Abrahm Lustgarten, a Pulitzer Prize-nominated environmental reporter, talks to us about climate migration, one of climate change's biggest looming threats. Rising temperatures, rising sea levels, and ever-increasing natural disasters are forcing people to abandon their homes and their ways of life to seek safer ground. As the planet heats up, the number of climate refugees will just keep swelling, up to 3 billion people -- a third of the global population -- by 2070.