National Public Radio: Thursday night, a committee in the House of Representatives passed an ambitious climate bill — a big step toward having a law that controls greenhouse gases. At the heart of the bill is a mechanism called cap-and-trade. It’s a careful mix of government mandate and free-market economy. How successful it will be is a matter of some debate. Cap-and-trade is one of those wonky terms that have permeated the world of Washington, D.C. Part of its mystique is that a lot of people don’t know …