Climate change is the most pressing issue in the world, and the twenty-three Democratic candidates for President have ideas about how to address it. For decades, economists have argued for a cap-and-trade system or a carbon tax as the cheapest and most efficient way to reduce CO2 emissions. Now progressives and climate activists are advocating a different approach, focusing on renewable energy and creating jobs. Their efforts have resulted in the Green New Deal resolutions before Congress. What do the various proposals entail--and would any of them work?