New data, taken from the lowest 200 meters of the so-called EPICA Dome C Antarctic ice core, extend the historical records for atmospheric carbon dioxide and methane concentrations by 150,000 years — or two complete glacial cycles. The data also yield a complete reconstruction of the history of these two greenhouse gases over the past 800,000 years.
Members of the EPICA (European Project for Ice Coring in Antarctica) collaboration obtained the new data by measuring the composition of air trapped in the ice core. They report their findings and analyses in two papers published in Nature this week.
According to a related ‘News & Views’ article by Ed Brook of Oregon State University, “The fundamental conclusion that today’s concentrations of these greenhouse gases have no past analogue in the ice-core record remains firm.” Brook also notes that: “The remarkably strong correlations of methane and carbon dioxide with temperature reconstructions also stand.”
Thomas Stocker and colleagues report that analysis of the composition of air bubbles trapped in this core, which was drilled to just meters above bedrock, reveals the lowest concentration of carbon dioxide measured in an ice core to date. They also report that atmospheric carbon dioxide is strongly correlated with Antarctic temperature throughout the past eight glacial cycles, but with significantly lower concentrations between 650,000 and 750,000 years before present. The researchers suggest that interactions between climate and methane emissions from wetlands in the tropical and boreal (high-northern-latitude) regions probably controlled the atmospheric methane budget.
Ice-core scientists are now aiming to establish a continuous 1.5 million-year record, according to Brook.
- Windows on the greenhouse (News & Views p291, doi: 10.1038/453291a)
- High-resolution carbon dioxide concentration record 650,000-800,000 years before present (Letter p379, doi: 10.1038/nature06949)
- Orbital and millennial-scale features of atmospheric CH4 over the past 800,000 years (Letter p383, doi: 10.1038/nature06950)
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