关于冰期成因问题的探讨

在地质历史上曾出现过几次大冰期。其中最近的两期都是全球性的,时间也比较确定。它们是第四纪大冰期(发生在近二百万年)和晚古生代大冰期(距今约2-3亿年)。在每一次大冰期中,又可分为几个冰期和间冰期。在大冰期之间是非冰期。关于气候变迁的原因或冰期的成因问题,在科学界至今还是一个“谜”。虽然前人曾提出过各种各样的理论,但是正如李四光(1972)和施瓦茨巴克(Schwarzbach,1974)等所指出的:这些论点都不足以说明气候变迁的原因或冰期的成因问题。近几十年来,大量新的科学资料的积累,尤其在海洋研究方面所取得的进展,为这个问题的解决提供了素材。

ON THE CAUSES OF ICE AGES

Between the Permo-Carboniferous glaciation and the Quaternary glaciation, the climate had three characteristics:1. Throughout the world the average annual temperature was higher than that of today at the same latitude.2. The temperature range between high and low latitudes was smaller than that of today.3. The average annual temperature range was also smaller than that of today. Prom the Permo-Carboniferous glaciation to the Jurassic the climate throughoutthe world gradually turned warmer and the above mentioned two temperature ranges became shortened gradually; but from the Jurassic to the present day the climate turned again cooler gradually and the temperature ranges gradually enlarged, although such changes were marked by a number of fluctuations.A lot of theories of the Ice Ages have been proposed to explain these unusually marked climatic changes, but all of them are very insecurely founded. The climatic changes of the earth could be explained best by the variation in the obliquity of the earth’s ecliptic(ε).Planets of the solar system very greatly among themselves in the obliquity of ecliptic. The obliquity of the earth has probably changed greatly during its evolution. The computed values have shown that:1. When the obliquity is 10°, the corresponding average annual temperature, the temperature range between high and low latitudes and the average annual temperature range throughout the world are in agreement with the Jurassic climatic conditions. Hence an obliquity of 10° is inferred for the earth during the Jurassic.2. When the obliquity Changes from 23° to 10°, the corresponding climatic conditions would be like those existing from the Permo-Carboniferous glaciation to the Jurassic.3. When the obliquity changes from 10° to 23°, the corresponding climatic conditions would resemble those occurring from the Jurassic to the present day.In the earth’s history there were at least two types of variation in the obliquity of the earth’s ecliptic.1. The obliquity reached a maximum amplitude of 10° to 15° within an average period of 200 to 300 m.y.2. The obliquity fluctuated with a small amplitude of 2° to 3° within an average period of 410,000 years. The overlapping of the great and the small fluctuations represents the law of the variation of the obliquity in the earth’s history. It is the great fluctuation that had caused the alternation of Glaeiation and Nonglaciation. It is the small fluctuation that had caused the alternation of the Glacial period and the Interglacial period during the Quaternary glaciation. I am convinced that the variation of the earth’s obliquity has been the most important, though not the exclusive, cause of the climatic changes, i.e. the Ice Ages.