Fiona Harvey Himalayan glaciers – another Climategate? Not quite.

The Himalayan glaciers are melting – on that climate change scientists agree. But how fast?

That question should have been an interesting academic footnote, but now it is the subject of a fresh controversy that climate change scientists could well have done without.

The Intergovernmental Panel on Climate Change’s 2007 Fourth Assessment Report contained an estimate that most of the Himalaya’s glaciers could disappear by 2035.

But the authors are now being accused of sloppy methods, after the New Scientist uncovered that it was the source of that claim.

Last week, the New Scientist traced the claim back to an article it ran in 1999, reporting the view of the leading Indian glaciologist Syed Hasnain, that all the glaciers in the central and eastern Himalayas could disappear by 2035.

This claim was not repeated by Mr Hasnain in peer-reviewed literature, but was picked up in a report by WWF, the environmental campaigning group, which was the source for the inclusion of the claim by the IPCC.

The claim is pretty strong stuff, as the disappearance of the glaciers would condemn hundreds of millions of people to water shortages.

Other glacier experts have said that while the Himalaya’s glaciers are certainly melting, at current rates of warming, it would take much longer than 25 years for them to disappear altogether – ten times as long, perhaps.

The IPCC has agreed to re-examine the estimate.

But the embarrassment is one that climate scientists certainly didn’t need.

Scientists have moved to discount the importance of the claim, dismissing it as merely a minor detail in a report that was thousands of pages long and drew on data from many thousands of sources. Moreover, says Bob Ward of the Grantham Institute on the Guardian’s web site, the Himalayan claim was not included in the key document arising from the report, the summary for policymakers, which was presented to governments to help them draft a response to the problem of global warming. The claim was also not used by the IPCC in any other major fora, and was not relied on by the IPCC to draw the key conclusions in its 2007 report.

But coming so soon after the Climate gate emails, which appeared to show scientists planning to withhold data and manipulate the presentation of certain data, the fresh controversy over the IPCC’s methods is another battering for climate scientists.

This is not as bad as the Climate gate emails, relating as it does to a relatively minor claim. It will encourage the Indian government, which recently commissioned a report to show that the Himalayan glaciers are not melting as fast as some feared.

But it is another fillip for the sceptics. Episodes like this are damaging to the credibility of climate scientists, and are frustrating for the vast majority of those who are careful, accurate and conscientious in their methods.