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Mountaineers Reinhold Messner and Peter Habeler first proved that humans could climb to��the top of Mount Everest without using supplemental oxygen in 1978. But as of 2019, only 208 individuals��have ever achieved this feat—2.1 percent of the more than 10,000 people��to reach earth’s tallest��peak. Only one,��, a Nepali��climber known as the Snow Leopard, has pulled it off in winter.

But these exclusive clubs might soon have more��members, thanks to climate change.��

As the world becomes hotter, the air pressure around Mount Everest is increasing, according to a ��published in the journal iScience. As air molecules heat up, they gain more energy and move around faster, creating more pressure and density and bringing the oxygen molecules closer together. Meaning:��the higher the��air pressure, the more oxygen there is to breathe there,��even at Everest’s 29,029-foot summit.��The findings are part of a 2019��National Geographic expedition that studied��climate impacts on the Himalayas.

With an average global temperature��two��degrees Celsius (or 3.6��degrees Fahrenheit) warmer than that of��preindustrial times—the marker��when many climate scientists project we’ll see more dangerous climate-change impacts—air pressure is expected to increase a person’s maximum oxygen uptake by up to 4.9 percent at the top of Everest, according to the study. “It’s��like being lower in the atmosphere,” says��the study’s lead author, Tom Matthews, a climate scientist at Loughborough University in the United Kingdom.

Summiting Everest without supplemental oxygen is incredibly risky. “We always like to joke that you’re taking ten��steps per breath when you’re using oxygen,” says��Peter Athans, a world-renowned high-altitude climber who was involved in the National Geographic expedition. “When you’re not using oxygen, it’s more like ten��breaths per step.”

Even the simplest tasks can be exhausting at that elevation, says Sandra Elvin, who coordinated the 2019 trip.��Climbers become hypersensitive to headaches, are more susceptible to frostbite and hypothermia, and have greater difficulty making decisions.��

All of these risks are only amplified during the winter. Not only is the air pressure lower (on average it’s 5 percent lower at the summit during the��winter compared to its��highest point during summer monsoon season), but freezing temperatures and high winds from the jet stream that��engulf��the mountain can make the climb nearly impossible.��

That’s why most people who reach the summit without supplemental oxygen��(nearly 82 percent, according to the study) do so in the pre-monsoon month of May, the most popular time of year on Everest, a result of��the higher air pressure and��warmer, less windy conditions. October, after the summer rains subside, has historically been the next most successful time to make such an attempt. Soon, however, climbers may be able to tackle this challenge in the wintertime as well.��

As the study found, some of the most dramatic increases in air pressure are expected during this harsh season. If temperatures rise to the 3.6 degrees Fahrenheit mark, breathing in��this extra oxygen during the winter could feel equivalent to shaving off nearly 118 meters—387 feet—from your climb.��“You can pick a day that makes it feel like you’re climbing in spring,” Matthews says. “It doesn’t have to be a difficult winter ascent in terms of oxygen availability.”

New climbers forgoing extra oxygen—both in the winter and the spring—would be joining a subset of climbers who each have their own philosophy on oxygen-less climbs. “You need motivation, you need something special, you need to do it for yourself,” says��Spanish alpinist��Alex Txikon, who last year attempted to summit Everest during the winter without supplemental oxygen before being beaten back by bad storms. But, he admonishes, climbers shouldn’t try to break records for the sake of it. “It’s not something you do to become famous,” he says. “The first rule is not to destroy your career, your life, just because of the ego.”

In addition to increased oxygen, the shifting seasons in a warmer world are further opening up opportunities to summit��Everest. When Athans first started climbing in the early 1980s, the winter season began in October. These days, he says, the monsoon season is extending and the traditional fall season is now starting later. “We’ve frequently seen in recent years that��late November and December can be excellent times to climb,” he says. During the��two-month-long National Geographic��expedition, Matthews��helped install the ��on Mount Everest;��sitting at 27,650 feet, it��will��provide��precise��forecasts that can be of help to those planing an��ascent.��

There is the chance��that better forecasts and seemingly more favorable conditions could spur riskier��behavior on the mountain, according to Matthews. Having more specific weather information from the station high on��Everest��could create a sense of safety that might cause��climbers to miscalculate other critical details, like the amount of time the ascent��might take or how much bad weather��they can��endure. Still, Matthews says,��“It’s��the world’s best climbers that are at the absolute forefront of their profession, that are trying to do this in the first place, and I think really what this does is it helps fine-tune those preparations.”��

Panuru Sherpa, cofounder and executive director of Xtreme Climbers Treks and Expeditions, says��he has noticed a change in Everest’s air pressure and oxygen content in his 30 years of climbing (and ). But according to him, these factors��alone aren’t��enough to make the mountain easier to overcome; climate change is also bringing with it new difficulties:��Glaciers are shifting and shrinking.��More crevasses are appearing higher up the mountain. The notorious Khumbu Icefall could become more treacherous to pass. And , making it harder to scramble up as snowpack dwindles. Climate change, says Panuru, has definitely made it “more challenging and more dangerous to climb Everest.”

Most experts agree. The final stretch to the summit might be a bit easier these days, says��Athans, while the bottom half of the mountain could become trickier to navigate. But��he says��that’s just “the challenge of mountaineering—being able to adapt to your environment, to be able to deal with whatever it throws at you.”