Temperature variations inferred from analyzing oxygen isotope records in ice cores retrieved from Greenland and Antarctica have demonstrated that periods of extremely rapid global climate change have occurred in the Earth System during the last glacial cycle. The period from 60,000 to 30,000 years ago (Marine Oxygen Isotopic Stage 3) is, in particular, characterized by high northern latitude quasi-periodic millennial scale fluctuations in annually averaged temperature of 10°C to 15°C. These saw-toothed shaped temperature variations are known as Dansgaard-Oeschger (D-O) oscillations. I will describe some of the dynamical mechanisms that may explain the nature of the oscillations including some numerical modelling results of the D-O phenomenon.