The Younger Dryas
The Ice Age snapped back for 1,200 years, almost overnight
About 12,900 years ago, with the glaciers already retreating, the Northern Hemisphere abruptly cooled, by up to 10 °C in Greenland within a few years. The cold lasted some 1,200 years and ended just as suddenly, within about fifty; its end opened the Holocene, the warm epoch in which farming began.