The deadly avalanche on Everest earlier this month wasn't technically an avalanche. It was an "ice release"—a collapse of a glacial mass known as a serac. Rather than getting swept up by a rush of powdery snow across a slope, the victims fell under the blunt force of house-sized ice blocks tumbling through the Khumbu Icefall, an unavoidable obstacle on the most popular route up Everest. The worst accident in the mountain's history has effectively ended the 2014 climbing season. And some see global warming as the key culprit.

"I am at Everest Basecamp right now and things are dire because of climate change," John All, a climber, scientist, and professor of geography at Western Kentucky University, told me by email. "The ice is melting at unprecedented rates and [that] greatly increases the risk to climbers."

"You could say [that] climate change closed Mt. Everest this year," he added.

Climbers had warily eyed the serac that collapsed on April 18 for years. In fact, a major expedition outfitter canceled its climbing season in 2012 because of it—a decision vividly reconstructed by Jon Krakauer in The New Yorker last week:

For many years, the most lucrative commercial guiding operation on Mt. Everest has been a company called Himalayan Experience, or Himex, which is owned by a New Zealand mountaineer named Russell Brice. In the spring of 2012, more than a month into the climbing season, he became increasingly worried about a bulge of glacial ice three hundred yards wide that was frozen tenuously to Everest’s West Shoulder, hanging like a massive sword of Damocles directly over the main route up the Nepal side of the mountain.

Ice frequently falls from this hanging glacier on the West Shoulder, and traversing the Icefall has always been treacherous. "Ice doctors" who install ladders and ropes in the area have long adjusted and readjusted the infrastructure in response to the collapses, big and small, that occur there on a daily basis. But experts believe these dangers are multiplying as average temperatures rise. In Krakauer's words, "the pronounced warming of the Himalayan climate in recent years has made the Icefall more unstable than ever, and there is still no way to predict when a serac is going to topple over."

Or take it from Tim Rippel, who runs Peak Freaks and was blogging from Base Camp last week:

As a professional member of the Canadian Avalanche Association I have my educated concerns. The mountain has been deteriorating rapidly the past three years due [to] global warming and the breakdown in the Khumbu ice-fall is dramatic, especially at the upper icefall. We need to learn more about what is going on up there. Each day we sit and listen to the groaning and crashing of the glacier.

The Icefall is a formation of the Khumbu glacier, which stretches between Everest and a neighboring peak called Lhotse. And, like others around the globe, this glacier is melting. (A caveat: Glaciers in the nearby Karakoram region, home to the towering K2, appear to be growing, according to the latest research.) The Khumbu glacier shifts by a few feet each day and has shrunk by more than half a mile in length (from 12,040 meters to 11,097 meters) over the past 50 years—though it's by no means the fastest-retreating glacier in the region. Base Camp, which sits on the glacier below the Icefall, has lost about 40 feet in elevation over the same time period, according to the glaciologist Mauri Pelto.