Scientists scurry to figure out the status of glaciers on the roof of the world
The Himalayas have gotten hot.
Mercury in this mountainous region has been climbing, with more warming there in recent decades than in most other places on Earth.
“Temperatures are rising fast at high elevations,” says David Molden, director general of the International Centre for Integrated Mountain Development in Kathmandu, Nepal.
But the heat-up isn’t limited to temperatures. Scientific attention has also intensified, as researchers worried about the fate of glacial ice take a closer look at this remote, inhospitable terrain — sometimes called “the roof of the world.”
In 2007 the Intergovernmental Panel on Climate Change released a report cautioning that “glaciers in the Himalaya are receding faster than in any other part of the world … and, if the present rate continues, the likelihood of them disappearing by the year 2035 and perhaps sooner is very high.”
That claim has since been retracted. Though it wasn’t based on even the little bit of peer-reviewed data that existed, the commotion surrounding it highlighted the need for new research. Only a handful of Himalayan glaciers were monitored on the ground for mass changes during the 20th century. And when the IPCC report was released, no one had measured and published the mass of any Himalayan glacier since the year 2000.
Since the embarrassing fumble, scientists have been working at a fever pitch to fill in the knowledge gap. Treks into Asia for long-overdue checkups and analyses of evidence from satellites now provide a window into what’s happening in the Himalayas — and it’s not what many scientists had expected.
Big questions remain, but the emerging picture discredits not only the initial IPCC proclamation, but also the idea that all the glaciers in Asia’s high mountains are responding to climate change in a similar way. Opposite ends of the mountain chain have their own neighborhood feels, researchers have realized. Glaciers have sweated and suffered in the east, some more so than others. But many in the west have defied rising temperatures, gaining mass in recent years.
“People assume something that’s happening on one end of the Himalayas affects the entire area,” says Mark Williams, a hydrologist at the University of Colorado Boulder. “That’s simply not true.”
An uptick in interest in the Himalayas has also helped overturn unfounded ideas about how much water melting glaciers contribute to Asia’s rivers. Worries that melting could threaten the long-term health of the large rivers crisscrossing India and China haven’t held up to new research.
Like glaciers elsewhere in the world, Himalayan ice caps owe their existence to a delicate hydrological balance. Avalanches from above and precipitation freezing on top of the ice add mass. Sublimation from the surface removes mass. So does melt at a glacier’s leading edge; such melting crests during late summer and early autumn and sends water downslope.
Weather patterns controlling this balance change dramatically throughout the high peaks of Asia. The vast mountain system sprawls thousands of kilometers across Asia’s midsection, touching the wet subtropics of Bhutan in the east and the dry steppes of Afghanistan in the west.
Ice in the west, near Pakistan and Afghanistan, has proved to be surprisingly healthy in recent years. Satellites launched around the beginning of the millennium are seeing signs of growth in the craggy peaks of the Karakorams, where ice caps are fed by year-round snowfall. The leading edges of more than half of the 42 glaciers monitored there from 2000 to 2008 held steady or crept outward, researchers reported last year in Nature Geoscience.
Work from a team in France confirms a slight mass gain overall in the Karakoram range, which extends for about 500 kilometers. Instead of tracing glaciers’ leading edges — which can be deceiving — the researchers worked out changes in mass. They relied on a European satellite that in 2008 mapped the three-dimensional contours of about 5,600 square kilometers of ice.
Compared with a similar map for 2000, made possible by a NASA shuttle mission, the ice was thicker by an average of about 11 centimeters per year, the researchers reported in the May issue of Nature Geoscience. Some glaciers at lower altitudes lost ice, but overall the region gained an estimated 110 kilograms of ice per square meter per year (with large uncertainties).
“This is direct evidence that the glaciers in the area have behaved quite well,” says study coauthor Etienne Berthier, a hydrologist at the University of Toulouse.
Glaciologist Kenneth Hewitt saw signs of this behavior more than a decade ago. In the 1990s during a visit to K2, infamous among climbers for being particularly deadly, Hewitt found that the leading edge of the Bualtar Glacier there had crept forward. Ice at the glacier’s high-altitude end had thickened as well. From 1997 to 2002, a dozen other glaciers showed hints of expansion — most of them at high altitudes, more than 7 kilometers above sea level.
Convincing the scientific community that this was a trend proved difficult. Many of these advancing glaciers had been on the retreat up until the 1980s. In fact, most glaciers around the world had been on the retreat during the 20th century.
“This change appeared very suddenly … and most people wouldn’t believe it at first,” says Hewitt, a professor emeritus at the Wilfrid Laurier University in Waterloo, Canada, who reported his observations in 2005 in Mountain Research and Development.
Though the Karakoram weight gain is now accepted, why the growth spurt is occurring — and whether it will last — remains a mystery. Rain gauges in valleys far below the glaciers have measured an increase in precipitation in recent years. Changing wind patterns could be bringing in more moisture. Or a spate of strangely cool summers in the valleys could be cutting back on melting at the edges.
But there aren’t exactly a plethora of meteorological monitoring stations at higher altitudes where the prospering glaciers live, leaving predictions for the future murky. It’s possible that the ice is simply softening and surging downward, allowing for a temporary increase in mass at the top, says Hewitt. That kind of behavior, common in Alaska and Iceland, typically doesn’t last very long, which means the glaciers could soon start to shrink again.
Recent growth of glaciers in the Karakoram stands in stark contrast with pronounced shrinkage elsewhere in the Himalayas, where behavior is closer to scientific expectations. Several lines of new evidence confirm an ongoing trend of ice loss in Tibet, Nepal and other countries to the east. There, glacier edges have shed ice faster than it can be replaced.
The same study that revealed expanding edges on Karakoram’s glaciers also spotted widespread contractions in areas where glaciers are nourished mostly by summer monsoons instead of year-round snow. Between 2000 and 2008, more than 65 percent of monsoon-fed glaciers retreated, though the exact proportion varied from place to place.
Dirty ice seems to have fared better on the whole. Ice caps littered with debris closer to the center of the Himalayas were more likely to hold the line than their cleaner cousins on parts of the Tibetan Plateau, where around 80 percent of glaciers shrank. A coating of fallen rocks may insulate the ice from warm air.
Recent trips to low-lying glaciers have confirmed changes in mass at a few sites to the east of the Karakoram. Koji Fujita and Takayuki Nuimura of Japan’s Nagoya University stopped by three glaciers in Nepal. Using GPS devices to map the contours of the ice, the researchers found that ice had disappeared at each site. Melting had accelerated since the 1990s at two of the glaciers, which are “doomed to disappear,” the researchers reported last year in the Proceedings of the National Academy of Sciences.
But contrary to the IPCC’s initial claim, glaciers to the east don’t seem to be “receding faster than in any other part of the world,” says glaciologist Tobias Bolch of the University of Zurich. His measurements show shrinkage at a rate more or less comparable to elsewhere. “Overall, the volume changes of the glaciers are within the average of glaciers across the globe,” he says.
Bolch recently pieced together the longest history of a group of Himalayan glaciers ever attempted, thanks to a cache of declassified photos taken by U.S. spy satellites. Started in 1959, the CORONA project kept tabs on Russia and China. Fortunately for the cause of science, the satellites also snapped some stellar shots of glaciers — in stereovision that reveals the 3-D shape of the ice.
Compare these data with modern satellite measurements, as Bolch did, and you can see how the massive glaciers near Mount Everest have changed. Ten ice caps in this area of the eastern Himalayas all thinned between 1970 and 2007, Bolch and colleagues reported last year in The Cryosphere.
Like many researchers, Bolch shies away from predicting the glaciers’ ultimate fates. He merely points out that not all the eastern ice giants will vanish in the coming decades. Many may survive for a century or more.
As for how much ice is being lost in the whole of the Himalayas, including the Karakoram region, scientists don’t yet have a clear picture.
One attempted estimate looked at changes in the area covered by glaciers using old hand-drawn topographic maps, recent satellite images and extrapolations from on-the-ground measurements. In a paper published posthumously in 2010, Mark Dyurgerov reported data suggesting that Asia’s high mountains had been losing an average of 55 billion metric tons of ice every year from 2002 to 2006. That’s enough ice to sculpt about 57,000 life-size replicas of the Empire State Building.
But the small number of glaciers measured in Dyurgerov’s study may not be representative of the tens of thousands of other glaciers in the Himalayas.
“Data on the ground comes from glaciers that are easy to get to. They’re at low elevations, and they’re small,” says Richard Armstrong, a glaciologist at the National Snow and Ice Data Center in Boulder. “Those are likely the ones to be melting the fastest.”
Dyurgerov’s estimate has been challenged by a relatively new technique for monitoring huge areas of ice from space. Reporting in Nature in February, researchers from the University of Colorado Boulder describe measurements from a pair of satellites called GRACE that sense the gravitational pull of ice’s mass (SN: 1/4/03, p. 6).
Nicknamed Tom and Jerry, the spacecraft chase each other in orbit like their cat and mouse namesakes. Areas of higher or lower gravity push and pull the satellites apart. Large changes in ice over time show up as noticeable gravitational fluctuations.
Fluctuations from 2003 to 2010 seemed to indicate that the Himalayas had lost only about 5 billion metric tons of ice per year, much less than the 55 billion estimate.
Whether data from this newfangled dousing rod will prove reliable remains to be seen. Critics point out that the twin spacecraft detect all of the gravity variations, not just those due to ice. Groundwater movement could muddy the data.
Greg Greenwood, executive director of the Mountain Research Initiative in Bern, Switzerland, wouldn’t say the new data are cause for celebration. “We still should be concerned because many huge reservoirs of water are wasting away at a significant rate,” he says.
Greenwood worries that once shrinking glaciers are gone, Asia will miss the seasonal meltwater they provide. But recent data suggest that not all nations should share that concern. While acquainting themselves with the region’s glaciers, scientists have picked up a better understanding of how water flows into and out of the ice. Patterns that again pit east versus west have offered good news for some countries.
Glaciers in the Himalayas are often called Asia’s water towers. They store more frozen water than any place on the planet save the titanic ice sheets in the polar regions. Summer melt from Himalayan glaciers streams down to low altitudes, where the rivers fed by the melt offer a source of water for billions of people.
Scientists once thought that glaciers provided most of the summer flow into the rivers of East Asia. Up to 70 percent of water in the Ganges and half or more of that in other major rivers started off as glacial ice in the Himalayas, a 2005 review in Nature claimed. In this view, vanishing glaciers would deprive these rivers of an important seasonal water pulse.
But such estimates have now been questioned by Walter Immerzeel, a hydrologist at Utrecht University in the Netherlands. His simulations, based on recent on-the-ground measurements of rainfall and water streaming down from mountains, as well as satellite measurements of snow cover, show that only 9 percent of the Ganges comes from the mountains. China’s Yangtze and Yellow rivers carry an even smaller portion of mountain water, Immerzeel and colleagues reported in 2010 in Science.
These estimates include both water melting from glaciers and precipitation that never freezes onto the glaciers. When snow melt is removed from the figures, the glacial contribution is left at around 3 percent for the Ganges.
“We now know that glacial melt is a very small component of the water supply in those regions,” Immerzeel says.
Calculations by Armstrong also suggest a 2 or 3 percent contribution to the Ganges from glaciers in the east Himalayas.
For all their heft, the ice mounds simply can’t compete with the water delivered by monsoons. Every year, the seasonal rains dump tremendous amounts of water into the river basins of India and China.
If all the glaciers disappeared overnight, the rains would still fall. Without glacial contributions late in the summer and fall, river flows might peak a little earlier in the year. That could affect crops that need water later, but little work has been done to explore this scenario.
The situation is different in arid Afghanistan and Pakistan, where little liquid falls from the sky. In those countries, the traditional wisdom about glacial runoff being important for rivers holds true. Melt from mountain snow and from glaciers makes up more of the Indus River than precipitation that enters the river downstream at low altitudes, Immerzeel’s calculations showed.
For the Indus — and for the sprawling irrigation systems that depend on it — the growth of glaciers in the Karakoram could be a double-edged sword. In the long run, it’s good news. “We can hope that the Karakoram glaciers will continue to put water into the rivers for a long time,” says Berthier.
But the growing glaciers’ contributions to the river will probably be smaller in the short run.
Better measurements will be needed to fully tease out the interplay of rain, snow and ice so crucial for Asia’s future. Those data could be coming soon. The U.S. intelligence community recently commissioned a study to assess the impact of glaciers on Asia’s water security. Other entities with similar concerns, including the U.S. Agency for International Development, have put money into new monitoring efforts. Closer to the source, China and India have launched their own projects.
Everyone is hoping the next IPCC report, the first portion of which is due out in 2013, will offer a clearer portrait of melting glaciers and river water sources.
“The Himalayas seem to have suddenly become quite popular,” Armstrong says. “European glaciers have been studied for decades. Now Asia’s finally getting up to speed.”
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