Volcanic winter

A volcanic winter is a climate cooling caused by an extremely large volcanic eruption. Such an eruption releases ash and sulfur dioxide in huge quantities. They form aerosols of sulfuric acid. When they reach the stratosphere more sunlight is reflected, and some is absorbed by the stratosphere. These reactions heat up the stratosphere, but lead to a drop in the temperature on the ground.

The Siberian Traps, Emeishan Traps, and Deccan Traps are huge flood basalt provinces caused by volcanism. They are the cause, or part of the cause, of several mass extinctions, especially the Permian–Triassic extinction event.

Nuclear winter is a theory of similar effects which might be caused by a large-scale nuclear war.