The Pattern of Dansgaard-Oeschger Events

Randall introduces Dansgaard-Oeschger events - rapid climate fluctuations that are among the most dramatic and least publicly discussed features of the last glacial period. These were not gradual shifts. They were sudden, sharp reorganisations of the climate system, occurring 25 times across the last ice age and leaving a clear signature in the Greenland ice cores where they were first identified.

The pattern of each event follows a consistent structure. An abrupt warming phase unfolds over just a few decades - geologically instantaneous - followed by a prolonged cooling period that can last several centuries or even millennia before the next warming pulse arrives. Some researchers have identified a quasi-periodic recurrence interval of approximately 1,470 years between events, though Randall notes this remains debated. Their Holocene equivalents are known as Bond events, suggesting the same underlying mechanism has continued operating into the present interglacial period.

Randall uses this framework to sharpen the distinction around the Younger Dryas. Dansgaard-Oeschger events involve rapid warming followed by slow cooling. The Younger Dryas was the opposite - an extremely rapid cooling event that interrupted the warming trend following the last glacial maximum. Understanding what makes the Younger Dryas anomalous within the broader pattern of glacial climate instability is, for Randall, essential context for the larger question of what caused it - and whether the mechanism responsible is something that could operate again.

Join Randall for his upcoming Finger Lakes Tour, Aug 30 Sep 5, 2026