High-Himalayan glaciers thinning
This fascinating image shows a variety of textures formed in ice of the Khumbu glacier in Nepal; one of the main glaciers that drain the Everest area and a stop on the most common route to the summit.
I’m sharing this image to illustrate some new scientific work on glaciers like this one in the highest parts of the Himalaya. Ponder this question to go with this photo; how do you determine whether a glacier at this altitude is shrinking or growing?
Many glaciers at lower elevations are retreating; the position they stop at can be measured year after year, and they’re mostly retreating up valleys around the world. High in mountain ranges and far away from the terminus however, figuring out what a glacier is doing is difficult. Glaciers move down valleys and can stretch, crack, and bend as they do. Snow will pile up on glaciers in the winter and, as you see here, it can form some fascinating structures when it melts/evaporates in the summer.
If you tried to measure the thickness of this glacier from the air, perhaps by bouncing lasers off it to measure the height, features like this would make it very difficult to get an accurate estimate. A few glaciers may be well tracked and people on the ground could actively measure the thickness, but most glaciers in the high-Himalaya are so remote that people aren’t going to regularly make that measurement.
These glaciers are a major part of feeding the watersheds for the cities below, so monitoring their health is important. Some recently presented work by a researcher at the Chinese Academy of Sciences’ Institute of Tibetan Plateau Research strongly suggests these glaciers may be in more trouble than we think.
If a glacier at these elevations is growing or even steady, it will add some snow at its summit every year and it will lose some mass at its base every year. At the highest parts of the glacier therefore, a new band of snow should be produced every year. That band of snow will contain remnants of other things happening in the atmosphere; volcanic ash, dust, or even manmade components.
There are 2 easily measured horizons that should show up in these glaciers. From 1952 to 1963, aerial nuclear weapons tests produced radioactive tritium that would be stored in the ice layers, and in 1986, the Chernobyl nuclear disaster in the Ukraine produced a similar radioactive spike. If a scientist takes a core through a stable glacier in the Himalayas today and works downwards, those years should be easily recognized by the radioactive elements.
These researchers sampled several glaciers that were previously unmonitored and looked for those years. In one glacier, the Guoqu glacier in Central Tibet, the bomb test signal shows up but the glacier does not include the Chernobyl signal or any volcanic eruptions following 1982. Other measures, such as mercury content, also only track up to the early 1980’s, suggesting that this glacier has not added significant mass since the early 1980s, a period of 3 decades. If later years were added, they have since ablated away.
Another glacier in southern Tibet, the Lanong glacier, is in even worse shape. It contains neither the Chernobyl signal nor the atmospheric weapons test signal. That glacier has not been able to add mass at a normal rate for years; any ice added since the 1950s, and perhaps even earlier, has melted or ablated away.
Many of these glaciers are unmonitored and since it is difficult to measure their thicknesses using any other technique people haven’t believed they could be in this bad of shape, but decades of mass loss in the investigated locations is a very disturbing trend. These results suggest that the glaciers of the high Himalayas, which supply water to hundreds of millions of people, are suffering the effects of a changing climate even worse than was expected. This type of sampling clearly needs to happen on a larger scale to better assess the health of these systems.
-JBB
Image credit: Robert Nunn http://www.flickr.com/photos/robnunn/5312171842/
Press report: http://tibet.net/2013/09/18/tibetan-glaciers-are-shrinking-at-their-summits/
(Source: facebook.com)
