Himalayan glaciers have been the subject of intense debate amid growing concern that melting ice could imperil a wide swath of South Asia that relies on groundwater from the "Third Pole."
Scientists have struggled to improve their understanding of the glaciers' fate using satellite data and limited ground measurements, bumping up against the limits of the region's extreme topography and political barriers.
The picture that has emerged is complex, with wide variation among ice in the Himalayas, Hindu Kush and Tibetan Plateau. Studies suggest glaciers are stable or accumulating in the Karakoram Range on the Pakistan-China border. But in the eastern Himalayas and the Tibetan Plateau, they appear to be shrinking.
On supporting science journalism
If you're enjoying this article, consider supporting our award-winning journalism by subscribing. By purchasing a subscription you are helping to ensure the future of impactful stories about the discoveries and ideas shaping our world today.
That view is endorsed by a new National Academy of Sciences report, commissioned by U.S. intelligence agencies, that wrestles with the likely effect changes in Third Pole ice on South Asia's freshwater supplies and political relations.
But the analysis adds another wrinkle to the ongoing study of climate change in the Himalaya-Hindu Kush, arguing that changes in glacial runoff are unlikely to have major impacts on water supplies downstream over the next few decades.
Instead, the report argues, changes in Asia's powerful monsoon, increased snowmelt, growing reliance on groundwater, population trends and economic growth will have more powerful effects on the availability of fresh water.
It urges governments to better manage existing water resources and improve sanitation to hedge against future pressures on South Asia's water supply, including climate change.
Social changes needed to cope with climate change
"Social changes are going to be at least as important as changes in glacial contribution to river flows, and managing water resources," said Henry Vaux, the chairman of the committee that wrote the report and a professor emeritus of resource economics at the University of California, Berkeley.
"The situation is complicated. It doesn't lend itself to simple answers," he said. That complexity starts with the east-west divide in the condition of Himalayan ice.
Glaciers in the eastern and central parts of the region, fed by snow that falls during Asia's summer monsoon, are retreating at accelerating rates as the region warms -- though no faster than their counterparts around the world.
Glaciers in the western Himalayas, which depend on winter snow delivered by westerly winds from Europe, are stable. Some may even be advancing, the report says.
But the limited amount of data available on glacial accumulation and thaw, combined with the wide variation in the region's topography, make it hard to project how Himalayan ice will behave in coming decades.
Accelerating intensity of droughts and monsoons
At the same time, other effects of climate change, along with social and economic shifts, appear more likely than glacial retreat to affect availability of fresh water in the region's major water systems, including the Indus, Ganges and Brahmaputra.
In the Ganges, for example, there is evidence that "sizable and extensive overdraft" of groundwater will have an earlier, larger impact on water supplies than glacial melt, the report says. Projected increases in groundwater withdrawals for irrigation could eventually consume the entirety of the river's flow from November to March.
But climate change, driven by man-made emissions of greenhouse gases, aerosols and black carbon, is also likely to be an important influence, the report says, prompting changes in the timing and intensity of the annual monsoon and seasonal snowmelt.
"There are several reasons to think that climate change will make the dry season a little drier, and also increase the risk of flooding events," said Robert McDonald, a senior scientist at the Nature Conservancy and a member of the committee that wrote the report. "We tried to say, 'Look, climate change is coming -- and you better adapt.'"
Reprinted from Climatewire with permission from Environment & Energy Publishing, LLC. www.eenews.net, 202-628-6500