By Janet Raloff

Web edition: January 20, 2010

The Intergovernmental Panel on Climate Change acknowledged today that it had erred in projecting the rate and impacts of retreating Himalayan glaciers in a 2007 report. The faulty information appears in one paragraph of a 900-plus page Working Group II report. “In drafting the paragraph in question, the clear and well-established standards of evidence, required by the IPCC procedures, were not applied properly,” the group explained in a prepared statement.

The paragraph in question had claimed that: “Glaciers in the Himalaya are receding faster than in any other part of the world and, if the present rate continues, the likelihood of them disappearing by the year 2035 and perhaps sooner is very high.”

In fact, glaciologist Lonnie Thompson of Ohio State University said this afternoon, Himalayan glaciers are thinning and retreating at a rapid pace, but not at a demonstrably faster rate than in many other parts of the world.

In fact, he said, it’s hard to fully understand how the Himalayas are responding to Earth’s warming because only about 600 of some 46,000 glaciers in that region are being monitored. Of those, 95 percent are in retreat. But it’s hard to understand how much mass the glaciers are losing, Thompson says, without first knowing the depth of affected glaciers — a measure of how much water they hold. And currently, such data are largely nonexistent.

Globally, he says, the glacial census is being rewritten at anything but the proverbial glacial pace. One Andean glacier that has been under study for more than 40 years was retreating at a pace of just 6 meters a year in the early decades. Its retreat has now accelerated to roughly 60 meters a year. Another mountain that used to host six glaciers retains just two remnant ice fields.

Among glaciers within the Brooks Range, which stretches across northern Alaska and Canada’s Yukon, “100 percent” are retreating, he notes. So too, he adds, are 100 percent of glaciers in the tropics (like areas of Peru where Thompson has monitored ice fields for upwards of three decades), roughly 99 percent of the European Alps and more than 95 percent of glaciers in southeastern Alaska.

Overall, glaciers cap some 10 percent of the planet, Thompson observed during a press briefing this afternoon. And the majority of this cold cover appears to be experiencing not only a net loss of aerial extent, but also a drop in the depth of what remains. “Many of these glaciers are now being decapitated,” he explains, since they are losing more snow each year from their tops than is falling down upon them.

For people living downstream of glaciers, the supply of melt water that irrigated fields for millennia could find itself in short supply — lasting only a few decades or centuries. And as melt water finds its way to the sea, ocean levels will inexorably rise. Anyone who doubts the planet is warming need only witness the accelerating loss of ice covering the rooftops of the world, Thompson says.

Current rates of glacial melting do no fall within the natural range of variation that has typically been witnessed in recorded history. Thompson’s data show that some tropical glaciers are uncovering land that has not been icefree in more than 5,000 years.

“Glaciers do not have any political agenda," he says. "They just sum up what is going on in their environment — and react to that.”