A massive explosion at the South Pole on September 13, 2000 which caused the Earth to tilt on its axis, triggering tsunamis, floods, volcanic eruptions, famine, civil war, and disruptions to virtually every eco-system on the planet. The entire continent of Antarctica is destroyed, and half of the world's human population is lost.
The Second Impact is believed to have been the greatest disaster since the First Impact (also referred to as the 'Giant Impact') about four billion years ago, during which a rogue planetoid named Theia struck the Earth, causing the formation of the Earth's Moon.
To the public, the cause of the Second Impact was explained as a 4-inch meteorite traveling at 95% of the speed of light (too small and too fast for detection) impacting Mount Markham in Antarctica. In truth, the event was a direct result of SEELE's experiments on a being called Adam, the First Angel, which they found inside a subterranean cavity called the White Moon at the South Pole.
Guided by the Dead Sea Scrolls, SEELE sought to minimize the potential damage of the Angels by reverting Adam into an embryonic state. Although they succeeded, the massive release of energy during the process resulted in the global disaster known as the Second Impact.
As a result of the Second Impact, weather patterns around the world were severely affected, causing Japan to loose its seasons.
Based on Neon Genesis Evangelion Platinum: 06 DVD Booklet