humans are responsible for 1/3 of the sulfur in the atmosphere. sulfur is released by the combustion of fossil fuels, as mentioned above, and is most prevalent as sulfur dioxide. sulfur is one of the root causes of acid rain along with nitrogen and carbon which negatively affects the environment. acid rain is created when the h2o falls and combines with the sulfur trioxide to create sulfuric acid. sulfuric acid is also used in most fertilizers and so can be introduced into the water cycle from runoff off of nearby farms into rivers and lakes. this causes eutrophication and algal blooms, and so reduced the dissolved oxygen and biodiversity in that water system. sulfur in the atmosphere as sulfur dioxide also absorbs radiation, however which keeps the earth's surface cooler and combats some of the effects of global warming.