This chapter looks at what happens when we burn coal, oil, or natural gas in power plants to make energy. A major point is why coal produces so much more of the greenhouse gas carbon dioxide than oil does, which in turn is worse than natural gas per unit of energy produced. Detailed examples are given about using different fuels to generate electricity and how what happens when you leave your computer or lights on all of the time depends on what fuel produces the electricity. We hear constantly that carbon dioxide is a greenhouse gas, but why? The reason that carbon dioxide is such an important greenhouse gas is shown to be caused by the fundamental quantum mechanical phenomena of black body radiation and quantized energy levels. These phenomena were discussed earlier in the book. Here it is shown how they come together to make carbon dioxide such a dangerous greenhouse gas.