Underexposed

Correction at 3:30 p.m. PST Thursday: Blame my Rust Belt ignorance. The Ohio river that burned is the Cuyahoga.

The retreat of the Jakobshavn Glacier on western Greenland is accelerating, Thompson said. Shown here are lines indicating the location of the end of the glacier starting in 1850 at the far left. The furthest yellow line on the right is 2000, and the two red lines are 2003 and, at far right, 2005.

(Credit: Lonnie Thompson/Ohio State University)

SAN FRANCISCO--I've been spending some time at the the American Geophysical Union conference here, and I've had a recurring thought: When it comes to apocalyptic predictions, geophysicists have the Book of Revelations beat, hands down.

Sometime in the last few years, the idea that global warming is a reality and that it's caused in large measure by people has finally started sinking in. But perhaps because of the remaining skepticism, and more likely because of the fascinating research involved, scientists just can't leave the issue alone.

Global warming has been a major theme among the 14,500 scientists who have converged here for the 40th AGU conference. Seemingly, they can't get enough of it: A year after former Vice President Al Gore addressed conference attendees during the height of hype around his Inconvenient Truth documentary, organizers again gave the stage to an articulate speaker on the issue. This time it was Lonnie Thompson, an Ohio State University scientist who has spent innumerable hours drilling into icecaps at the world's highest elevations.

Lonnie Thompson at AGU

(Credit: Stephen Shankland/CNET News.com)

Global warming, a decades-old idea that posits certain greenhouse gases will keep heat from escaping into space, has moved gradually from a prediction to a measurable phenomenon. But for those who are inclined to feel comfort that scientists got it right, Thompson had sobering words on Wednesday evening: the pace of glacial melting is accelerating, and scientists don't have a handle on the new patterns.

"We're in unfamiliar territory," Thompson said. "The observed rapid changes in Greenland and Antarctica are not predicted. What we're seeing is fast glacier flow."

Thompson uses yaks to carry back each one of hundreds of six-foot ice core samples retrieved from holes drilled in glaciers.

(Credit: Lonnie Thompson/Ohio State University)

Take the Jacobshavn Ice Stream, a glacier on the west side of Greenland that drains about 6.5 percent of the continent's massive ice sheet. Between 2000 and 2003, its rate of retreat nearly doubled. Scientists expected a slow and linear response to global warming, but instead the response has been fast and accelerating. Another example is the Qori Kalis Glacier in Peru, whose initial retreat rate around 1991 was about 6 meters per year but now is 60 meters per year.

"It's not just retreating. It's an exponential increase," he said.

Humanity has a lousy track record dealing with environmental crises before they become severe, he said, pointing as an example to Ohio's famously polluted Cuyahoga River.

"When did we do anything about that river? When it caught on fire," he said. "We've cleaned it up. Now there are walleye and pike in it. It wasn't that we couldn't do it; it was that we didn't have the political will to do it."

Compared to some crises, though, global warming poses long-term challenges because greenhouse gases stay in the atmosphere 70 to 120 years after being emitted, he said.

This year, melting split the Furtwangler Glacier on Africa's Mt. Kilamanjaro into two halves.

(Credit: Lonnie Thompson/Ohio State University)

Glaciers are only one reflection of overall climate trends, but Thompson believes they're an important one--especially the ones he's specialized in studying, those growing at the tops of high mountains in central latitudes rather than the vast expanses in the Arctic and Antarctic regions.

"Glaciers, especially tropical glaciers, are the canaries in the coal mine for our global climate system," he said.

In his research, Thompson has spent 840 days above 18,000 feet, setting up camps and drilling out cores of ice from the glaciers. The ice cores record in tiny air bubbles volcanic activity and greenhouse gas levels; each year has its own layer that can be dated by characteristic patterns of dust deposition and by wet and dry seasons.

The ice core records are disappearing along with the glaciers, though. Several he's examined, for example, show evidence of above-ground thermonuclear bomb tests from the Soviet Union in the 1960s and the United States in the 1950s. But there's no evidence of either on the Naimona'nyi Glacier on the Tibetan Plateau.

"These glaciers are wasting from the surface down," Thompson said.