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November 25, 2005

Rise in Gases Unmatched by a History in Ancient Ice

By ANDREW C. REVKIN
http://www.nytimes.com/2005/11/25/science/earth/25core.html

Shafts of ancient ice pulled from Antarctica\'s frozen depths show that for
at least 650,000 years three important heat-trapping greenhouse gases
never reached recent atmospheric levels caused by human activities,
scientists are reporting today.

The measured gases were carbon dioxide, methane and nitrous oxide.
Concentrations have risen over the last several centuries at a pace far
beyond that seen before humans began intensively clearing forests and
burning coal, oil and other fossil fuels.

The sampling and analysis were done by the European Program for Ice Coring
in Antarctica, and the results are being published today in the journal
Science.

The evidence was found in air bubbles trapped in successively older ice
samples extracted from a nearly two-mile-deep hole drilled in a remote
spot in East Antarctica called Dome C.

Experts familiar with the findings who were not involved with the research
said the samples provided a vital long-term view of variations in the
atmosphere and Antarctic climate. They say the data will help test and
improve computer models used to forecast how accumulating greenhouse
emissions will affect the climate.

Some climate experts not involved in the research said the findings also
confirmed that the buildup of carbon dioxide and other heat-trapping
smokestack and tailpipe emissions was taking the atmosphere into uncharted
territory.

The longest previous record of carbon dioxide fluctuations, compiled from
ice cores collected at the Russian research station at Vostok, in East
Antarctica, goes back slightly more than 400,000 years.

\"They\'ve now pushed back two-thirds of a million years and found that
nature did not get as far as humans have,\" said Richard B. Alley, a
geosciences professor at Pennsylvania State University who is an expert on
ice cores. \"We\'re changing the world really hugely - way past where it\'s
been for a long time.\"

James White, a geology professor at the University of Colorado, Boulder,
not involved with the study, said that although the ice-age evidence
showed that levels of carbon dioxide and the other greenhouse gases rose
and fell in response to warming and cooling, the gases could clearly take
the lead as well.

\"CO2 and climate are like two people handcuffed to each other,\" he said.
\"Where one goes, the other must follow. Leadership may change, or they may
march in step, but they are never far from each other. Our current CO2
levels appear to be far out of balance with climate when viewed through
these results, reinforcing the idea that we have significant modern
warming to go.\"

The new data from the ice cores also provides the first detailed portrait
of conditions during ice-age cycles that occurred more than 400,000 years
ago - a point in Earth\'s two-million-year history of cold periods and warm
intervals after which some unknown influence lengthened ice ages and
shortened and amplified the warm periods.

Both before and after that transition, the ice record shows, there was
always a tight relationship between amounts of the greenhouse gases and
air temperature.

While the overall climate pattern has been set by rhythmic variations in
Earth\'s orientation to the Sun, the records show that carbon dioxide and
methane consistently made the interglacial climate warmer than it would
otherwise have been, said Thomas Stocker, one of the researchers and a
physicist at the University of Bern in Switzerland.

Last year, the same cores provided new evidence that the current warm
period, the Holocene, which began about 12,000 years ago, is similar to
the longer warm periods that were typical before 400,000 years ago, and
could last at least another 16,000 years.

The European team is analyzing deeper, older sections of the Dome C ice
cores, and the researchers said they might be able to take the climate
record back 800,000 years, possibly providing information about yet
another early warm interval similar to the Holocene.

The new long-term record is essentially creating a subset of climate
science, letting scientists compare different warm periods. They can then
sort out influences, including greenhouse gases, said Gavin A. Schmidt, a
climate modeler at the Goddard Institute for Space Studies in Manhattan.

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