CORVALLIS - The study of gases trapped in ancient glacial ice cores from Greenland and Antarctica is confirming that the Earth's temperature and atmospheric makeup can sometimes change amazingly fast, warming as much as 15 degrees in some regions within a couple of decades.

Changes of this speed and magnitude are probably due to an abrupt shift in an important climatic mechanism such as ocean circulation patterns or other forces, which affect the entire world but are not yet fully understood, say researchers at Oregon State University who study this phenomenon.

But the growing body of evidence from work in this field also indicates that what goes up in one hemisphere may simultaneously go down in the other - a "see-saw" effect in which the Northern Hemisphere may begin to cool rapidly just as the Southern Hemisphere and Antarctica are warming up.

"These are very complex climate mechanisms at work, but our study of gases trapped in glacial ice is giving us a very clear indication of what has happened in the past and how long it took," said Edward Brook, an associate professor and paleoclimatologist in the OSU Department of Geosciences. "It's not as certain exactly what is causing the changes, although our research is supportive of the theory that shifts in circulation patterns of the North Atlantic Ocean could be involved."

One key to this riddle, Brook said, is the study of methane - a "greenhouse" gas that can itself cause global warming, but also a gas that is found at higher levels in a global climate that has been warmed from some other cause. When the climate warms from any cause, things such as expanding wetlands should produce larger amounts of methane.

"Our studies have shown that every time you get a major shift in climate, you also get a large jump in methane levels shortly afterward," Brook said.

"The impact on atmospheric gases is global and can easily be seen in both the Northern and Southern Hemisphere. But it appears that the temperature changes themselves may oscillate, with the Northern Hemisphere cooling down at the same time it warms in Antarctica."

These shorter term shifts in climate can go up and down within larger trends such as ice ages or the "interglacial" warm periods such as the one the Earth is now experiencing. But the implications could be of profound importance, Brook said.

"What's becoming increasingly clear is that the Earth has experienced abrupt climatic change, on the order of years or decades," he said. "This has become a major area of research, because we need to know how these global systems can go through such big jumps in such short periods of time."

One theory that has been outlined, by OSU researchers and others, is the shutdown or startup of what's called a "thermohaline circulation" pattern in the North Atlantic. Based on changes in salinity, terrestrial precipitation, water temperature and other factors, this huge current system is part of what keeps most of Europe warm when it is functioning. But it also appears the current can be shut down rather abruptly, with global climate implications - not the least of which is plunging Europe into a giant deep freeze.

Other researchers, Brook said, believe tropical ocean and atmospheric forces are the underlying causes of climate changes of this speed and magnitude. And some have pointed to release of methane hydrate deposits on the seafloor as playing a possible role. The scientific debate on the cause of the climate changes is continuing, he said.

The methane itself, Brook said, appears to be more of an indicator of climate change than an immediate cause of it. Methane levels in the atmosphere are now at about 1,800 parts per billion - more than double any level ever found prior to the Industrial Revolution.

According to Brook, the gases found in ice cores are remarkably well preserved and give a very accurate representation of atmospheric content at snapshots in time. And they are old. Some are at least 440,000 years old, and some cores just drilled in Antarctica may be as much as 1 million years old, he said.

Studies such as this are also expanding due to the critical importance of the issues involved, Brook said. The OSU research, done in collaboration with the Scripps Institute at the University of California - San Diego, recently attracted a new $330,000 grant from the Gary Comer Foundation to support the development of improved measuring techniques. Most past funding has come from the Division of Polar Programs of the National Science Foundation.

New drilling activities in Antarctica may be planned in coming years, Brook said, to produce extremely deep cores and better identify the underlying causes of these rapid changes in Earth's past climate.