The end of the present interglacial: How and when?

Despite the large decline in Northern Hemisphere summer insolation during the last 8000 years, neither sea level nor polar temperatures have as yet undergone any significant downturn. This behavior is consistent with the prediction by Kukla and Matthews (1972) that the Holocene interglacial will terminate suddenly with a jump to another of the climate system's modes of operation. This is what happened at the end of the last period of peak interglaciation. However, complicating the situation is evidence that ice sheet growth during the transition from marine stage 5e to 5d preceded the shut down of the Atlantic's conveyor circulation which is thought to have brought Europe's Eemian to a close. If so, then in the natural course of events, the end of the present interglaciation awaits the onset of ice cap growth. However, it must be kept in mind that the ongoing buildup of greenhouse gases may alter the natural course of events. In particular, the warming and wetting of the planet will gradually reduce the density of surface waters in the regions where deep waters form. As this reduction is not likely to be symmetrical between the northern Atlantic and the margin of the Antarctic continent, the current near balance between deep water production in the north and south may be disrupted causing an abrupt reorganization of the ocean's thermohaline circulation. Based on the paleoclimatic record, such a reorganization would have had a profound impact on the planet's climate. (C) 1998 Elsevier Science Ltd. All rights reserved.