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400 PPM: Carbon Dioxide in the Atmosphere Reaches Prehistoric Levels

400 PPM: What’s Next for a Warming Planet Concentrations of greenhouse gases in the atmosphere have reached this level for the first time in millions of years. What does this portend? » On May 2, after nightfall shut down photosynthesis for the day in Hawaii, carbon dioxide levels in the atmosphere touched 400 parts-per-million there [...]

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