PerspectiveClimate Change

The Ice Age Carbon Puzzle

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Science  11 May 2012:
Vol. 336, Issue 6082, pp. 682-683
DOI: 10.1126/science.1219710

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Between about 24,000 years ago and today, the large ice sheets covering most of Canada and parts of Europe and Asia melted away, sea level rose by 120 m, Earth warmed by about 5°C, and rainfall and vegetation patterns shifted, sometimes abruptly. This dramatic natural climate experiment was set in motion by cyclic variations in the geometry of Earth's orbit, but a complex system of feedbacks governed the transition from a glacial to an interglacial state. One of the most important of these feedbacks was a well-documented change in the atmospheric greenhouse gas carbon dioxide (CO2) (1). On page 711 of this issue, Schmitt et al. (2) provide important new carbon isotopic data that help to explain these changes.