TRENDS IN GLOBAL CLIMATE CHANGES INFERRED FROM GEOLOGICAL DATA

Abstract

Recent paleoclimatic data reveal the following trends in climate changes. (1) During three billion years, characteristic of the Earth was gradual global cooling with the increasing frequency, duration and scale of glaciations. Based on these features, three principal climatic stages can be defined in geological history: (a) non- glacial (Early Archean), (b) with episodic glaciations (Late Archean-Middle Riphean), and (c) with frequent peri- odical glaciations (Riphean-Recent). (2) Irreversible climate changes were complicated and disguised by numer- ous superimposed temperature fluctuations of different periodicity and amplitude. In the Phanerozoic, a hierarchy of subordinate climatic fluctuations of 10-12 ranks, from extremely long (few hundreds million years) to short- term (tens years long only) is defined. Signs of climatic fluctuations of two-three highest ranks are recognizable in Proterozoic glacial sections. (3) The hierarchy of climatic fluctuations was stable during the Phanerozoic at least. (4) Amplitudes of climatic fluctuations depended on the cophasing degree of elementary climatic oscillations and character of their feedbacks in the biosphere. (5) The warm non-glacial climate prevailed during the Precam- brian and Phanerozoic and was characteristic of 90% of the Phanerozoic and 95% of the post-Archean geological history. (6) Many climatic fluctuations, all those of first rank included, were of a global scale, synchronous, and cophasal. (7) Regional climate changes were caused by paleogeographic factors. (8) Global climate changes resulted in transformation of the latitudinal climatic zonality. The notion "global climate" is introduced to charac- terize the type of a planetary climatic zonality. Macrogeographic factors transformed latitudinal climatic belts into sublatitudinal ones. (9) Two main types of global climate (non-glacial and glacial) are defined. Transitions from non-glacial to glacial climate and vice versa were accompanied by rapid qualitative zonality reorganizations. (10) Each type of global climate is subdivided into gradations. (11) A peculiar feature of the global climate was an asymmetric position of climatic belts relative the equator. The asymmetry, which was insignificant during the non-glacial periods, and substantially increased at the time of glaciations, particularly of the great ones.