Roof of the World

Want to climb Everest? New study identifies factors that influence success

"It is no longer a few people alone on the mountain."

Born from the collision of the Indian and Eurasian tectonic plates, the highest point on Earth is catnip for adventurers. Mountaineers have attempted the summit of Mount Everest for almost a century. But, the first successful ascent wasn’t made until 1953. As of spring 2019, 4,346 brave souls have reached the summit, having battled immense physical and psychological challenges.

And despite a deadly 2019 Everest climbing season, the success rate of summiting the mountain has actually doubled in the last three decades, according to new research. The death rate, meanwhile, has been constant since 1990; hovering at around 1 percent.

The study teases out why more people are succeeding, and, in turn, provides critical insight for climbers who dream of making their own attempt. It is the most comprehensive examination of Everest success and death rates to date.

Raymond Huey is professor emeritus of the University of Washington and the study’s lead author. He tells Inverse that he became interested in the ascent of Everest in 1995, when he attended a lecture by Reinhold Messner, whom Huey describes as “the greatest Himalayan mountaineer ever.”

Messner argued against using supplemental oxygen during the summit, and Huey, as a physiologist, immediately thought climbing Himalayan peaks without supplemental oxygen would be very dangerous. Huey wondered if there were data to test Messner’s ideas. Soon he realized he would need to compile it himself.

He collaborated with Elizabeth Hawley, the late Reuters correspondent based in Kathmandu, Nepal, who followed mountaineers attempting peaks in the country, and Richard Salisbury, a climber and computer analyst.

Salisbury built The Himalayan Database from Hawley’s records, and the new study uses it alongside information collected by German journalist Billi Bierling, the designated successor of Hawley, since 2016. The data include details on each individual climber’s age, sex, host country, prior experience, as well as the factors that likely contributed to their success — or caused their death.

The findings were published Wednesday in the journal PLOS ONE.

A view of a Everest Base Camp in May 2020.Getty Images

Huey approached the data like an evolutionary biologist would approach most subjects, he tells Inverse.

“The kinds of questions we’re asking — whether success and death are rated to age or sex — are the kinds of questions, and the same kinds of analytical techniques, that evolutionary biologists ask about sprint speed or bill length in Galapagos finches," he says.

Huey and his colleagues analyzed and compared the success and death rates of first-time climbers who attempted to summit Everest either between 1990 to 2005, or 2006 to 2019. In the first period, there were 2,200 climbers; in the second, there were 3,600. Success was defined as reaching the summit and surviving.

Certain patterns emerged, including the findings that:

  • Summit success rates doubled between the two periods, changing from one-third of climbers successfully reaching the summit to two-thirds.
  • More women have attempted to summit in recent years — specifically, 9.1 percent of climbers were female in the first period as opposed to 14.6 percent of climbers in the second.
  • Women and men have similar odds for both success or death.
  • A 60-year-old climber from the second period had the same success rate as a 40-year-old climber in the first; about a 40 percent chance.

What makes for a successful Everest climber — Generally, the odds of success are improved by youth and prior experience with high elevations, Huey says.

But the definition of an “ideal climber” changes with the climber’s goal, Huey notes. In the early days, the goal was to get at least one member of an expedition to the summit, he says. At that time, “team players” were key.

Next, came “an era when climbers tried many bold and daring routes,” Huey says. The goal was not just to summit, but to try something new.

“That called for stamina, boldness; experience,” he explains.

“Sadly, many died.”

In recent years, the goal is to simply get to the summit – but this has also meant climbing on packed trails. The fact that Mount Everest is now a crowded destination teeming with inexperienced climbers is thought to be a driver of recent deaths.

“It is no longer a few people alone on the mountain,” Huey says. “Now, I think the key traits are being relatively young, say 25 to early 40s, having prior high elevation experience, and having the patience to climb in a line with many others.”

Better weather forecasting, fixed lines on popular routes, increased experience of expedition leaders and high-altitude porters, and more climbers using supplemental oxygen are also all drivers for the increase in success rates, the study suggests. Completing the summit without this help requires incredibly intense training.

A more accurate look at Everest — Huey explains that, prior to the Himalayan Database, people only knew how many people summited or how many people died. They didn’t know how people were at risk — those who go beyond the Base Camp, with the intent to summit. Many of the other data about Everest in the public sphere were wrong, he adds.

“To calculate a success rate, you need the number of people who summited divided by the number attempting,” Huey says. “To calculate the death rate, you need the number who died divided by the number attempting the peak. So people had only the numerators, not the denominator.”

People would calculate the death rate by dividing the number of people who died by the number who summited — the wrong denominator. This led to inaccurate ideas about how many people who climb Mount Everest die in their attempt.

The main factor that could topple the climbing success rate of Everest climbers is overcrowding. Each spring, more than 500 climbers attempt the summit during a small window of favorable conditions. Huey wants to perform a more in-depth analysis of the effects of crowding but, with permits on pause because of Covid-19, he’ll have to wait for the pandemic to pass to collect the critical data.

Abstract: Mount Everest is an extreme environment for humans. Nevertheless, hundreds of mountaineers attempt to summit Everest each year. In a previous study we analyzed interview data for all climbers (2,211) making their first attempt on Everest during 1990–2005. Probabilities of summiting were similar for men and women, declined progressively for climbers about 40 and older, but were elevated for climbers with experience climbing in Nepal. Probabilities of dying were also similar for men and women, increased for climbers about 60 and older (especially for the few that had summited), and were independent of experience. Since 2005, many more climbers (3,620) have attempted Everest. Here our primary goal is to quantify recent patterns of success and death and to evaluate changes over time. Also, we investigate whether patterns relate to key socio-demographic covariates (age, sex, host country, prior experience). Recent climbers were more diverse both in gender (women = 14.6% vs. 9.1% for 1990–2005) and in age (climbers > 40 = 54.1% vs. 38.7%). Strikingly, recent climbers of both sexes were almost twice as likely to summit–and slightly less likely to die–than were comparable climbers in the previous survey. Temporal shifts may reflect improved weather forecasting, installation of fixed ropes on much of the route, and accumulative logistic equipment and experience. We add two new analyses. The probability of dying from illness or non-traumas (e.g., high-altitude illness, hypothermia), relative to dying from falling or from ‘objective hazards’ (avalanche, rock or ice fall), increased marginally with age. Recent crowding during summit bids was four-fold greater than in the prior sample, but surprisingly crowding has no evident effect on success or death during summit bids. Our results inform prospective climbers as to their current odds of success and of death, as well as inform governments of Nepal and China of the safety consequences and economic impacts of periodically debated restrictions based on climber age and experience.
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