In the atmosphere sulphur oxides (see sulphur dioxide) are converted to sulfuric acid. Oxides of sulphur and nitrogen combine with atmospheric moisture to produce acid rain. Although some sulphur oxides are introduced into the atmosphere by natural means, such as volcanic eruptions, the majority of the sulphur oxides responsible for the damaging effects of acid rain come from anthropogenic sources, mainly the burning of fossil fuels. Areas in the northeastern United States , eastern Canada , and northern Europe have suffered damage due to the effects of acid rain. In many areas damage to forests, crops, lakes, and streams are so severe that they are completely devoid of any life forms. Steps are now being taken in many parts of the world to reduce the amount of sulphur dioxide introduced into the atmosphere. In 1990, amendments where made to the Clean Air Act that places restrictions on the release of sulphur dioxides by power plants. The amendment calls for the reduction of sulphur emissions from a 1990 level of nearly 20 million tonnes per year to approximately 10 million tonnes per year by January 1, 2000.