This week’s Please Explain, the third in our series How to Save the World, is about climate change and how to stop it. David Archer, professor of geophysical sciences at the University of Chicago, and author of The Long Thaw: How Humans are Changing the Next 100,000 Years of the Earth’s Climate, and Global Warming: Understanding the Forecast; and Klaus Lackner, Director of the Lenfest Center for Sustainable Energy at Columbia University’s Earth Institute join us to talk about carbon in the atmosphere, how and why it is causing climate change, and how to slow or stop climate change by using sustainable energy and carbon sequestration.