About 250 climbers reached the summit of Mount Everest during a 48-hour period of good weather this weekend. Sandra Leduc of Ottawa reached the summit on Saturday and Canadian mountaineer John Stephen reached the summit on Friday.

During the previous weekend, May 18-20, which saw the first good break in the nasty weather this climbing season, hundreds of climbers were trying to reach the summit at once. Six of the climbers died,  four climbing from the south and two from the north, making it one of the deadliest 48 hours ever for Everest climbers.

Debate followed about whether the large number of climbers on Everest contributed to at least some of those deaths. But that is probably only part of the story, experienced climbers say.

The six who died had all successfully reached the top, Canadian Shriya Shah-Klorfine among them.

There are still unanswered questions about what happened in her case but reports are that she died about 50 metres below the summit, still in the so-called death zone where oxygen levels are low and the slopes are steep and icy. 

Like many climbers, Shah had arrived in the high-altitude region at the end of March. That gives the body time to acclimatize before attempting a push to the top.

In the spring, the weather window for a successful Everest climb runs from early May to early June. Until the weather breaks, the climbers bide their time at base camps. When the first good break came a week ago, an especially large number of climbers had been waiting and took off as soon as they could.

Climbers on the southern approach, which was pioneered by Edmund Hillary and Tenzing Norgay in 1953, ascend following a rope line that runs over almost 10 kilometres to the summit.

Running out of oxygen

Nick Heil, a climbing instructor and author of Dark Summit: The True Story of Everest's Most Controversial Season, writes, "On summit day, you race the clock, trying to get up and down before your oxygen runs out and your body gives in to the hypoxic environment," which can lead to pulmonary or cerebral edema.

This time it was a slow race, due to traffic jams enroute.  A guide with Shah's Utmost Adventure Trekking, Ganesh Thakuri, told CBC News, "We had to wait 2½ hours for the traffic to pass the route."

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Shriya Shah-Klorfine, of Toronto, waits at Everest's base camp on May 12. She died shortly after achieving her dream of scaling Mount Everest. (Canadian Press)

Thakuri claims he asked Shah, "to go back and try next year or some other year," adding: "But she didn't listen."

With the delays, Thakuri said that on her descent, Shah ran out of oxygen bottles and died.

That high up, it helps a climber to have oxygen bottles but they are not essential. As of 2006, 144 successful summits of Everest had been made without supplementary oxygen, according to AdventureStats.com.

Still, the fatality rate is about twice as high for those attempting to reach the summit without supplementary oxygen compared to climbers using it, according to the website.

In an interview with CBC News, veteran mountaineer Alan Arnette noted that, "the best expeditions, like Peak Freaks or IMG [International Mountain Guides] or Alpine Ascents, they will actually send up extra Sherpas carrying extra oxygen for their team in case there's a malfunction, or in case there's an emergency."

Weather a determining factor

As far as the Shah climb went, the delays may not have been fatal had the weather not taken a sudden turn for the worse. Adding to the inhuman cold, a windstorm swept into the area, trapping climbers who were ascending and descending.

Eric Simonson, one of the world's top mountaineering expedition leaders and the author of two books about climbing Mount Everest, understands the dilemma Shah faced when she had to decide whether to continue or go back.

He successfully climbed Everest in 1991. But he also told CBC News that in other years he "turned back three times, because it wasn't right."

"It's hard to turn around and go down and not make it when you've invested so much into it," Simonson allowed.

Simonson also directs IMG's Himalayan programs and has 10 expeditions under his belt, including two this month. IMG's first team had 11 climbers and 11 Sherpas on the summit on May 19, with the second team of 12 climbers and 14 Sherpas reaching the peak early on May 26.

Climbing Everest from the north vs. the south

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Sam Wyatt of Vancouver reached Mt. Everest's summit from the north the same day there was a traffic jam climbing from the south. Wyatt said there were no bottlenecks on the northern route. (Courtesy Sam Wyatt)

While climbers on the south slopes faced traffic jams last weekend it was another story for mountaineers approaching from the north. That's the route that Sam Wyatt and Steve Curtis were on. Wyatt spoke to CBC News from his hotel in Kathmandu, Nepal's capital. 

Along with Wyatt and Curtis, there were about 75 people trying to climb Everest from the north but there were no bottlenecks, Wyatt said.

While the climbers on the south have a higher success rate, they follow the same rope and "so it's very easy for people to get bunched up and trapped behind each other." On the north, "the climbing's much more technical, so as a result, the field of climbers gets spread out more."

Wyatt said that when they reached the summit they were able to see a line of people approaching from the other direction, and that the number of people on that line was getting larger.

Wyatt said the lineups occur, "not because the mountain's not big enough to accommodate everybody, it boils down to the weather windows."

With almost all the climbers using weather forecasts and getting similar weather advice, "everybody winds up going up on the same day because those are the best weather days." So when there are more good weather days, the lineups are shorter, and vice versa.

Wyatt explained that on the north side this was actually a very light year. He estimates that in total there were about 200 climbers, half of them Sherpas.

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Two Guinness World Records holders, Tamae Watanabe of Japan, at 73, the world's oldest woman to climb Mount Everest, and Apa Sherpa, who has summited Everest a record 21 times, attend a press conference in Kathmandu, Nepal on May 25. (Navesh Chitrakar/Reuters)

By contrast, there were about twice that number in 2009 when Wyatt attempted and failed to reach the summit, due to weather conditions.

This year, 73-year-old Tamae Watanabe of Japan reached the summit from the north side, becoming the oldest woman to climb Everest and breaking the previous record, which she had set in 2002.

Government issues expedition permits

Permits to climb from the south are issued by the government of Nepal, and cost about $10,000 per expedition. Simonson explained that sometimes smaller outfitters band together and climb under the same permit. This year, permits for about 32 expeditions have been issued.

Rita Limbu of Gorkha FM Radio in Kathmandu told CBC News that although Everest expeditions are an important source of income for Nepal's government, the safety situation is not a big issue right now because of the focus on the political situation in the country. (Nepal is trying to draft a new constitution after years of civil war.)

Everest ascents by the numbers

  • During summit bids on Mount Everest from 1950-2009, 44 per cent of the deaths of expedition members, excluding Sherpas and other hired help, were a result of falls.
  • About 80 per cent of members' deaths during summit bids, 1950-2009, happened on the descent and just 20 per cent on the ascent.

Source: Richard Salisbury and Elizabeth Hawley, The Himalaya by the Numbers 

Some people have called on the government to limit the number of permits it issues, an idea that Wyatt, for one, rejects. "It's mountaineering, what's government got to do with it? Some bureaucrat's going to really know who's going to be able to go and who shouldn't?"

Wyatt argues that "people need to understand that they're climbing the highest mountain on the planet, that there's a genuine risk of dying and they should plan accordingly."

In recent years, slightly less than one of every hundred climbers who tried to climb Everest died in the attempt, according to Adventure Stats.

According to Arnette, the government does not regulate the guide services, so he stresses the importance of going with a good one. "Anybody can put up a website, put up content and claim they're a guide and offer a low price," he said.

Simonson, from the highly-regarded IMG, said his company first reviews the resumés of would-be climbers. "We won't take someone who we don't think can make it."

Climate change increases Everest risks

Another well-known company, Himalayan Expeditions, pulled out in early May because they felt the conditions on the ground were unsafe.

Long-term, these conditions may only worsen as some experts feel that climate change is altering the all-important weather window and the geography.

Writing in the New York Times a few days before last week's deaths, guide and author Freddie Wilkinson argued that global warming "is slowly yet steadily drying out the Himalayas, resulting in rockfalls, avalanches and sérac collapses."

Wilkinson added that "this season, hampered by dry conditions, the mountain has been dangerously alive. Last week, rock fall on the Lhotse Face resulted in a half-dozen serious injuries, and one very near miss was reported when a titanic avalanche ripped between camps 1 and 2, thundering completely across the valley and obliterating the trail."

Apa Sherpa, the Nepali mountaineer who holds the world record for the most successful summits of Everest — 21 — spoke earlier this year about how he has seen a decline in the amount of ice and snow cover on the mountain. In some places it has become bare rock, causing more dangerous rock falls. "Climbing is becoming more difficult," he said.

Whose climb is it anyway?

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Alan Arnette, a well-known mountaineer and blogger from Fort Collins, Colo., cares deeply about helping high-altitude climbers understand the need for personal responsibility. (Courtesy of Alan Arnette/The Coloradoan/Associated Press)

Sometimes the companies mounting these Everest expeditions have to decide what to do based on the strength of their climbers and how they are performing. But ultimately, those decisions come down to the personal responsibility of the individual climber, most mountaineers say, and part of that is knowing yourself.

Both Simonson and Arnette used the metaphor of knowing whether there is enough gas in a car's tank to get to the destination. While both men have scaled Everest, both have also turned around.

"For people who get that summit fever, and say 'I'm going to summit, I don't care, I've worked too hard and spent too much money and I'm going to summit, no matter what' — wow, not only is that unfair to them, but also to their teammates and to the Sherpas who perhaps are going to have to rescue them," Arnette told CBC News.

"There's a certain amount of personal responsibility that comes with this high-altitude climbing that I think is lost on some people," he added.