As part of our "CBS This Morning" Earth Matters series on Earth Day, co-host Norah O'Donnell spoke with former Secretary of State John Kerry, who was instrumental in the 2016 signing of the international Paris Climate Agreement. He calls President Trump's decision to pull out of the deal stupid and dangerous. Kerry warns of the effects of climate change, including the acceleration of extreme weather events, melting ice and rising sea levels. Plus, he talks about the potential harm to the Democratic party from having such a crowded field of 2020 Democratic presidential hopefuls.