Is man-made climate change our biggest problem? Are the wildfires, droughts and hurricanes we see on the news an omen of even worse things to come? The United Nations and many political leaders think so and want to spend trillions of tax dollars to reverse the warming trend. Are they right? Will the enormous cost justify the gain? Economist Bjorn Lomborg, director of the Copenhagen Consensus Center, explains the key issues and reaches some sobering conclusions.