The Younger Dryas: What Caused the Big Freeze 12,900 Years Ago?

An abrupt return to near-Ice Age cold about 12,900 years ago, and one of the most debated events in prehistory.

The Younger Dryas was a sudden cooling in the Northern Hemisphere that began about 12,900 years ago and lasted around 1,200 years, before an abrupt warming about 11,700 years ago.

The Younger Dryas is a period of sudden cooling in the Northern Hemisphere that began about 12,900 years ago and lasted around 1,200 years. The world had been warming out of the last Ice Age when, within a short time, temperatures in Greenland and the North Atlantic dropped back toward glacial levels. It is named after Dryas octopetala, an Arctic flower whose pollen shows up in European lake sediments from this time.

The end was even more abrupt than the start. Greenland ice cores show that around 11,700 years ago temperatures there rose by many degrees within a few decades or less. That date marks the start of the Holocene, the warm period in which farming and civilization arose. Göbekli Tepe was being built soon after.

The most widely accepted explanation is that meltwater from the shrinking North American ice sheets poured into the North Atlantic and weakened the ocean circulation that carries heat north. In 2007 a group of researchers proposed instead that a comet or its fragments exploded over the ice sheet, triggering fires and cooling. This Younger Dryas impact hypothesis has been heavily criticized, with many studies failing to replicate its markers.

Popular writers such as Graham Hancock link the Younger Dryas to flood myths and to Plato's date for the sinking of Atlantis, about 9600 BCE, which falls near its end. Most scientists regard that link as coincidence, but the event itself is real and dramatic. Its causes and effects on early human communities remain an active field of research.