CO2 levels reach 2.1-million-year peak
Carbon dioxide levels in the Earth’s atmosphere have reached the highest levels for 2.1 million years, according to the results of a detailed investigation into the climate record locked in the shells of tiny marine fossils extracted from the ocean floor.
Bärbel Hönisch, a geochemist at Lamont-Doherty Earth Observatory, New York, and her colleagues reconstructed CO2 levels over the past
2.1 million years by analysing the ratio of boron isotopes in the shells of single-celled plankton called foraminifera collected from sediments under the Atlantic Ocean, off the coast of Africa. From these data, they were able to tell how much CO2 was in the air at the time the organisms lived.
They discovered that over the past 2.1 million years, CO2 levels never exceeded 300 parts per million; current atmospheric CO2 levels have reached 385 parts per million.
The study also disproved the theory that a period of more intense and prolonged ice ages that began 850,000 years ago was triggered by falling levels of CO2 in the atmosphere, as proposed by some climate scientists.
August 2009
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