CLIMATE

The Younger Dryas

~12,900 to 11,700 years ago

Phanerozoic · Cenozoic · Quaternary · Pleistocene · Late Pleistocene

The North Atlantic returned to near-glacial cold within decades about 12,900 years ago, two thousand years into the warming that ended the ice age, and stayed cold for more than a thousand years.

The Younger Dryas is an abrupt return to near-glacial cold that came two thousand years into the warming that ended the last ice age. The North Atlantic cooled within decades, remained cold for more than a thousand years, then warmed again just as abruptly. Researchers generally explain the cooling by a weakening of the Atlantic meridional overturning circulation. This system of currents carries warm surface water north and returns cold water at depth, and it stalls when enough fresh water dilutes the surface water. Ice cores, cylinders of ice drilled from the Greenland ice sheet, allow the cooling and the warming to be dated each to within a decade. Past changes of climate can rarely be dated that precisely.

Why it matters

Climate can reverse within the span of a human life. It did so during the Younger Dryas, at a time when human populations were already settling into the first villages.

Dating & uncertainty

The dating is established: the annual layers of the Greenland ice allow researchers to place the start and the end of the cold period each to within a decade. The cause is less certain. The trigger that researchers retain is a flood of meltwater, the fresh water from melting ice. Two routes are considered for that flood, the St Lawrence to the south or the Arctic to the north. In models, the two routes weaken the Atlantic meridional overturning circulation very unequally, and the volume of water available is not established.

Earth history as one day

23:59:59.75245 ms before midnight

if Earth’s 4.54 billion years were compressed into a single day