Younger Dryas

The Younger Dryas (YD, Greenland Stadial GS-1) was the final climatic phase of the Last Glacial Period that occurred from around 12,900 to 11,700 years Before Present (c. 10,900 – c. 9,700 BC). 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 around 3 °C (5 °F) over North America, 2–6 °C (4–11 °F) in Europe and up to 10 °C (18 °F) in Greenland, in a few decades. Cooling in Greenland was particularly rapid, taking place over just 3 years or less. At the same time, the Southern Hemisphere experienced warming. This period ended as rapidly as it began, with dramatic warming over around 50 years, the transition from the glacial Pleistocene epoch into the current Holocene interglacial. The Younger Dryas onset was not fully synchronized; in the tropics, the cooling was spread out over several centuries, and the same was true of the early-Holocene warming. Even in the Northern Hemisphere, temperature change was highly seasonal, with much colder winters, cooler springs, yet no change or even slight warming during the summer. Substantial changes in precipitation also took place, with cooler areas experiencing substantially lower rainfall, while warmer areas received more of it. In the Northern Hemisphere, the length of the growing season declined. Land ice cover experienced little net change, but sea ice extent had increased, contributing to ice–albedo feedback. This increase in albedo was the main reason for net global cooling of 0.6 °C (1.1 °F). During the preceding period, the Bølling–Allerød Interstadial, rapid warming in the Northern Hemisphere was offset by the equivalent cooling in the Southern Hemisphere. This "polar seesaw" pattern is consistent with changes in thermohaline circulation (particularly the Atlantic meridional overturning circulation or AMOC), which greatly...