The last glacial period showed millennium scale climatic shifts between two different stable climate states. The state of thermohaline ocean circulation probably governs the climate, and the triggering mechanism for climate changes is random fluctuations of the atmospheric forcing on the ocean circulation. The high temporal resolution paleoclimatic data from ice-cores are consistent with this picture and a bi-stable climate pseudo-potential can be derived. It is found that the fast time scale noise forcing the climate contains a component with an &agr;-stable distribution. As a consequence the abrupt climatic changes observed could be triggered by single extreme events. These events are related to ocean-atmosphere dynamics on annual or shorter time scales and could indicate a fundamental limitation in predictability of climate changes. ¿ 1999 American Geophysical Union