Atmospheric CO2 Has Reached Levels Not Seen in 14 Million Years, New Study Finds

The last time that levels of atmospheric carbon dioxide were as high as they are today, Greenland was free of ice and the savanna and grassland ecosystems where humans evolved didn’t exist yet. That’s the conclusion of a study published in Science Friday, which researchers say compiles “the most reliable data available to date” on atmospheric carbon dioxide levels over the last 66 million years.

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