Science: Another Ice Age?

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The arrival of another ice age has long been a chilling theme of science fiction. If the earth's recent history is any clue, says Marine Geologist Cesare Emiliani of the University of Miami, a new ice age could become a reality.

Writing in Science, Emiliani reports that the earth has undergone at least eight periods of extreme cold and seven of torrid heat in the past 400,000 years. His conclusion is based on cores of ocean sediment from the Caribbean. Composed of the remains of tiny sea animals, the layered sediment provides a record of climatic changes. When the oceans warm up, there is a decrease in the ratio of the isotope oxygen-18 to ordinary oxygen in the shells of the little creatures; when temperatures go down, the concentration of oxygen-18 goes up. Moreover, the proportions are preserved after the creatures die and sink to become layers of sediment. Thus, because these layers can now easily be dated, the shells can be studied to establish past temperature trends.

Scientists once held that there were four ice ages, each as long as 100,000 years, separated by warm periods of at least comparable duration. But Emiliani's investigations, and also those of Columbia University's David Ericson and Goesta Wollin, have shown that the ice ages were as short as 10,000 to 20,000 years. Moreover, Emiliani says, the climatologically comfortable intervals between them were also geologically brief. Thus, Emiliani warns, the present period of "amiable climate," which has already lasted 12,000 years, may soon come to an end, perhaps within the next 2,000 or 3,000 years.

In what direction will the earth's climate then turn? Emiliani refuses to speculate. But if man continues his "interference with climate through deforestation, urban development and pollution," says Emiliani in typical scientific jargon, "we may soon be confronted with either a runaway glaciation or a runaway deglaciation, both of which would generate unacceptable environmental stresses."