DESERTIFICATION OF MID-LATITUDE NORTHERN ASIA AND GLOBAL CHANGE PERIODICITY IN THE QUATERNARY

摘要

The knowledge of the history of regional geosystems and prediction of their future evolution trends are indispensable for nature conservation. Global warming threatens to become catastrophic and is thus an urgent scientific and social problem. The last century of the past millennium was marked by an exceptional growth of global air temperature which became 0.6°C higher than at the end of the Little Ice Age (1550-1850). Warming was especially rapid after the 1960s, with a linear trend of 0.20°C per decade (global) and 0.29°C per decade in the Northern Hemisphere (Grusa et at., 2001). The past decade was the warmest over the millennium, and 1998 was the globally warmest year. Arctic ice sheets in warm season have reduced in surface area for 10-15% and have become 40% thinner for the past 50 yr. Mountain glaciers in Asia have been reducing and permafrost has been degrading. Scientists are not unanimous about the prospects, some believing that warming-related global change can speed up and cause regional- and global-scale socioeconomic ill effects, and others considering the problem ambiguous and poorly understood; the latter opinion is that prediction has even increased in uncertainty lately instead of being resolved (Boehmer-Christiansen, 2000). Prediction for global change and its short-term consequences is difficult because the changes are driven by sophisticated interplay of numerous climate controls and feedback mechanisms, while the available field and modeling data remain insufficient. The relative contributions of natural and cultural effects to the ongoing warming have not been so far constrained unambiguously.