PNAS Cover image: Pictured is a fragment of Antarctic glacial ice with embedded air bubbles. Thomas K. Bauska et al. measured the isotopic composition of carbon dioxide trapped in the ice to study changes in Earth's atmosphere during the last deglaciation between 20,000 and 10,000 years ago. The results reveal several instances of rapid rise in atmospheric carbon dioxide and suggest that two events were driven by a loss of land carbon that occurred over hundreds of years. See the article by Bauska et al. on pages 3465–3470. Image courtesy of Thomas K. Bauska.
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