Ancient ice shows warming ahead of CO2

SAN DIEGO, March 13 (UPI) -- A new study released Thursday on how ancient glaciers melted shows increases in atmospheric carbon dioxide actually tended to lag behind warming temperatures by 700 to 900 years.

The findings, coupled with other new data showing an increase in cloudiness in the Arctic from 1982-1999, are adding further insights for computer climate modelers, researchers said.

"The warming during a transition from glacial to interglacial period is due (more) to solar forcing (increased temperatures caused by more sunlight) than to CO2 forcing (increased atmospheric CO2)," Nicolas Caillon, a climatologist at Scripps Institute of Oceanography in San Diego, told United Press International.

Caillon, who is lead author of the study, which appears in the March 14 issue of the journal Science, said the findings are based on analyses of an isotope of the inert gas argon, along with CO2 trapped in air bubbles in a 240,000-year-old core drilled in an Antarctic glacier. Caillon said the analytical method has not been used before.

The findings suggest CO2 increases followed -- rather than preceded -- increases in Earth's temperature some 2,400 centuries ago.

Instead of CO2 buildup, the ancient warming was driven by the Earth's position relative to the sun and the angle of its axis, explained co-researcher Jean Jouzel, a climatologist at the Pierre Simon Laplace Scientific Laboratory near Paris.

"You have changes in the oceanic circulation, which expels CO2, which is deep in the ocean," Jouzel continued. Although the exact mechanism expelling the CO2 is not certain, what is clear -- said both Caillon and Jouzel -- is the role of CO2 in causing the melting of glaciers in the Northern Hemisphere. There, they said, CO2 "may serve as an amplifier" of warming caused by the sun.

"When you start to warm the ocean you have more water vapor in the atmosphere, for example, and this causes positive feedback," producing warming temperatures, Jouzel told UPI.

"By studying the details of the timing of events, we should better understand how the natural climate system works, and thus better understand what the future might hold," said Penn State University geoscientist Richard Alley, who was not involved in the research.

"We still don't know what ... controlled the carbon dioxide changes over ice-age cycles," Alley told UPI. "We do know that the natural changes were much smaller and slower than what humans are now in the process of doing."

Meanwhile, a study of Arctic cloud patterns, also appearing in the March 14 issue of Science, suggests an increase in cloudiness in the polar regions has tended to counteract the effect of global warming.

Using data from dozens of meteorological stations, researchers found although surface and water temperatures have been increasing across the Arctic, because of a not-yet-understood process, Arctic clouds seem to be producing a cooling effect.

The researchers, at the University of Wisconsin in Madison and the National Oceanographic and Atmospheric Administration report satellite data show cloudiness increased across the Arctic between 1982 and 1999 during the spring and summer, accompanied with higher temperatures. Then the polar region cooled and became less cloudy during the winter.

Although many researchers have monitored Arctic temperatures and sea ice extent, few have studied other climate-related factors in the region, including how all the factors interact.

"To understand how and why the climate is changing, you have to think about the feedback systems," said Xuanji Wang, the study's lead author.

Clouds play an important role in such systems, Wang explained. Not only do they reflect the sun's energy, but they also can trap heat emitted by the Earth, thereby contributing to warming.

Team member Jeffrey Key, an atmospheric scientist working both at NOAA and at UW-Madison's Cooperative Institute for Meteorological Satellite Studies, told UPI he is not sure why there has been an increase in atmospheric moisture in the Arctic and a corresponding increase in clouds, but the phenomenon demonstrates how the Arctic is linked with rest of the planet.

"We're speculating that the increase in moisture is coming from outside the Arctic so the change is related to large-scale circulation, rather than local processes," Key said.

He said a weather pattern, known as the Arctic Oscillation -- which links Arctic weather to meteorologic patterns as far south as the Mediterranean -- likely is responsible for the cloud changes. But the details are not yet clear, he added.

For example, although spring and summer cloud cover over the Arctic has increased by 2 percent to 4 percent per decade, the researchers said, winter cloud coverage has decreased. The average result was no change.

Therefore, Key said, "the average annual change doesn't tell the whole story (about Arctic warming)." On the other hand, he explained, "the Arctic is a place where small changes can have big effects. These effects can signal climate changes elsewhere. That's why it's so important to monitor the Arctic."

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(Reported by Harvey Black, UPI Science News, in Madison, Wis.)