The date appeared in the IPCC's Fourth Assessment Report (4AR), which read: "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."
A number of scientists had recently disputed the date, after a row erupted in India late last year in the run-up to the Copenhagen climate summit, which BBC News reported on 05 December.
Opposing factions in the Indian government gave radically different opinions of what was happening to Himalayan ice.
Dr Pachauri said the inclusion of the 2035 date in the 4AR, which was published in 2007, was "a case of human error", adding that it was unfortunate that it had happened.
"However, let me emphasise that this does not in any way detract from the fact that the glaciers are melting, and this is a problem that we need to be deeply concerned about."
He told BBC News that he became aware of the error "maybe around the 16th or 17th of January".
"Then we swung into action," he explained.
"I got the entire top team of the IPCC to go through the details of this case, and we decided that this was an error but we also saw that this did not in any way move away from the reality that these glaciers are melting."
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 was cited in AR4.
An alternative genesis lies in the misreading of a 1996 study by a Russian researcher that gave the date as 2350.
In a separate development, a report in the UK's Sunday Times newspaper said the IPCC faced "new controversy for wrongly linking global warming to an increase in the number and severity of natural disasters", in its 2007 milestone report.
However, the IPCC issued a statement that said the story was "misleading and baseless".
It stated: "The assessment addresses both observations of past changes and projections of future changes in sectors ranging from heat waves and precipitation to wildfire.
"Each of these is a careful assessment of the available evidence, with a thorough consideration of the confidence with which each conclusion can be drawn.
"In writing, reviewing, and editing this section, IPCC procedures were carefully followed to produce the policy-relevant assessment that is the IPCC mandate."
Some commentators maintain that these developments, 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.
"It is about the process with which it comes to its conclusions; how they pick and choose papers, how they emphasise certain problems and how they exaggerate certain potential risks - that is at issue here," Dr Benny Peiser, for the UK-based Global Warming Foundation, told BBC News.
But a defiant Dr Pachauri said: "I want to tell the sceptics... who see me as the face and the voice of the science of climate change, I am in no mood to oblige them; I am going to remain as chairman of the IPCC for my entire term."
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