Longer term, sulfur from volcanoes has the potential to cool the Earth [1]. Sulfur reacts with water in the air to form sulfuric acid droplets that reflect sunlight hitting Earth, thus blocking some rays. The reduction in sunlight can reduce temperatures for a year or so, until the droplets fall out of the atmosphere. When Mount Pinatubo erupted, it cooled the planet by 0.9 degrees Fahrenheit.