ENVIRONMENT

A Sudden Return of the Cold

~12,900 years ago

Palaeolithic · Upper Palaeolithic · Last glacial

Two thousand years into the warming that was ending the ice age, the North Atlantic world snapped back to near-glacial cold in decades, and stayed there for over a millennium. The favoured culprit is a flood of glacial meltwater, traced through the Mackenzie River to the Arctic, that freshened the ocean and stalled the currents carrying heat north. Around 12,900 years ago the warmth failed; around 11,700 it returned, even faster.

Why it matters

The Younger Dryas is the demonstration that climate does not always drift, it can lurch: a hemisphere rearranged within a human lifetime. It struck exactly when villages like those of the Natufians had settled onto wild harvests, and the return of warmth opens the chapter in which farming begins. It is also the standing warning attached to today's ocean currents: they have switched off before.

Dating & uncertainty

Ice cores place the onset at 12,870 +/- 30 years before 1950, astonishing precision for a prehistoric event. The trigger is still argued: the standard account is a flood of glacial meltwater freshening the North Atlantic, with sediment evidence pointing down the Mackenzie River to the Arctic; a comet impact and volcanism have been proposed as alternatives, and the platinum spike once read as impact debris may itself be volcanic.

Sources

1. Keigwin et al. (2018), Nature Geoscience · Deglacial floods in the Beaufort Sea preceded Younger Dryas coolingdoi:10.1038/s41561-018-0169-6
2. Warken et al. (2025), Science Advances · Discovery of Laacher See eruption in speleothem record synchronizes Greenland and central European Late Glacial climate changedoi:10.1126/sciadv.adt4057
3. Green et al. (2025), PLOS One · A possible volcanic origin for the Greenland ice core Pt anomaly near the Bolling-Allerod/Younger Dryas boundarydoi:10.1371/journal.pone.0331811

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