CLIMATE

The Cold Snap in the Middle of the Thaw

~12,900 to 11,700 years ago

Phanerozoic · Cenozoic · Quaternary · Pleistocene · Late Pleistocene

Two thousand years into the warming that ended the last ice age, the North Atlantic fell back into near-glacial cold within decades and stayed there for more than a thousand years. Then it warmed again just as abruptly. Greenland ice cores date both turns to within a decade, a precision the climate record rarely allows.

Why it matters

Climate can turn over inside a single human lifetime, and this time it did so while people were already settling into the first villages. The usual explanation is a flood of meltwater weakening the North Atlantic circulation, but which route the water took, and whether there was enough of it, is still argued.

Dating & uncertainty

The dating is not the uncertain part: the annual layers in the Greenland ice fix both turns to within a decade. The cause is another matter. A meltwater flood remains the standard trigger, but the two candidate routes, the St Lawrence to the south or the Arctic to the north, weaken the circulation very unequally in models, and it is not known whether the flood carried enough water.

Sources

1. Bakke et al. (2009), Nature Geoscience · Rapid oceanic and atmospheric changes during the Younger Dryas cold period
2. Condron & Winsor (2012), PNAS · Meltwater routing and the Younger Dryas
3. Keigwin et al. (2018), Nature Geoscience · Deglacial floods in the Beaufort Sea preceded Younger Dryas cooling

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