| Summary: | During the last decades, there is an increasing concern about global climate change as a consequence of anthropogenic influences. Recently, a report presented by the working group of the Intergovernmental Panel on Climate Change (IPCC) concluded that there is convincing evidence that most of the warming observed over the last 50 years is the result of human activities. The working group also predicts that climate will continue to change throughout the 21st century, due to human influence, such as the emission of greenhouse gasses. Clearly, it is essential to understand the natural variability of global and regional climate change to discriminate and quantifY man-induced changes. Long records ofpast changes in climate offer a key role in identifYing the effects of anthropogenic influences and climate models used for predicting global climate change in the future should also be able to reconstruct and 'predict' past climate changes (Barron et al., 1995). The conclusions put forward by the IPCC are based on measurements of temperature and on climate proxy data for the Northern Hemisphere over the last 1,000 years inferred from e.g. tree rings, corals and ice cores. Of course, longer-term natural climate variations also occur as demonstrated in studies of Pleistocene records. Studies of Pleistocene climate records from ice cores, corals, varves and deep-sea sediments show that the Earth's climate has varied on a millennial scale with periods of several thousand years (Pisias et ai., 1973; Dansgaard et ai., 1984; Pestiaux et ai., 1988; Bond et ai., 1997). Millennial-scale climate cycles are also present in the older part of the Pleistocene (Oppo et ai., 1998; Raymo et ai., 1998; McManus et ai., 1999) and in the Pliocene (Steenbrink, 2001). The origin of these cycles, however, is not well understood and may be attributed to internal forcing mechanisms of the climate system (e.g. ice-sheet dynamics and atmosphere-ocean interactions) or to external mechanisms (e.g. solar variability, long-term tidal variations and ...
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