ENVIRONMENT
The Younger Dryas
~12,900 years ago
Palaeolithic · Upper Palaeolithic · Last glacial
About 12,900 years ago, around the North Atlantic, the warming at the end of the ice age reversed within decades, and the region returned to cold for a millennium.
The Younger Dryas is a cold climatic episode that occurred about 12,900 years ago, two millennia after the beginning of deglaciation, and whose name derives from the eight-petalled mountain avens, Dryas octopetala, an arctic plant whose pollen marks this horizon in European sediments. The North Atlantic world returned within decades to conditions close to those of the glaciation, and maintained them for more than a millennium. The explanation most widely retained is an influx of meltwater, whose sediments follow the Mackenzie route to the Arctic. The mechanism runs through density: the circulation transporting heat northwards depends on the sinking, at high latitudes, of cold salty water denser than that beneath it; light meltwater does not sink, and the circulation slows. Warming resumes around 11,700 years ago, more rapidly still.
Why it matters
The episode establishes that climatic change may be abrupt rather than gradual and may reorganise a hemisphere within a human lifetime. It occurs while sedentary communities in the Levant were living on wild harvests, and the return of warming opens the period in which agriculture appears. It constitutes, finally, the precedent to which present-day monitoring of Atlantic ocean circulation refers.
Dating & uncertainty
Ice cores place the transition at 12,870 ± 30 years before 1950. The trigger remains debated: the principal hypothesis is a meltwater outburst freshening the North Atlantic, with sediments indicating the Mackenzie route; an extraterrestrial impact and a volcanic origin have been proposed, the platinum spike long interpreted as impact debris possibly being volcanic.
Our species’ history as one day
23:01:0158 min 58 s before midnight
if the 315,000 years of Homo sapiens were compressed into a single day