The American southwest is in a megadrought. Water levels in lakes are dropping, threatening the local environment as well as agriculture, hydroelectric power, and the people living there. As global temperatures rise, it could be a preview of worse things to come.  Guest: Dr. Jason Smerdon, ocean and climate physicist, and Lamont research professor at the Lamont-Doherty Earth Observatory of Columbia University and co-director at the Earth Institute Faculty.  If you enjoy this show, please consider signing up for Slate Plus. Slate Plus members get benefits like zero ads on any Slate podcast, bonus episodes of shows like Slow Burn and Dear Prudence—and you’ll be supporting the work we do here on What Next. Sign up now at slate.com/whatnextplus to help support our work. Learn more about your ad choices. Visit megaphone.fm/adchoices