NEW DELHI - Climbing to the roof of the world is becoming less predictable and possibly more dangerous, scientists say, as climate change brings warmer temperatures that may eat through the ice and snow on Mount Everest.
Nepal was left reeling when a sudden ice avalanche slammed down onto a group of Sherpa guides on Friday and killed 16 in the deadliest single disaster on Everest. While it is impossible to link any single event to long-term changes in the global climate, scientists say the future will likely hold more such dangers in high-altitude regions.
Avalanches of snow, rock or ice could increase. Climbing and trekking terrains would become unsteady. Glaciers may be more unpredictable. Storms will become more erratic, and the Himalayas in particular could see more snow as warming oceans send more moisture into the air for the annual Indian monsoon that showers the 2,400-kilometer (1,500-mile) mountain range.
Friday's disaster occurred at the Khumbu Icefall, long recognized as one of Everest's most dangerous spots, as the edge of the slow-moving glacier is known to crack, cave and send huge chunks of ice tumbling without warning.
"It's Mother Nature who calls the shots," Tim Rippel, an expedition leader, said in a blog post from Everest base camp as many of the 400 Sherpa guides were leaving, demanding better government compensation for the high risks they take in helping climbing companies ferry rich tourists up the peak. "The mountain has been deteriorating rapidly in the past three years due to global warming, and the breakdown in the Khumbu Icefall is dramatic," he said. "We need to learn more about what is going on up there."
There is nothing to prove the icefall was behaving unusually on Friday. But scientists say mountaineers should assume that everything is now in flux.
What makes the situation so risky, scientists say, is the uncertainty itself. While scientists are sure things are changing, they're not entirely sure how. Much of the evidence is anecdotal, and there isn't enough data or decades of scientific observation to draw solid conclusions. Rigorous glacier studies have only begun in the Himalayas in the last decade, and no one is studying snow patterns on a large scale, Nepalese glaciologist Rijan Bhakta Kayastha at Kathmandu University said.
Meanwhile, as global temperatures have gone up 0.75 degrees C (1.4 degrees F) in the last century, according to the International Panel on Climate Change, studies show the Himalayas warming at a rate up to three times as high.
"You can be sure that if the climate is changing -- and it is - then glaciers are changing and the danger is shifting," said U.S. hydrologist Jeff Kargel of the University of Arizona who is leading a global project to measure and map the tens of thousands of Himalayan glaciers through satellite data. "It doesn't necessarily mean it's getting worse, it just means you don't know."
Kargel said population in the vicinity also plays a role. "The more people you have living or trekking in the mountains in seemingly blind disregard for a changing hazard environment, the more catastrophes you'll have," he said Wednesday in a telephone interview.
High-altitude mountain climbing has always been inherently risky - more so as more people take those risks. Hundreds have died attempting to summit Everest from avalanches or rock falls, or from hypothermia or altitude sickness. The Sherpas who died on Friday were some of today's most skilled Everest climbers, underlining the fact that experience is no guarantee of safety, even if better gear and oxygen-breathing equipment have helped reduce some dangers.
But the high number of unskilled climbers going up Everest has alarmed seasoned mountaineers.
"For many attempting Everest, it is not for love of the mountains, but for the prestige," said Col. H.S. Chauhan, president of the Indian Mountaineering Foundation.
More than 4,000 climbers have scaled the 29,035-foot summit since 1953, when it was first conquered by New Zealand climber Edmund Hillary and Sherpa Tenzing Norgay. The numbers have skyrocketed in recent years along with guided expeditions charging up to $75,000 to help even novice trekkers reach the peak. More than 800 climbers tried during the 2013 spring season, and there were likely at least as many signed up this year.
But some, spooked by Friday's disaster, have already packed up and left.
The legendary Apa Sherpa, who holds the record in summiting Everest 21 times, has been warning about rising risks from climate change for years. When he first summited the mountain in 1990, the trails were covered in thick layers of packed ice and snow. "Now, the trail is full of bare and exposed rock," he said, making it harder for climbers to gain footholds with their spiky metal crampons meant for digging into ice.
"The danger level has significantly risen for climbers," said Apa, 53, who now lives in Draper, Utah, and last conquered Everest in 2011.
Newly exposed rubble and rock can also cascade in rock avalanches - as now happens on the Eiger in the Swiss Alps during summertime.
Meanwhile, heavier snow storms would lead to more snow accumulating, raising avalanche risks. Shifting wind patterns may also affect how snow and ice behave. Glacier movement could change, and an increase in melt water trickling down could cause a glacier to move more quickly.
"Changes in snow and ice are going to strongly influence the stability of snow on a slope and the possibility of an avalanche," said American glaciologist Tad Pfeffer with the Institute of Arctic and Alpine Research at the University of Colorado, Boulder.
"The danger in mountaineering is a combination of what's going on in the natural world and what the climbers are doing," Pfeffer said. "People will get in trouble if they rely on what they knew in the past. They have to have their eyes open and not go somewhere or do something simply because it worked out five years earlier."