Younger Dryas

The Younger Dryas, from c. 12,900 to c. 11,700 calendar years ago (BP), was a sharp decline in temperature over most of the northern hemisphere, at the end of the Pleistocene epoch, immediately preceding the current warmer Holocene. It was the most recent and longest of several interruptions to the gradual warming of the Earth's climate since the severe Last Glacial Maximum, c. 27,000 to 24,000 calendar years BP. The change was relatively sudden, taking place in decades, and resulted in a decline of 2 to 6 degrees Celsius, advances of glaciers and drier conditions, over much of the temperate northern hemisphere. It is thought to have been caused by a decline in the strength of the Atlantic meridional overturning circulation, which transports warm water from the equator towards the North Pole, and which in turn is thought to have been caused by an influx of fresh cold water from North America into the Atlantic. The Younger Dryas was a period of climatic change, but the effects were complex and variable. In the southern hemisphere, and some areas of the north such as the south-eastern United States, there was a slight warming.