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Old ice gives new clues to climate change

Carbon dioxide levels are much higher than at any time during the past 650,000 years, scientists discover.

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Drilling deep into Antarctic ice, scientists have extended Earth's climate history by another 210,000 years. The new results, they say, drive home two key points:

• Today's atmosphere holds concentrations of carbon dioxide significantly higher than at any time in the last 650,000 years.

• The rise and fall in temperatures track the rise and fall in carbon-dioxide levels as tightly during this additional period as they have over the past 440,000 years.

The results add "another piece of information showing that the time scales on which humans have changed the composition of the atmosphere are extremely short compared to the natural time cycles of the climate system," notes Thomas Stocker, a researcher at the University of Bern in Switzerland and a member of the research team reporting the results.

For ice-core scientist Edward Brook, the results are likely to generate the next icon for long-term climate change. The most telling result, he adds, is the relationship between long-term CO2 trends and long-term temperature trends.

Dr. Brook, with Oregon State University in Corvallis, explains that in these latest results, the warm periods between glacial deep freezes are cooler than those over the past 440,000 years.

Yet the virtual lockstep pattern as temperatures and CO2 levels rise and fall, seen in previous ice cores, holds even for these more-modest swings in global climate.

"It's really striking. The link between temperatures and greenhouse gases is tight," he says.

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