| Popis: |
According to the astronomical theory of climate, variations in the earth’s orbit are the fundamental cause of the succession of Pleistocene ice ages. This paper summarizes how the theory has evolved since the pioneer studies of James Croll and Milutin Milankovitch, reviews recent evidence that supports the theory, and argues that a major opportunity is at hand to investigate the physical mechanisms by which the climate system responds to orbital forcing. After a survey of the kinds of models that have been applied to this problem, a simple, time-dependent model is discussed that simulates the history of planetary glaciation reasonably well over the past 250 000 years. Ignoring anthropogenic and other possible sources of variation acting at frequencies higher than one cycle per 19 000 years, this model predicts that the long-term cooling trend which began some 6 000 years ago will continue for the next 23 000 years. |
