‘Most of the glaciers on Everest are covered in debris,’ says Professor Duncan Quincey, a glaciologist at the University of Leeds. ‘This layer of rock and detritus, which at the terminus can be the height of a room, can affect how the glaciers grow and retreat.’
Since 2003, a collaboration of researchers from the Universities of Aberystwyth, Sheffield and Hertfordshire have been improving data about debris-covered glaciers in the Himalayas. Debris-free (clean ice) glaciers grow forwards and melt backwards seasonally and are generally seeing a net retreat as the climate warms up. ‘Debris glaciers, on the other hand,’ says Quincey, ‘go up and down. But not a lot is known about how fast they will recede as the climate changes.’
Using a combination of measurements collected in the field and satellite images spanning the last 30 years, the team are working towards making computer-modelled predictions about how much meltwater the glaciers will provide in coming decades, and when the glaciers will vanish in the long-term. This information is vital for the 1.3 billion people who are sustained by the Himalayan meltwaters that nourish the Ganges, Indus, Brahmaputra, Yellow and Yangtze rivers.
Since the study began, they have found that behaviour varied with the thickness of the debris. ‘The general rule is that the thicker the debris, the more it insulates the ice,’ says Quincey, ‘or so we thought. Actually our recent measurements show that, maybe, once that debris has heated up enough, it becomes a heat reservoir that can warm the ice for longer even after the sun has gone down. So I think some of our data is going to show that what we’ve thought for a long time is not necessarily true.’
Rockslides and avalanches after the Nepal Earthquake have added material to a lot of the glaciers. ‘There have certainly been some big avalanches on to the top of the glacier surface,’ says Quincey. ‘Sometimes these avalanches can instigate a big reaction because they dump a lot of material on the top. The extra debris stops the ice from melting, but it also keeps the glacier quite thick and often, the thicker the ice, the faster it flows. It’s early days at the moment but we might see a dynamic reaction from the added debris in 12 or even 24 month’s time.’
Because of Everest’s obvious gravitas, the retreats of its glaciers are an important yardstick for measuring the rate of climate change. However, inaccuracy can be widely detrimental. In 2007, the IPCC (Intergovernmental Panel on Climate Change) report gave a false prediction that Himalayan glaciers would disappear by 2035. As it turned out, two figures were transposed from a report that read 2350. ‘That was their mistake,’ says Quincey, ‘but even the 2350 prediction from the original source was already questionable so maybe it shouldn't have gone in there at all. Nonetheless, it affected the validity of the report and was really damaging for our science.’
A thorough understanding of debris-covered glaciers will make it possible to calculate how quickly Everest’s glaciers are vanishing with better accuracy and help buffer the future impact on surrounding populations in India, Bangladesh, China, Nepal, Tibet and Pakistan.