By Navin Singh Khadka
Environment reporter, BBC News
Some recent findings seem to run counter to the view glaciers are retreating
A scientific debate has been triggered over the state of glaciers in the Himalayas.
Some recent findings seem to contradict claims that the glaciers are retreating rapidly. Some glaciers are even said to be advancing.
There are clear signs of glacial retreat and ice melt from other parts of the world, but few field studies have been carried out in the Himalayas.
Its glaciers too were widely believed to be receding fast.
The Intergovernmental Panel on Climate Change (IPCC) had said that Himalayan glaciers were receding faster than in any other part of the world.
The panel observed: "If the present rate continues, the likelihood of them disappearing by 2035 and perhaps sooner is very high if the Earth keeps warming at the current rate."
This report sparked concerns that there could be increased flooding in the short term, as glacial lakes suddenly overflowed.
In the longer term, major glacier-fed rivers, it was feared, would run dry, affecting millions in the region.
But some scientists claim that glaciers in the Himalayas are not retreating as fast as was believed. Others who have observed nearby mountain ranges even found that glaciers there were advancing.
Reports sparked concerns about increased flooding
Kenneth Hewitt, a glaciologist from Wilfrid Laurier University in Ontario, Canada, is one of these scientists. He has been doing field studies in Pakistan's Karakoram Mountains at the western reaches of the Himalayan range for the last 40 years.
Just back from that region, he told BBC News that he saw at least half a dozen glaciers that had been advancing since the last time he saw them - five years ago.
"Dozens of smaller, high altitude tributary glaciers have advanced including seven of Biafo Glacier and four of Panmah," he says.
"It means climate change is happening here too, but with different consequences."
Scientists have also described a phenomenon called glacial "surge". This is thought to be caused by melt water underneath the glacier lubricating its ground contact and causing it to move forward.
This is different from a real advance of a glacier, which is caused by an increase in the volume of ice.
"Rapid, surge-type advances have occurred in at least 17 glaciers since 1985, at least eight since 2000 [in the Karakoram]," says Dr Hewitt.
Out of date data?
In the western Himalayas, some scientists have also reported findings that conflict with the long-held view that glaciers are retreating.
The Indian government has issued a discussion paper based on these findings.
It says: "Himalayan glaciers, although shrinking in volume and constantly showing a retreating front, have not in any way exhibited... an abnormal annual retreat, of the order that some glaciers in Alaska and Greenland are reported to have done.
"It is premature to make a statement that glaciers in the Himalayas are retreating abnormally because of global warming."
Scientists say ground-level work is needed to validate findings
But noted Indian glaciologist Syed Iqbal Hasnain told BBC News that the data referred to in this paper are from the 1970s.
"I [was] asked to review the paper and clearly it does not reflect the current situation," he said.
"Things have changed in the last four decades."
Professor Hasnain has studied the Chhota Shigri glacier in Himachal Pradesh for four years and has found it to be retreating by 0.8m a year.
"(There is) no benchmark glacier in India which has been studied for many years," he says.
"Those that have been studied once or twice by some institutes are showing negative mass balance [or losing ice]."
He explained that precipitation and temperature were the main factors affecting whether glaciers retreat or advance.
All data, he says, show that precipitation is falling. And less precipitation means less accumulation of snow and ice.
The gradual disappearance of glaciers is causing huge concern.
Indian newspapers recently reported that some glaciers were retreating alarmingly quickly in Indian-administered Kashmir.
In China, glaciologists have also repeatedly warned of glaciers in Tibet retreating significantly.
But some experts argue that these conclusions often come from studies carried out in the snouts of glaciers, and that they do not represent the complete picture.
Richard Armstrong, a glaciologist with Colorado University in the US who also works for Nasa, says: "Retreat at the local point of the terminus doesn't describe what's going on in the entire glacier system that involves thousands of metres of elevation difference."
Having studied glaciers in the Nepalese Himalayas recently with the help of ground data and satellite imagery, Professor Armstrong said the upper air and surface station data indicated that above 5,400m there was no melting.
"It turns out [that] about half of the surface area of the glaciers that we studied in Nepal don't experience melt at any time of year."
Another scientist at the University of Nebraska at Omaha, Dr Michael Bishop, echoed Professor Armstrong's argument that the state of Himalayan glaciers was being overly generalised.
Dr Bishop has carried out glacier research funded by Nasa. He says: "Some people are making extrapolations based upon one or two glaciers.
"In the Himalayas, that can't be done because of the influence of topography and climate dynamics."
But Professor Hasnain says that those who criticise the finding that glaciers are retreating are often researchers who never go into the field and who rely too heavily on satellite images.
"When you are measuring from 35,000km (22,000 miles) above, the data cannot be accurate and so there needs to be [verification on the] ground," he told BBC News. "But people don't do that."
He says the argument that glaciers are not retreating remarkably is based on "flimsy ground".
Those who come to that conclusion, says Professor Hasnain, use Nasa's data.
"But [the US space agency] itself says that its own data is quite [different] from the ground data. That is why it is willing to work with us," he says.
Some researchers say satellite data is needed for a fuller picture
William Lau, who heads the atmospheric sciences branch at Nasa's Goddard Space Flight Center in Greenbelt, Maryland, says: "Nasa products are very useful in providing a broad picture of what is happening regarding the seasonal snow melt, and short term variations.
"[But] all satellite products have inherent uncertainties, and need to be calibrated and validated against ground observations.
Meanwhile, experts at the World Glacier Monitoring Service (WGMS), based in Zurich, Switzerland, say both in-situ measurements and remote sensing data are needed in order to get a complete image of glacier distribution and the changes throughout an entire mountain range.
Michael Zemp, a glaciologist at WGMS says: "There is a general centennial trend of glacier retreat from the moraines of the Little Ice Age (also) in the Himalayas."
But, he adds, "I do not know of any scientific study that supports a complete vanishing of [Himalayan] glaciers within this century."
The Kathmandu-based International Centre for Integrated Mountain Development has carried out some studies on glaciers.
It says that the general behaviour of the Himalayan glaciers is clear - overall they are currently in a state of rapid and substantial retreat.
"A few glaciers may be acting differently as a result of their different individual physical 'character'," it adds.
It appears that the impact of climate change in the region could be far more complicated than previously thought.
And despite varying observations, experts do agree on one thing: there has to be an increased level of scientific observation to record the changes in Himalayan glaciers and make reliable predictions.
The absence of this data could make the issue of Himalayan glaciers a knotty one during the international climate negotiations in Copenhagen in December.