In the late 1960s to the early 1970s, scientists began to notice that rain was becoming more acidic and that it was affecting the temperate deciduous forests. In places such as power plants, the industrial furnaces were burning a lot of coal which led to sulfur dioxide. The sulfur dioxide would drift in the wind and would combine with water, making a source of acid rain. Another type of acid rain is nitric acid. In extremely hot temperatures, nitrogen within the atmosphere would oxidize, creating nitrogen oxide which mixes with the water in the atmosphere, creating more acid rain. Even though it is said that acid rain is the most harmful to the forests, it is'n't. "Acid percipitation" (Allaby 1, 215) is more harmful because acid mist, and acid snow have a larger impact on the temperate deciduous forests since one covers the entire thing being harmed rather than the surface, like acid rain, and the other is on the harmed organism until it melts. Both are extremely hamrful and destroy the forests (Allaby 1, 214-215).