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Atmospheric carbon dioxide highest in 650,000 years
Posted: 04 Dec 2005

Levels of atmospheric carbon dioxide are the highest they have been in 650,000 years, according to the first in-depth analysis of tiny air bubbles trapped in an ice core from East Antarctica.

In two articles analysing air from the ice core published in the journal Science this month, European researchers have extended the greenhouse gas record back to 650,000 years before the present, adding 210,000 years to previous records.

One study chronicles the stable relationship between climate and the carbon cycle during the Pleistocene Era, 390,000 to 650,000 years before the present. The second one documents atmospheric methane and nitrous oxide levels over the same period.

CO2 at record level

The analysis shows that today’s rising atmospheric carbon dioxide concentration, at 380 parts per million by volume, is now 27 per cent higher than its highest recorded level during the last 650,000 years, said Science author Thomas Stocker of the Physics Institute of the University of Bern, Switzerland, who serves as the corresponding author for both papers.

“We have added another piece of information showing that the timescales on which humans have changed the composition of the atmosphere are extremely short compared to the natural time cycles of the climate system,” Stocker said.

This 210,000 year extension of atmospheric carbon dioxide and methane records, encompassing two full glacial cycles, should help scientists better understand climate change and the nature of the current warm period on Earth. The record may also aid researchers in reducing uncertainty in predictions of future climate change and help to clarify when humans began significantly changing the balance of greenhouse gases in Earth’s atmosphere.

A long term research effort known as the European Project for Ice Coring in Antarctica, or EPICA, recovered the new ice core from a site in East Antarctica called EPICA Dome C.

Antarctic site of the ice coring (Photo courtesy Laurent Augustin/European Science Foundation)
Antarctic site of the ice coring that takes research back farther in time than ever before
(Photo courtesy Laurent Augustin/European Science Foundation)

The EPICA Dome C ice core contains hundreds of thousands of years worth of atmospheric air samples within small bubbles trapped in the ice. The air bubbles form when snowflakes fall, and they contain a record of global greenhouse gas concentrations.

'Amazing accomplishment'

The new ice core record described in the two Science papers provides some overlap with a similar record from the Vostok ice core – now, the second longest ice core record - and extends the Vostok record by 210,000 years.

Ed Brook, a professor of geosciences at Oregon State University, who analyzed the studies in the same issue of Science called the research "an amazing accomplishment we would not have thought possible" as recently as 10 years ago."

"Not long ago we thought that previous ice studies which go back about 500,000 years might be the best we could obtain," said Brook, who is also the co-chair of the International Partnerships in Ice Coring Sciences, a group that is helping to plan future ice core research efforts around the world.

"Now we have a glimpse into the past of up to 650,000 years, and we believe it may be possible to go as much as one million years or more," Brook said. "This will give us a fuller picture of Earth's past climates, the way they changed and fluctuated, and the forces that caused the changes. We'll be studying this new data for years."

"The levels of primary greenhouse gases such as methane, carbon dioxide and nitrous oxide are up dramatically since the Industrial Revolution, at a speed and magnitude that the Earth has not seen in hundreds of thousands of years," Brook said. "There is now no question this is due to human influence."

Analysis of the older cores just removed from Antarctica, Brook said, are consistent with some of the quick changes in methane and carbon dioxide levels that are related to abrupt climate change.

It also appears that the natural climate cycles in the distant past – the development and retreat of Ice Ages, for instance – were smaller in magnitude and had less fluctuation in atmospheric gases than what the Earth is now experiencing.

There are critical questions that work of this type may help answer, researchers say such as the relationship between increasing levels of greenhouse gases and global warming.

Ocean currents

There are also concerns that the Earth's climate may have changed very abruptly at times in the past, in complex interactions between the atmosphere, ocean currents and ice sheets.

Past studies of gases trapped in Greenland and Antarctic ice cores have suggested that Earth's temperature can sometimes change amazingly fast, warming as much as 15 degrees in some regions within a couple of decades.

At the same time, there are concerns about the change of major ocean currents, such as those in the North Atlantic Ocean, that are responsible for the comparatively mild climate of much of Europe.

If that "thermohaline circulation pattern" were to abruptly shut down, as has happened at times in the past, it could plunge much of the European continent into a climate more closely resembling that of central Canada.

Brook says continuing research will help to address many of these questions. The 17 nation committee he co-chairs is considering a very deep ice coring project in Antarctica that might provide a record of atmospheric gases 1.2 million years ago, or even further back in time.

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