The underlying theory is that regional and global climate systems are like other complex systems - they can adjust only so far to accommodate new factors such as increased atmospheric carbon dioxide and the associated greenhouse effect. When such a system approaches the threshold at the outside edge of its adjustment capabilities, it may fluctate wildly. Then it fragments and reorganizes into a new stable regime. While the flip re-establishes a state of decreased fluctations, the new regime may be very different from its predecessor. The fear in climate change circles is that the increasingly frequent extreme weather events we are seeing now may be a sign that our climate system is already nearing its threshold and a rapid climate flip may be just ahead.
Historical evidence supporting such a possibility comes from ice core research.
Like tree rings, ice cores provide yearly evidence of some environmnetal conditions. Snow and therefore ice accumulation is lower in cold periods in Greenland. The warming at the end of the last glaciation was characterized by a series of abrupt returns to glacial climate, of whichthe best known is the Younger Dryas event, which endedapproximately 10,000 years ago. Apparently it ended very quickly. Results from the Greenland ice core GISP2 indicate that the transition from the cold Younger Dryas period to the subsequent Preboral period occured in one to three years during which snow accumulation doubled.