Four people have been found dead in tents on Mount Everest, bringing the death toll for this climbing season to 10.
Nepalese Sherpas discovered the bodies in tents at Camp IV, the camp closest to the summit of the world's tallest mountain. It stands at an altitude of more than 26,000 feet, near the so-called death zone where there is very little oxygen.
Mingma Sherpa of the Seven Summits Trek group, the company the Sherpas worked for, confirmed the news to The Associated Press and Reuters on Wednesday.
The identities of the deceased climbers have not been released, though The Himalayan Times reported that two were Nepalese and two were foreigners. It said one was a woman.
While the cause of death is not yet known, the fact that they apparently died inside tents led seasoned Everest blogger Alan Arnette to speculate: "It is most likely they died from carbon monoxide poisoning by using their stoves in the tent without proper ventilation."
The Times said the Sherpas found the climbers while trying to recover the body of "49-year-old Slovakian solo climber Vladimir Strba who died at Camp IV on Sunday afternoon."
Everest is particularly busy at the moment because the Nepalese government has issued a record 371 permits for foreign climbers, the AP notes.
Deaths on Everest are tragically common — at least 200 people have been killed attempting to climb it since 1920, the BBC reported. "However, the numbers of people attempting the climb have also skyrocketed since 1990, when the Nepalese government withdrew restrictions on how many teams were allowed on to the mountain — which means the percentage of climbers who die has actually dropped."
British Everest expedition leader Tim Mosedale wrote in a recent Facebook post that the increasing number of climbers has led to more guides who are less-experienced:
"Over the years there's been a huge dilution in the cumulative experience of staff whilst at the same time there's been a net increase in inexperienced or poor expedition providers. When you combine this with a decline in the amount of experience of the clients who are accepted on board it's a worrying equation."
Major causes of death on Everest include "exhaustion, exposure, frostbite, falls and altitude sickness," Reuters reported. "But the biggest killer in recent years has been avalanches."
Avalanches in 2014 and 2015 meant that many people who intended to climb the mountain had to delay their attempt, the AP reported, which may have contributed to the higher number of climbers this year.
In addition to the deaths of the four newly discovered climbers and Strba, five others have died this season: Ravi Kuma of India, Roland Yearwood of Alabama, Francesco Enrico Marchetti of Australia, Min Bahahur Sherchan of Nepal and Ueli Steck of Switzerland.
Despite the grim news, there's also been some inspiring developments on Everest this season. The BBC reports two new possible speed records:
"[A] 29-year-old Spaniard is being hailed as having reached the summit in the fastest-ever time, without rope or extra oxygen.
"Kilian Jornet reached the top, from the Tibetan side, in just 26 hours, his team said yesterday. The record cannot be verified until he returns.
"An Indian woman, Anshu Jamsenpa, is also believed to have set the new woman's record for the fastest double ascent, having climbed the mountain twice in one week."