An
impact winter is a period of prolonged cold weather due to the impact of a large
asteroid or
comet on the Earth's surface. If an asteroid were to strike land or a shallow body of water, it would eject an enormous amount of dust, ash, and other material into the
atmosphere, blocking the
radiation from the sun. This would cause the global temperature to decrease drastically. If an asteroid or comet with the diameter of about or more were to hit in a large deep body of water or explode before hitting the surface, there would still be an enormous amount of debris ejected into the atmosphere. It has been proposed that an impact winter could lead to
mass extinction, wiping out many of the world's existing species.