Meltwater from Asia's peaks is much less than previously estimated, but lead scientist says the loss of ice caps and glaciers around the world remains a serious concern
The discovery has stunned scientists, who had believed that around 50bn tonnes of meltwater were being shed each year and not being replaced by new snowfall.
The study is the first to survey all the world's icecaps and glaciers and was made possible by the use of satellite data. Overall, the contribution of melting ice outside the two largest caps – Greenland and Antarctica – is much less than previously estimated, with the lack of ice loss in the Himalayas and the other high peaks of Asia responsible for most of the discrepancy.
Bristol University glaciologist Prof Jonathan Bamber, who was not part of the research team, said: "The very unexpected result was the negligible mass loss from high mountain Asia, which is not significantly different from zero."
The melting of Himalayan glaciers caused controversy in 2009 when a report from the UN's Intergovernmental Panel on Climate Changemistakenly stated that they would disappear by 2035, instead of 2350. However, the scientist who led the new work is clear that while greater uncertainty has been discovered in Asia's highest mountains, the melting of ice caps and glaciers around the world remains a serious concern.
"Our results and those of everyone else show we are losing a huge amount of water into the oceans every year," said Prof John Wahr of the University of Colorado. "People should be just as worried about the melting of the world's ice as they were before."
His team's study, published in the journal Nature, concludes that between 443-629bn tonnes of meltwater overall are added to the world's oceans each year. This is raising sea level by about 1.5mm a year, the team reports, in addition to the 2mm a year caused by expansion of the warming ocean.
The scientists are careful to point out that lower-altitude glaciers in the Asian mountain ranges – sometimes dubbed the "third pole" – aredefinitely melting. Satellite images and reports confirm this. But over the study period from 2003-10 enough ice was added to the peaks to compensate.
The impact on predictions for future sea level rise is yet to be fully studied but Bamber said: "The projections for sea level rise by 2100 will not change by much, say 5cm or so, so we are talking about a very small modification." Existing estimates range from 30cm to 1m.
Wahr warned that while crucial to a better understanding of ice melting, the eight years of data is a relatively short time period and that variable monsoons mean year-to-year changes in ice mass of hundreds of billions of tonnes. "It is awfully dangerous to take an eight-year record and predict even the next eight years, let alone the next century," he said.
The reason for the radical reappraisal of ice melting in Asia is the different ways in which the current and previous studies were conducted. Until now, estimates of meltwater loss for all the world's 200,000 glaciers were based on extrapolations of data from a few hundred monitored on the ground. Those glaciers at lower altitudes are much easier for scientists to get to and so were more frequently included, but they were also more prone to melting.
The bias was particularly strong in Asia, said Wahr: "There extrapolation is really tough as only a handful of lower-altitude glaciers are monitored and there are thousands there very high up."
The new study used a pair of satellites, called Grace, which measure tiny changes in the Earth's gravitational pull. When ice is lost, the gravitational pull weakens and is detected by the orbiting spacecraft. "They fly at 500km, so they see everything," said Wahr, including the hard-to-reach, high-altitude glaciers.
"I believe this data is the most reliable estimate of global glacier mass balance that has been produced to date," said Bamber. He noted that 1.4 billion people depend on the rivers that flow from the Himalayas and Tibetan plateau: "That is a compelling reason to try to understand what is happening there better."
He added: "The new data does not mean that concerns about climate change are overblown in any way. It means there is a much larger uncertainty in high mountain Asia than we thought. Taken globally all the observations of the Earth's ice – permafrost, Arctic sea ice, snow cover and glaciers – are going in the same direction."
Grace launched in 2002 and continues to monitor the planet, but it has passed its expected mission span and its batteries are beginning to weaken. A replacement mission has been approved by the US and German space agencies and could launch in 2016.
• This article was amended on 9 February 2012. The original sub-heading read "Melting ice from Asia's peaks is much less then previously estimated" as did the photo caption and text: "Melting ice outside the two largest caps - Greenland and Antarctica - is much less then previously estimated". These have all been corrected.
MELTING GLACIERS ON THE HIMALAYAS NOT CONTRIBUTING TOSEA LEVEL RISE
The Himalayas has lost no significant ice over the past decade,
according to a new study, that found melting ice from glaciers is having a much
smaller effect on sea levels than previously thought.
By Louise Gray,
Previous studies relied on
physical measurements of ice caps and glaciers on the ground.
However less than 120 out of more
than 160,000 across the world have actually been measured because of the
difficulty of accessing freezing and remote regions.
The new study,
published in Nature, used satellites to measure the loss of ice from ice caps
and glaciers for the first time from 2003 to 2010.
The results found that overall
ice loss from ice caps and glaciers on land, excluding the huge ice caps on Greenland
and Antarctica , is adding 0.4 mm per year to sea levels compared to
previous projections that estimated 1mm per year.
Mountain glaciers in Asia in
particular are having a much smaller effect than thought, with a “neglible mass
loss” from the Himalayas over the last ten years.
The fact that the satelllite is
measuring ice much higher up the mountain range rather than concentrating on
more accessible glaciers in warmer areas lower down could account for the
change in estimates.
It comes after the “Himalayagate”
scandal that saw the United Nations science body the Intergovernmental Panel on
Climate Change (IPCC) forced to admit it was a mistake to predict the Himalayan
glaciers would melt by 2035.
Jonathan Bamber, of the Bristol
Glaciology Centre at the University of Bristol
He said the new study will help
to understand the effect of climate change on the billions of people living in
areas relying on melt ice and help to understand the long term effect on sea
level rise.
“The contribution of glaciers and
ice caps (excluding the Antarctica and Greenland peripheral GICs) to sea-level
rise was less than half the value of the most recent, comprehensive estimate
obtained from extrapolation of in situ measurements for 2001-05 (0.41 +/- 0.08
compared with 1.1mm yr). Second, losses for the High Mountain Asia region -
comprising the Himalayas , Karakoram, Tianshan, Pamirs and Tibet
The expansion of water as the
oceans warm and the melting of the major ice caps at the Poles are the main
driver of sea level rise, which is predicted to rise by between 30cm and 1m by
2100.
Prof John Wahr, of the University
of Colorado, pointed out that the new way of measuring glaciers using
satellites known as Grace (Gravity Recovery and
Climate Experiment) is
at an early stage and more work needs to be done.
The study shows 148 billion
tonnes of ice, or about 39 cubic miles, was lost annually between 2003 and
2010.
This equates to some 1,000 cubic
miles of ice disappearing between 2003 and 2010 – enough to cover the US
"Our results and those of
everyone else show we are losing a huge amount of water into the oceans every
year," he said. "People should be just as worried about the melting
of the world's ice as they were before."
@ The Telegraph
@ The Telegraph
