Warm Climate Surprises

摘要

Over the last decade, paleoclimatic data from ice cores and sediments have shown that the climate system is capable of switching between significantly different modes, suggesting that climatic surprises may lie ahead (1). Changes of several degrees inglacial surface air and sea temperatures over large expanses of the high northern latitudes apparently occurred multiple times within years to decades (2, 3) and have been attributed to abrupt shifts in oceanic thermohaline circulation (4). These high-latitude events are likely linked to abrupt climatic shifts at low latitudes (5, 6). Most attention in the growing area of abrupt climatic change research continues to be focused on the large changes observed during glacial periods, when large quantitiesof glacial meltwater were available to influence ocean circulation and climatic change. In contrast, the current warm inter-glacial climate is often characterized as relatively stable, leaving the impression' that climates of the future are likely to bemore or less well behaved. There also seems to be a widespread belief that the full range of natural interannual- to centennial-scale climate variability is well represented in the instrumental record of the last century. The weight of the paleoclimaticevidence now being collected, however, suggests that these comforting conclusions of benign warm climate variability may be incorrect.