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Research has shown that although some of the damage attributed to acid rain is a result of natural causes, sulphur dioxide from oil and coal combustion and nitrogen oxides produced from automobile engines have greatly Intensified the acid- rain problem. Winds can carry the pollutants thousands of kilometres away from their source. The British government has recognized that sulphur emissions from power plants in the United Kingdom are contributing to acid deposition in Scandinavia. Canadian emissions contribute substantially to acid rain in the north-eastern United States, for example, and much of the sulphur falling in eastern Canada is believed to originate in the United States. In l986 the U.S. National Academy of Sciences acknowledged That acid rain from U.S. sources had become a serious problem in' the eastern United States and Canada. The Canadian government agreed to reduce sulphur dioxide emissions, yet the United States did not place limitations on its sulphur emissions that might drift into Canada. Nowadays, scientists agree that acid rain is harmful, but reports concerning its severity conflict.