The success rate of summiting Mount Everest, the world's tallest peak, has doubled in the last three decades, while the death rate for climbers has hovered unchanged at around 1 percent since 1990, according to a study.
Researchers at the University of Washington and the University of California, Davis, in the US also found that the number of climbers on Mount Everest has greatly increased, crowding the narrow route through the dangerous death zone near the summit.
The findings, published on Wednesday in the journal PLOS ONE, analyzed the success and death rates for all first-time climbers who had a permit to summit Everest during the period of 2006 to 2019. The study shows that the summit success rates from 1990 to 2019 have essentially doubled; two-thirds of climbers now reach the summit, verses one-third previously.
The researchers found that the overall death rate of around one percent hasn't changed. They also found that a contemporary 60-year-old climber has the same success rate of about 40 percent as a 40-year-old climber in the prior period, suggesting "60 is the new 40" when it comes to summiting the Everest.
A contemporary 60-year-old climber has the about the same death rate -- about 2 percent as a 48.5-year-old in the earlier period, according to the researchers. They also found that more women are attempting the climb in recent years (14.6 percent) versus the previous period (9.1 percent), with women and men having very similar odds of success or death in both periods.
The doubling of the summit success rate is likely due to a number of factors. Weather forecasting has dramatically improved since the "Into Thin Air" storm of 1996, giving climbers more information on the best window to push for the summit, according to the researchers.
Some climbers are using elevated flow rates of supplemental oxygen -- and doing so lower on the mountain, they said. The most popular routes have fixed lines, meaning climbers can clip into ropes tethered to the mountain for their ascent and descent, making it safer if they fall, the researchers noted.
Increased experience of expedition leaders and high-altitude porters may also have helped boost success rates, according to the researchers. Interestingly, while more climbers are making it to the top in recent years, today's climbers are actually less experienced in climbing tall peaks in Nepal than climbers who attempted Everest in the 1990s and early 2000s, they said.
Mount Everest draws over 500 climbers each spring to attempt the summit during a small window of favorable conditions on the rugged Himalayan mountain that tops out at just over 29,000 feet. The study identified patterns in the characteristics of mountaineers -- such as age, sex, and prior experience -- that might influence their likelihood of summiting or dying during the spring climbing season.
"Mount Everest is still a very dangerous mountain, and climbing it will never become a walk in the park because it's way above the limits of what most people can do," said study lead author Raymond Huey, a professor at the University of Washington. "Unfortunately, reported statistics of risk on Everest are often inaccurate," Huey said.
The researchers said they have provided accurate information on the chances of success and on the chances of dying, thereby helping climbers make an informed decision about whether to attempt this great peak. These patterns also can help Nepal and China in deciding whether to institute restrictions on climbers such as maximum age or experience level, Huey added.
Previously, the team applied the same statistical methods to climbers during the period of 1990 to 2005, and, as a result, they were able to compare success and death rates between the two periods. From 1990 to 2005, more than 2,200 first-time climbers attempted to summit Everest, according to the researchers.
From 2006 to 2019, that number increased to more than 3,600 climbers, they said. The researchers focused on climbers with paid permits, excluding climbers with additional tasks -- such as high-altitude porters, photographers and support staff -- along with those who attempted to the summit in other seasons, or who were attempting the summit for the second time or more.
They also excluded a handful of years from the analyses when extreme events such as icefall avalanches or earthquakes led to cancellations of the climbing season. The team also looked at the effects of crowding near the summit for the past two climbing seasons.
Detecting possible effects of crowding is difficult with available information, the researchers said, but their analysis didn't show any impacts of crowding on success or death rates. However, crowding must slow climbers, increasing their exposure in the death zone, they added.