In order to reduce emissions of planet-warming greenhouse gases, President Obama has suggested that by 2035, the U.S. should get 80 percent of its electricity from clean energy sources.

Today, nearly half of our electricity comes from coal, but this is a dirty source of energy. In order to reach the 80% goal, we would need to replace nearly two thirds of our coal power with energy sources like hydropower, wind, solar, nuclear, and natural gas—or with coal- burning plants where carbon emissions are captured and kept out of the atmosphere. These all emit some greenhouse gases, but far less than coal plants.