“The biggest result here is that the glaciers in the basin, we find them to be more sensitive to temperature than anyone expected before,” says Shea.
The glaciers of the Dudh Koshi basin cover more than 150 square miles in area. To study them, the researchers used a glacier model and fired it with different climate change scenarios based on emissions pathways used by the Intergovernmental Panel on Climate Change. And they found that in one extreme model run, glacial loss by the year 2100 could be 99 percent. However, there were a range of estimates, and the low end number for glacial losses was 70 percent – still quite a large decrease.
The more moderate emissions scenario used in the study, technically dubbed RCP4.5, is one in which the world actually undertakes significant greenhouse gas reductions over the course of this century. “Even if we take measures now, we see it still declining,” says Shea.
Glaciers elsewhere in the Himalayas, Shea cautions, would not necessarily behave in the same way, and so we shouldn’t assume they’re as vulnerable as those around Everest.
The chief losses of glaciers would not occur near the peak of Everest, some 8,850 meters into the air. Rather, the greatest loss would be at elevations between 5,000 and 6,000 meters, the study found, which is where most of the mountain’s glaciers are actually located. Higher up, there is actually less ice to be found, and it is not expected to decline in the same way.
The result persisted even in climate model scenarios that included more regional precipitation, a factor that can help add mass to glaciers (especially if it comes in the form of snow). “Expected increases in temperature will result in sustained mass losses that are only partially offset by increases in precipitation,” the study finds.
The research also suggests that this melting process could, on occasion, lead to sudden large discharges of water from gigantic melt lakes atop the glaciers — not good news for a region that just suffered from a devastating earthquake.
In an accompanying blog post, Shea notes that the glacial melt isn’t just the result of rising temperatures in the model. There’s another factor. A trend of overall warming “raises the elevation of the freezing level, which has two secondary effects: the area exposed to melt will increase, and the amount of snow accumulation will decrease,” he writes.
In the past, broader claims about changes to glaciers in the Himalayan region have been a source of major controversy.
In a 2007 report, the U.N.’s Intergovernmental Panel on Climate Change alarmingly stated that the mountain glaciers of the Himalayan region could be gone by the year 2035. But the statement turned out to be in error, leading to an IPCC acknowledgement of inadequate vetting of the material and many criticisms of the climate science body — as well as the dubbing of the incident “Glaciergate.” (The report section in question now includes an errata noting the problematic claim.)
As with all scientific studies, there are limits and considerable uncertainties to the current projections about glaciers in the Everest region. In essence, what the researchers have found is likely based on the best available science — but science is always getting better.
“The model we’re using is a tool, and there are more complex ways of modeling the glaciers, but we don’t have that information yet,” Shea says. “But this is the tool we’re using, and what that tool is showing is that the glaciers are quite sensitive.”