[Article] Some Glaciers Growing Due to Climate Change, Study Suggests
September 5, 2009 Leave a comment
for National Geographic News
September 11, 2006
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.
Fed by snowmelt and glacial runoff, a massive dam and irrigation system in the Indus Basin supplies water to farmlands that cover about 65,640 square miles (170,000 square kilometers).
The waters also drive hydroelectric power facilities at the Mangla and Tarbela Dams.
Hayley Fowler is lead author of the study and a senior research associate with Newcastle University’s School of Civil Engineering and Geosciences.
“Our research suggests we could be able to predict in advance the volume of summer runoff, which is very useful in planning ahead for water resources and also the output from the dams,” Fowler said in a statement.
About a third of the annual runoff comes from glaciers in the high mountain peaks and is regulated largely by summer temperatures.
The latest study suggests that a 1.8°F (1°C) drop in mean summer temperature since 1961 has cut that glacial melt by 20 percent.
But winter snowfall drives the remaining two-thirds of annual runoff. This volume has been increasing as snowfall totals rise.
The data also reveal another climatic oddity—a change in the basin’s diurnal temperature range, or the span between daytime high and nighttime low temperatures for a given day.
“There’s a large increase in the diurnal temperature range observed in all seasons and in all the annual data sets,” Archer said.
“In most parts of the world there’s been a decrease in diurnal temperature change, and this is what’s being predicted by global climate-change models.”
All together, the area’s regional variations are at odds with most glaciated regions worldwide, including the Eastern Himalaya, where glaciers have been shrinking significantly.
Lonnie Thompson, a paleoclimatologist and glacier expert at Ohio State University in Columbus, thinks the latest findings might be a short-term trend only.
“My guess is that the glaciers in [Haley and Fowler’s] area of study might find short-term benefit where increased winter snowfall outweighs summer melt,” Thompson said.
“[But] it’s likely these glaciers will follow the same pattern of those in Sweden and Norway, which were growing until 1999 due to increasing winter snowfall even as temperatures rose.
“However, since 1999 these same glaciers are now retreating.
“The balance of glaciers globally shows retreat and even acceleration in the rate of retreat,” Thompson stressed. (Related news: “Greenland Glaciers Losing Ice Much Faster, Study Says” [February 2006].)
It may take many years to understand climate change’s lasting effects on Pakistan’s glaciers.
But Archer hopes for much more immediate payoff from the recently published climate data.
“We’re not entirely sure what long-term climate change trends will do,” he said. “But in the meantime, [water forecasting] is a really important, immediate, practical issue.”
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