CO2 Levels Highest in Two Million Years

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Though he'd like to see the study results replicated for good measure, DePaolo is impressed by the report. For dates where the ice-core and plankton data overlap, the CO2 levels match, which suggests the new data for older time periods is accurate too.

Ice Age Theory Debunked?

The study team, led by geochemist Bärbel Hönisch, found evidence disproving the theory that the longer, stronger ice ages that kicked in about 850,000 years ago were caused by a steady, ongoing drop in CO2. Instead, CO2 levels seesawed over the 2.1 million years, dropping during ice ages then bouncing back.

What's more, the average CO2 level during warm periods was 38 percent lower than the average we see today.

That's significant, because it means that scientists will have to look back even further in time to find global warming answers.

Hönisch's next goal is to do just that.

"We know from the geologic record that, around 55 million years ago, the deep-sea temperature suddenly rose by 8 degrees C [14 degrees F]," said Hönisch, of the Lamont-Doherty Earth Observatory in Palisades, New York.

"It's a time that we would like to study, because it's probably the closest thing we'll find to what's happening today. And that's the best way to make estimates for our future."

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