WWF's Keya Chatterjee discusses protecting the planet by installing solar panels on her home in Washington, DC.
When the Earth Systems Research Laboratory announced that atmospheric carbon dioxide concentrations reached more than 400 ppm, it made the news.
But why is it that the 400 ppm mark gets our attention? Why wasn't it newsworthy when we hit record levels of 399 ppm? Or 398 ppm?
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