U.N. Panel’s Glacier Warning Is Criticized as Exaggerated

A much-publicized estimate from a United Nations panel about the rapid melting of Himalayan glaciers from climate change is coming under fire as a gross exaggeration.

The United Nations Intergovernmental Panel on Climate Change said in 2007 — the same year it shared the Nobel Peace Prize with former Vice President Al Gore — that it was “very likely” that Himalayan glaciers would disappear by 2035 if current warming trends continued.

That date has been much quoted and a cause for enormous consternation, since hundreds of millions of people in Asia rely on ice and snow melt from these glaciers for their water supply.

The panel, the United Nations’ scientific advisory body on climate change, ranks its conclusions using a probability scale in which “very likely” means there is greater than 90 percent chance that an event will occur.

But it now appears that the estimate about Himalayan glacial melt was based on a decade-old interview of one climate scientist in a science magazine, The New Scientist, and that hard scientific evidence to support that figure is lacking. The scientist, Dr. Syed Hasnain, a glacier specialist with the government of the Indian state of Sikkim and currently a fellow at the TERI research institute in Delhi, said in an e-mail message that he was “misquoted” about the 2035 estimate in The New Scientist article. He has more recently said that his research suggests that only small glaciers could disappear entirely.

The panel, which relies on contributions from hundreds of scientists, is considering whether to amend the estimate or remove it.

“The I.P.C.C. considers this a very serious issue and we’re working very hard to set the record straight as soon as we can,” said Christopher Field, co-chairman of the panel’s section that was responsible for the report, which deals with impacts, adaptation and vulnerability.

He noted that the potentially erroneous figure in question had appeared only in the panel’s full report of more than 1,000 pages and had been omitted in later summary documents that the panel produced to guide policy. The summaries said only that the Himalayan glaciers “could decay at very rapid rates” if warming continued. Such documents are produced after panel members review a full-length report, although if a figure in the report is deemed to be in error, it is supposed to be removed.

Still, the revelation is the latest in a string of events that climate change skeptics have seized on to support their contention that fears about warming are unfounded, or at least overblown. Late last year, hackers obtained private e-mail messages from leading researchers at the University of East Anglia in England suggesting they were altering the presentation of some data in a way that emphasized the human influence on climate change.

The flawed estimate raises more questions about the panel’s vetting procedures than it does about the melting of Himalayan glaciers, which most scientists believe is a major problem. But the panel’s reports are the basis for global policy and their conclusions are widely heeded.

“The Himalayan glaciers will not disappear by 2035 — that is an overstatement,” said Dr. Bodo Bookhagen, an assistant professor at the University of California at Santa Barbara who studies the effect of climate change at high altitudes. “That number somehow got incorporated into the I.P.C.C. report, and that probably shouldn’t have happened.”

Still, he added: “It is very clear that there is glacier retreat and that it has devastating impact.”

There is mounting proof that accelerating glacial melt is occurring, although the specifics are poorly defined, in part because these glaciers are remote and poorly studied.

At an international conference last year on Asia’s glaciers, held at the University of California, San Diego, Yao Tandong, a Chinese glaciologist who specializes in the Tibetan Plateau, said, “Studies indicate that by 2030 another 30 percent will disappear; by 2050, 40 percent; and by the end of the century 70 percent.” He added: “Actually we don’t know much about process and impacts of the disappearance. That’s why we need an international effort.”