Author(s): John C. Moore
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Abstract: Two deep ice cores (GRIP and GISP2) have been recently recovered from the Summit area of central Greenland. Unlike the long Vostok ice core from Antarctica, the Greenland ice can be dated with almost annual precision down to about 50,000 years. During the last glacial stage the cores show large, abrupt climate changes corresponding to temperature changes of about 5°C. The changes are likely to reflect at least regional scale variations and suggest that the climate of the North Atlantic region is able to switch climate modes in times as short as decades. Each climate mode is stable for periods as long as thousands of years or for times as short as a hundred years. Such rapid changes suggest the importance of the atmospheric and oceanic circulation systems. The agreement between the two cores which are separated by 30 km is remarkable, with all the climatic changes recorded in both cores. The older ice, from the deepest 10% of the cores near bedrock has suffered various disturbances as a result of ice flow and the inhomogeneous mechanical properties of ice from different climate periods. The interglacial ice also shows evidence of similar dramatic climate changes to those observed in the glacial ice. These findings are in marked contrast to the present climate which appears to have been remarkably stable for the last 8,000 years, indeed there is probably no period of stable climate in the last 150,000 years that exceeds 2,000 years in duration. The last interglacial is known to have been slightly warmer than the present one, its unstable climate raises questions about our own future climate in the light ofcurrent theories of greenhouse warming. All GeM model predictions offuture climate predict the largest changes in temperatures will occur in the northern regions around latitudes 70oN. It is likely that winter temperatures are most likely to be raised. However no GeM models predict the very rapid switches in climate that are observed in the Greenland ice cores. Similarly due to the great stability of the current climate, there are no historical records ofabrupt climate shifts from which predictions of future climate can be made.
Year: 1994