What factors influence the input and output of carbon through earth's spheres? the oceans on earth act as carbon sinks. the combustion of fossil fuels contributions to an increase in atmospheric carbon dioxide. animals are solely responsible for the release of carbon dioxide via respiration. atmospheric co2 is continuously exchanged with the oceans and on land. man's activities on earth contribute to the decrease of atmospheric co2. vegetation and soil take in more co2 than they release.