hosting rights in 2013.

“The bottom line is it’s going to be very hot, very humid. That’s not any surprise,” he said. “It’s how you react to it that matters.”

Wilber has already devised heat plans with his U.S. colleagues. The Tokyo conditions might not lend themselves to world records in many events, but coaches, athletic trainers and physiologists can still help get the athletes onto the podium.

“If we do this right — if we prepare for the heat and humidity right — we could beat some people who would normally blow us up,” Wilber said. “So that’s a pillar of our strategy: If we can out-science our opponents, our chances of doing better are good because these are things that some people won’t pay as much attention to.”

To that end, the various U.S. teams have mostly sorted out travel plans so athletes will arrive well ahead of the Opening Ceremonies, as early as two weeks for some sports. Some will attend training camps in the region, and they’ll also utilize a U.S. training center in Tokyo.

Those who compete in some outdoor sports, such as the track and field athletes, will be sized for specially engineered ice vests. They’ll be encouraged to wear the vests on bus rides to the stadium, during their pre-competition warm-up, in the staging area and then again post-event to cool down.

“Our job is to make sure they’re prepared for any situation and their body is ready for the heat and humidity on competition day,” Wilber said.

Natalia Murua, a 50-mile runner, dunks her head with ice water at one of the aid stations on the course. (Jonathan Newton/The Washington Post)

Oppressive heat

It was 82 degrees under the cloudless sky as the runners on the desert course began to feel the midday heat. Virtually any training run in Nevada can be dangerous, especially for those who aren’t acclimatized and if conditions and hydration levels aren’t closely monitored.

Runners have had to be airlifted off the Running with the Devil course before, and the 2013 race was canceled altogether when the forecast called for 117-degree heat. Organizers know they have to take precautions, and water jugs and aid stations are located about every three miles, with more than 3,000 pounds of ice available along the course.

At one station, about halfway through his 100-kilometer race, Martin Gruebele, 55, asked for another scoop of ice for his hat as he prepared for a steep incline. “When that baby runs out, I am walking,” he said, setting the hat atop his head.

As the temperature climbed, race volunteers kept a closer eye on the runners. The ACSM recommends halting any training and practice activities at 90 degrees. That’s a familiar temperature in the Mojave Desert, but Grundstein, the Georgia climatologist, led a 2013 study that suggests the entire country will be experiencing more dangerously hot days in the future and the sports world needs to ready itself.

“Expected climate change will lead to a considerable increase in the frequency of days with conditions deemed unsuitable for sports activity across much of the U.S.,” the study found.

The Southeast, the Gulf Coast and Arizona could average 30 to 50 days of oppressive heat in some areas — and as many as 85 such days in some spots. Other areas, such as New England, the Pacific Northwest or the upper Midwest, which presently have fewer than five oppressive days annually, could see 15 to 30 per year. Just last week, the temperature in Alaska hit 90 degrees for the first time in recorded history.

In the desert, only the ultramarathoners were left by late afternoon as temperatures started peaking. Many of the runners who registered were curious to learn how their bodies respond to the heat. Gruebele is a renowned biophysicist who studies animal motion. “Might as well do some experiments on yourself,” he said.

In last year’s race, he had struggled in the heat, losing eight pounds. He dropped down in distance from 100 miles to 50 and found himself crawling across the finish line.

He was armed with a new prerace strategy — Gruebele did sauna training to increase his heat tolerance — and was determined to conquer the elements. He felt he was finally appreciating the complicated, substantial impact heat has on an athlete’s body.

Athlete vs. body

It was 59 degrees outside on a May afternoon in Storrs, Conn., but behind a giant door that looks better-suited for a bank vault, the temperature was cranked way up.

Julie Dunkle, 52, had traveled across the country because she wasn’t happy with how her body had been responding to heat. Dunkle is a triathlete who builds her year around the Ironman World Championship in Kailua-Kona, Hawaii. It’s one of the most demanding sporting events on the planet and takes place in some of the most unforgiving conditions. It starts with a 2.4-mile open water swim, followed by 112 miles on a bike and then capped with a 26.2-mile marathon run. It all unfolds in heat and humidity that wraps itself around competitors and squeezes until they can barely breathe.

Dunkle has competed in all types of conditions. But at the Ironman, her body fails her, her muscles seize, and her stomach turns into a blender. She sweats profusely and vomits a half-dozen times or more. She has lost as much as 11 pounds over the course of a race.

Her body is a puzzle Dunkle keeps trying to solve, so she came to the Korey Stringer Institute at the University of Connecticut for two days of heat testing. She was sealed into the climate chamber, where staffers were able to mimic the Ironman conditions: 91 degrees with 63 percent humidity.

“It feels just like Kona,” Dunkle thought when she stepped inside the small room 5,000 miles from Hawaii.

The chamber allows staff members to re-create environmental conditions from anywhere on the planet. The goal is to put athletes in those extreme conditions and monitor how their bodies respond.

“If your temperature is 102.5 instead of 104, you’re going to perform better. It’s that simple,” said Casa, head of the institute. “Because if your temperature is lower, you’re not sending much blood to the skin surface, and there’s more blood for your heart and your muscles.”

Dunkle was nearing the end of a two-hour bike ride, and her temperature kept inching upward and reached 102.6. She had lost about a half-gallon of fluids, much more than she could replace.

“How you feeling?” asked Robert Huggins, the lab’s president of research and athlete performance and safety.

“Not great,” she said. “I feel thirsty, but I can’t drink anymore.”

As her temperature rose, her power output fell, unable to maintain her target pace.

“Think of it like a car,” Huggins explained. “How fast can I make the engine go without making it overheat?”

As extreme heat becomes more prevalent and events are increasingly staged in oppressive conditions, athletes who struggle in heat can expect to see their performances affected and will need to take added precautions in training and during competition.

Heat stroke generally strikes when the body temperature reaches 104 degrees. When the body can no longer cool itself, blood stops reaching vital organs and the brain, heart, kidneys, lungs, liver and muscles can begin to malfunction. The symptoms can vary, but with the central nervous system compromised, athletes can experience dizziness, fatigue, headaches, seizures and nausea. They could pass out and lose consciousness altogether.

Unlike cars, humans don’t come equipped with a temperature gauge to know when they’re entering dangerous territory. Casa said there are two “holy grail” pieces of technology that could be on the market in the next couple of years: a wearable assessment that measures an athlete’s hydration status and another that offers real-time monitoring of core body temperature. Within the next few years, Casa said athletes will be able to swallow a capsule that can transmit data to a smartphone, watch or bracelet.

After a brief rest, Dunkle began running on a treadmill. Barely 40 minutes in, that familiar feeling bubbled in her stomach. Her heart rate reached 170 beats per minute. She saw black spots, and her head started pounding. Dunkle stepped off the treadmill and buried her face in a towel. She was done for the day.

“That sensation you felt, that’s your body telling you that you’re getting too hot,” Huggins told her.

Dunkle’s body temperature had reached 103.9 degrees and was still climbing, and she had lost 6.7 pounds — 4 percent of her body mass — in 2½ hours of exercise.

A month later, Dunkle and Huggins got on the phone to discuss the test results. He recommended she avoid hot races. If she insisted, he told her that she needed to slow down.

Dunkle was close to tears. “Why even try again?” she thought.

But she also knew she couldn’t just quit. She planned to arrive in Hawaii three weeks early for October’s Ironman, allowing her time to acclimatize, and then hope that on race day conditions are favorable and her body agreeable.

The way she sees it, it’s not just her trying to conquer an island; it’s an athlete battling her body.

Susan Moshinsky walks the final three miles to keep her son, 50-mile runner Ryan Moshinsky, motivated to finish. “I brought him into this world; I’m taking him to the finish line,” she said. (Jonathan Newton/The Washington Post)

‘More pain than I’ve ever been in’

It was 90 degrees in the late afternoon back in the desert. As the sun dipped lower, shadows began appearing along the course and runners were reduced to walking for long stretches.

Ryan Moshinsky took respite in a folding chair at one aid station, momentarily contemplating life and the decisions that had brought him here. The 21-year-old was the youngest ultra runner in the field. He had never even entered a marathon before, but Moshinsky had targeted Running with the Devil a year earlier, ambitiously registering for the 50-miler.

But running near his home in the Chicago suburbs is not quite like the desert, and the race was unfurling all of its weapons on the young runner. To avoid chafing, he chose to run shirtless, which left him directly exposed to the sun. After 23 miles, he threw up part of his sandwich and couldn’t stomach another bite. Around 26 miles, his legs began throbbing. Then around Mile 37, his chest and neck started aching, and Moshinsky thought he was finished.

“More pain than I’ve ever been in my life,” he said.

Moshinsky was nauseous and his gait was more of a stumble. He was alone in the desert for long stretches, but at the 44-mile mark, he was permitted a pacer, and a cousin walked with him for three miles before his mother took over for a final leg.

“I brought him into this world; I’m taking him to the finish line,” Susan Moshinsky announced.

The two walked side by side, with Susan telling jokes and stories to keep her son alert. Only a dozen racers remained on the course. Unlike last year, Gruebele cruised through 100 kilometers. He lost only one pound this time, though truth be told, he wished it had been hotter.

Heat affects competitors differently. Rising temperatures have forced athletes and event organizers to make major changes and, at times, lower expectations. Moshinsky had come too far to quit. He splashed water on his arms and shielded his head and shoulders from the sun with a towel. With a quarter-mile left, Moshinsky started running again, sensing the finish line was near.

More than 11 hours 12 minutes after he started, Moshinsky’s run in the sun was finally over. It was down to 80 degrees, but the dry desert air felt hotter. He had just enough strength left to briefly lift his arms in the air before collapsing into a chair.

“Sit down,” his mother implored. “I love you, but don’t do that again. You’ll give me a heart attack.”

Running with the Devil race participants pose for a group shot before their journeys. Athletes around the world are having to take more precautions to cope with the heat. (Jonathan Newton / The Washington Post)

Story by Rick Maese, photos by Jonathan Newton, design by Cece Pascual, photo editing by Thomas Simonetti.