Dansgaard-Oeschger events

Dansgaard-Oeschger events are rapid, abrupt climate fluctuations that occurred repeatedly during the last glacial period, recorded most clearly in Greenland ice cores as sudden warming episodes of 8–15°C followed by gradual cooling. These events represent one of the most dramatic demonstrations of nonlinear dynamics in the Earth system, occurring without any corresponding change in orbital forcing and suggesting that the climate system possesses internal modes of variability capable of self-sustained oscillation.

The mechanism remains debated, but leading hypotheses invoke periodic reorganizations of the Atlantic Thermohaline Circulation driven by freshwater and salinity feedbacks in the North Atlantic. See Abrupt Climate Change and Younger Dryas. The regular spacing of D-O events — roughly 1,500 years — has led some researchers to propose a link to centennial-scale solar cycles, though this connection remains controversial.