Fossil leaves bear witness to ancient carbon dioxide levels

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Science  06 Jan 2017:
Vol. 355, Issue 6320, pp. 14-15
DOI: 10.1126/science.355.6320.14

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There are lessons for climate scientists buried in the past. Carbon dioxide (CO2) levels surged many times millions of years ago, triggering ancient bouts of climate change. But the evidence is hazy: Models of ancient atmospheres and tools for teasing out past CO2 levels from fossils and rocks all have limitations. Now, scientists have developed a new method for wringing CO2 estimates from fossilized leaves—one that can go deeper into the past, and with more certainty. And it is delivering some unsettling news: It suggests that for the same amount of injected CO2, temperatures might rise further than current models predict.