The US government estimates that every ton of carbon dioxide emitted into the atmosphere generates at least $40 in damages by contributing to climate change, but the Swedish government says the figure is closer to 100 euros, and it charges a tax to reflect that. Our guest, Gernot Wagner, says both figures are way too low. Today, he explains how economists blend climate science with financial accounting to come up with a price on carbon.

Plus: What's more effective -- cap-and-trade, or a carbon tax? We offer a primer on that debate.