Clues to global warming from tiny bubbles

WASHINGTON -- There is more carbon dioxide in the atmosphere today than at any point during the last 650,000 years, says a major new study that let scientists peer back in time at greenhouse gases that can help fuel global warming.

By analyzing tiny air bubbles preserved in Antarctic ice for millennia, a team of European researchers highlights how people are dramatically influencing the buildup of these gases.

The remarkable research promises to spur "dramatically improved understanding" of climate change, said geosciences specialist Edward Brook of Oregon State University.

The study, by the European Project for Ice Coring in Antarctica, was published today in the journal Science.

Today, scientists directly measure levels of carbon dioxide and other greenhouse gases, which accumulate in the atmosphere as a result of fuel-burning and other processes. Those gases help trap solar heat, like the greenhouses for which they are named, resulting in a gradual warming of the planet.

Those measurements are disturbing: Levels of carbon dioxide have climbed from 280 parts per million two centuries ago to 380 ppm today. Earth's average temperature, meanwhile, increased about 1 degree Fahrenheit in recent decades, a relatively rapid rise. Many climate specialists warn that continued warming could have severe effects, such as rising sea levels and changing rainfall patterns.

Skeptics sometimes dismiss the rise in greenhouse gases as part of a naturally fluctuating cycle. The new study provides ever-more definitive evidence countering that view, however.

Deep Antarctic ice encases tiny air bubbles formed when snowflakes fell over hundreds of thousands of years. Extracting the air allows a direct measurement of the atmosphere at past points in time, to determine the naturally fluctuating range.

A previous ice-core sample had traced greenhouse gases back about 440,000 years. This new sample, from East Antarctica, goes 210,000 years further.

Today's still-rising level of carbon dioxide already is 27 percent higher than its peak during all those millennia, said lead researcher Thomas Stocker of the University of Bern, Switzerland.

Moreover, that rise is occurring at a speed that "is over a factor of a hundred faster than anything we are seeing in the natural cycles," Stocker added. "It puts the present changes in context."

Researchers also compared the gas levels to the Antarctic temperature over that time period, covering eight cycles of alternating glacial or ice ages and warm periods. They found a stable pattern: Lower levels of gases during cold periods and higher levels during warm periods.

The bottom line: "There's no natural condition that we know about in a really long time where the greenhouse gas levels were anywhere near what they are now," said Oregon State's Brook.