By Richard Black
Environment correspondent, BBC News website
Neither satellites nor ground observations give a complete picture
The vice-chairman of the UN's climate science panel has admitted it made a mistake in asserting that Himalayan glaciers could disappear by 2035.
The Intergovernmental Panel on Climate Change (IPCC) included the date in its 2007 assessment of climate impacts.
A number of scientists have recently disputed the 2035 figure, and Jean-Pascal van Ypersele told BBC News that it was an error and would be reviewed.
But he said it did not change the broad picture of man-made climate change.
The issue, which BBC News first reported on 05 December, has reverberated around climate websites in recent days.
Some commentators maintain that taken together with the contents of e-mails stolen last year from the University of East Anglia's Climatic Research Unit, it undermines the credibility of climate science.
Dr van Ypersele said this was not the case.
"I don't see how one mistake in a 3,000-page report can damage the credibility of the overall report," he said.
"Some people will attempt to use it to damage the credibility of the IPCC; but if we can uncover it, and explain it and change it, it should strengthen the IPCC's credibility, showing that we are ready to learn from our mistakes."
The claim that Himalayan glaciers could disappear by 2035 appears to have originated in a 1999 interview with Indian glaciologist Syed Hasnain, published in New Scientist magazine.
The figure then surfaced in a 2005 report by environmental group WWF - a report that is cited in the IPCC's 2007 assessment, known as AR4.
An alternative genesis lies in the misreading of a 1996 study that gave the date as 2350.
AR 4 asserted: "Glaciers in the Himalayas are receding faster than in any other part of the world... the likelihood of them disappearing by the year 2035 and perhaps sooner is very high."
Dr van Ypersele said the episode meant that the panel's reviewing procedures would have to be tightened.
The row erupted in India late last year in the run-up to the Copenhagen climate summit, with opposing factions in the government giving radically different narratives of what was happening to Himalayan ice.
IPCC chief Rajendra Pachauri has been criticised by Jairam Ramesh
In December, it emerged that four leading glaciologists had prepared a letter for publication in the journal Science arguing that a complete melt by 2035 was physically impossible.
"You just can't accomplish it," Jeffrey Kargel from the University of Arizona told BBC News at the time.
"If you think about the thicknesses of the ice - 200-300m thicknesses, in some cases up to 400m thick - and if you're losing ice at the rate of a metre a year, or let's say double it to two metres a year, you're not going to get rid of 200m of ice in a quarter of a century."
The row continues in India, with Environment Minister Jairam Ramesh calling this week for the IPCC to explain "how it reached the 2035 figure, which created such a scare".
Meanwhile, in an interview with the news agency AFP, Georg Kaser from the University of Innsbruck in Austria - who led a different portion of the AR4 process - said he had warned that the 2035 figure was wrong in 2006, before AR4's publication.
"It is so wrong that it is not even worth discussing," he told AFP in an interview.
He said that people working on the Asia chapter "did not react".
He suggested that some of the IPCC's working practices should be revised by the time work begins on its next landmark report, due in 2013.
But its overall conclusion that global warming is "unequivocal" remains beyond reproach, he said.