If you know much at all about Everest, you know that the Khumbu Icefall, where 16 Sherpa perished in an avalanche on April 18 while hauling gear up the mountain, is an incredibly dangerous place. Filled with crevasses and sitting under a massive serac, it has always been feared and revered by climbers—in fact Russell Brice, who runs outfitter Himalayan Experience, pulled his climbers off Everest in 2012, largely due to perilous conditions in the Icefall. But this year's unprecedented tragedy forces us to wonder: is anthropomorphic (man-made) climate change responsible?
"I've seen much bigger serac falls [than the one that occurred in the Khumbu Icefall on April 18]," says Everest veteran and photographer David Breashears, who was in Nepal at the time of the accident. "This is what glaciers do. They grow and shrink."
That said, Breashears is quite certain that climate change is transforming the Himalaya, and began a non-profit in 2007, called GlacierWorks, to document the changes being witnessed on Everest over decades. "Having this vivid imagery, it can incite the curiosity of the lay person," he said. "You can't refute that something has happened, it's left to the science to explain it."
Science can't say that the frequency and/or size of significant avalanches in the Himalayan region has grown over the past 100 or 50 years. But there is a significant amount that researchers have observed and tracked regarding the impact of climate change on the Himalayas, in general, and Mount Everest, specifically.
The International Centre for Integrated Mountain Development estimates that we’ve lost about a fifth of Himalayan glaciers in the past 30 years. The exact rate of melting, however, has been a contentious topic. The Intergovernmental Panel on Climate Change (IPCC) in a 2007 report forecasted that all the Himalayan glaciers would be history by 2035, but its findings were later found to be erroneous and the group retracted (much to the delight of climate deniers). The latest IPCC report, out last month, estimates that they will shrink by 45 percent by 2100, assuming the Earth's average surface temperature increases by 1.8 degrees Celsius (3.6 degrees Fahrenheit). (Some models predict an even higher heat increase, which would cut back glaciers closer to 70 percent in this century.)
Rising temperature is one factor (but not the only, as I'll describe below) that contributes to glacial melt. Insidiously, rising temperatures in low altitudes exacerbate warming in high altitudes. To learn how, I talked to Lonnie Thompson, paleoclimatologist at the Byrd Polar Research Center at Ohio State University, who studies ice cores, which he has collected at great heights in 58 different expeditions in 16 countries during his career. "Lonnie has spent more time at high altitude than [Reinhold] Messner and Conrad Anchor put together, " says photographer James Balog, the subject of the Oscar-nominated documentary Chasing Ice, told me.
Thompson has drilled for ice cores high in the Andes, Himalayas, and on Kilimanjaro. He studies the dust, isotopes, and chemicals found in the ice in order to understand the history of glaciers, ice caps, and ice fields. Rings in the ice also help describe climate history in similar way that tree rings do.
Thompson says rising sea surface temperatures moves moisture into the troposphere, which impacts high elevations. "When you intensify the hydrological cycle, which you do when you warm the earth, you get more heat moving up into the clouds... you're moving a lot of heat high into the troposphere and that [amplifies warming]. It certainly impacts the Himalayas and we can demonstrate that over the last 1,000 years looking at these ice cores. You have the maximum rate of warming happening at the highest elevations."
Adding to the warming is soot released from burning coal, diesel, wood, and dung throughout India and the wider the region. This black carbon is carried into the atmosphere, where it heats the air and is then deposited on snow and ice in the mountains. The coating decreases the snow's ability to reflect light (its albedo) and this amplifies melting. (Watch a NASA video that shows the movement of black carbon.)
This positive-feedback problem has been well-documented in the arctic, where the more sea ice is exposed, the less reflectivity the landmass has and the more ice melts. "You have similar things taking places in high elevation in these tropical ranges," says Thompson. "As the glaciers retreat, you get more darker areas, and the maximum rate of temperature rise is where you go from the land surface to the snow."
Unlike Thompson, however, most of us don't think about climate change in terms of isotherms and millibars of atmospheric pressure. We can't help but compare the way our favorite landscapes look from one year to the next, or how this winter compares to the last. Off course, that is a far too myopic approach.
Looking over decades, however, trends emerge and some changes start to gain permanency. Last May, Sudeep Thakuri, a researcher from the University of Milan told a meeting of the American Geophysical Union that, based on satellite and other image analysis, the snowline around Mount Everest rose 590 feet.
Thompson has collected some anecdotal evidence, as well. "In the Andes, we work with mountaineers and they tell us the ice has gotten more broken up at higher elevations. It's not as hard or secure for putting in anchors and this has increased the risk of climbing in those ranges," he says.