The Younger Dryas was a period in Earth's geologic history that occurred circa 12,900 to 11,700 years Before Present. It is primarily known for the sudden or "abrupt" cooling in the Northern Hemisphere, when the North Atlantic Ocean cooled and annual air temperatures decreased by ~3 °C over North America, 2–6 °C in Europe and up to 10 °C in Greenland, in a few decades. From Wikipedia
