for National Geographic News
Some glaciers in Pakistan's Upper Indus River Basin appear to be growing, and a new study suggests that global warming is the cause.
The glacial growth bucks a global trend of shrinking ice fields (photos: melting glaciers) and may shed light on the regionally varying effects of Earth's changing climate.
Meteorological data compiled over the past century show that winter temperatures have been rising in parts of the Western Himalaya, Karakoram, and Hindu Kush mountain ranges (map of Pakistan).
But the region's winter snowfall, which feeds the glaciers, has been increasing. And average summer temperatures, which melt snow and glaciers, have been dropping.
"One of the surprising results we found was a downward trend in summer temperatures," said David Archer, study co-author and a hydrologist at Newcastle University in the United Kingdom.
"That seems to be at odds with what people would expect, given the news about glaciers melting in the Eastern Himalaya." (Read "Himalaya Ice-Melt Threat Monitored in Nepal" [March 2006].)
The combination of reduced summer melt and more winter snowfall could account for glacial growth, according to work to be published by Archer and colleagues in an upcoming issue of the American Meteorological Society's Journal of Climate.
The new study compiled thousands of pages of climatic data that were collected at weather stations during the past century.
The records even include 19th-century documents taken from British archives that predate the creation of modern Pakistan in 1947.
In addition to explaining growing glaciers, the combined data could help scientists predict and manage critical meltwater resources that support about 50 million Pakistani people.
Temperatures and precipitation are the main drivers of seasonal water runoff into the Indus River and its tributaries, which nurture Pakistan's largely agricultural economy.
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