Image credit: bongo vongo/Flickr
After the Arctic and Antarctica, the snow and glaciers of the Himalayas are the largest store of water on the planet. When the ice of this "Third Pole" melts each spring, it supplies the largest rivers in Asia—including the Ganges, Indus, Brahmaputra, Mekong, Yellow, and Yangtze rivers—with a surge of fresh water that is desperately needed to support the huge populations lining their banks.
This region, however, is warming rapidly—nearly twice as fast as the rest of the world. Though greenhouse gasses have traditionally been blamed for the melting ice of the Tibetan Plateau, new research suggests another factor may be equally significant and could be the key for preserving this vital resource.A study co-authored by NASA's Goddard Institute for Space Studies and the Chinese Academy of Sciences has identified black carbon, the dark and dangerous component in the soot, as a key factor in warming in the Himalayas. "During the last 20 years," explained Junji Cao, a researcher from the Chinese Academy of Sciences, "the black soot concentration has increased two- to three-fold relative to its concentration in 1975."
Black carbon is produced by diesel engines, coal-fired power plants, industrial processes, and outdoor cooking stoves in India and China, and is pulled into the Himalayas by circulating air currents. The dark soot absorbs solar radiation, warming the air that crashes against the foothills of the Himalayas and propels it into higher elevations. This "heat pump" effect is thought to be the source of the region's rapid warming.
William Lau, a researcher at the Goddard Institute, explained that, "it's not difficult to conclude that greenhouse gases are not the sole agents of change in this region. There's a localized phenomenon at play." He also commented:
The phenomenon changes the timing and intensity of the monsoon, effectively transferring heat from the low-lying lands over the subcontinent to the atmosphere over the Tibetan Plateau, which in turn warms the high-altitude land surface and hastens glacial retreat.
And the retreat is hasty indeed. Tandong Yao, director of the Chinese Academy's Institute of Tibetan Plateau Research, said that, "fifty percent of the glaciers were retreating from 1950 to 1980 in the Tibetan region; that rose to 95 percent in the early 21st century." At current rates of melting, many glaciers are expected to be completely gone by mid-century.
All Carbon is not Equal
Researchers pointed out that, in this case, all carbon is not the same. Organic carbon, produced by wood burning and other processes, is not as dark and thus, does not have the same warming effect as an aerosol.
In fact, black carbon is unique among aerosols in its relationship with solar radiation. Most reflect sunlight which creates a cooling effect.
An Opportunity to Save the Glaciers
In one sense, this discovery casts a dark shadow on the prospect of glacier survival in the Himalayas. In addition to greenhouse gas emissions—something we are having enough trouble getting a handle on—these essential ice flows are threatened by a pollution whose source is ubiquitous in South Asia.
However, black soot also offers an opportunity to save, or at least slow, glacier melting on the Tibetan Plateau. Black carbon particles have a shorted lifespan in the atmosphere than greenhouse gasses, meaning a reduction in emissions could have a substantial and rapid impact.
Whether that is accomplished with filters, cleaner diesel engines, or some other process remains to be seen but, as William Lau said, these finding show that "we need to add another topic to the climate dialogue."
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