The mining of non-renewable energy and the by-products they leave behind causes damage to the environment. There is little doubt that fossil fuels contribute to global warming. When fossil fuels are burned, nitrous oxides causes photochemical pollution, sulphur dioxide creates acid rain, and greenhouse gases are emitted. A major disadvantage of non-renewable energy is the challenge of breaking humans of their habit of leaning on it. The Union of Concerned Scientists reports it's an uphill battle to sway consumers that the so-called "public goods" of renewable energy, such as reducing pollution for everyone, may not be enough to convince them to pay more for cleaner energy.