Sulfates that form in the atmosphere after volcanic eruptions and rain down on wetlands may decrease those areas' emissions of methane for several years, thereby cooling the global climate. The effect, now documented in a field study, could extend volcanic sulfates' well-known short-term cooling effect.
Large volcanic eruptions send much sulfur dioxide high into the atmosphere, where the gas forms aerosols of tiny droplets. These reflect sunlight back into space, thereby cooling temperatures at ground level for up to 2 years, says Vincent Gauci of the Open University in Milton Keynes, England. Eventually, the sulfur dioxide combines with oxygen and water vapor in the atmosphere to form sulfate compounds, which return to ground level in acid rain.