Longer term, sulfur from volcanoes has the potential to cool the Earth. 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.
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