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There is some evidence that the earth had cooled down—at least temporarily—in the 1950s and 1960s. In 1972, according to German Climatologist Horst Dronia, the atmosphere in the Northern Hemisphere was one full degree centigrade colder than in 1949. But there have been indications of a slight warming since then. If the cooling-theory school is correct, however, the prospects for man are chilling. A global average temperature drop of only 1° could shorten the growing seasons in the temperate zones by a critical week or more and reduce food supplies. Increased heating requirements would put a further strain on energy sources.
Other climatologists believe that any long-term cooling trend is being offset by a "greenhouse effect," caused by an increasing atmospheric content of carbon dioxide produced by the burning of fossil fuels. The CO2 prevents some of the heat radiated by the earth's surface from escaping out into space, thus warming the planet's atmosphere. Warming-trend advocates note that winters in such normally chilly regions as Scandinavia and New England have been uncharacteristically mild in recent years, and glaciers in the Alps have actually retreated. Even a modest rise in world temperatures would bring with it other perils. Ocean levels raised by melting polar ice could drastically change global air-circulation and rainfall patterns, as well as cause extensive flooding. The result could be a radical decline in the productivity of many of the world's important agricultural regions.
Climatologists tend to agree that whatever the long-term trend, the earth's climate is entering a period of increased variability that will make prediction and planning ever more difficult. "I do not see glacial melts or an ice age," says Jerome Namias of the Scripps Institution of Oceanography in La Jolla, Calif. "What I see is fluctuations." Stephen Schneider, deputy head of the climate project at the National Center for Atmospheric Research in Boulder, Colo., says the evidence of the past few years suggests that there is a good possibility the climate is becoming more unpredictable.
To learn more about these fluctuations, an international consortium of scientists is compiling a record of the earth's climate. Climatologist Lamb and his colleagues have assembled an accurate historical record of the seasons going back as far as 1400 A.D.—based on parish registers, government documents, monastery records, and such physical evidence as sediment deposits in lakes and growth rings in trees. Says Lamb: "The more we know about cycles of the past, the better we can work with the highly detailed and sophisticated observations we have of our weather today." Geophysicist Willi Dansgaard of the University of Copenhagen is studying cores taken from the ice in Greenland and Antarctica to learn about temperature and precipitation through the ages. Researchers at Columbia University's Lament-Doherty Geological Observatory are examining sea-floor cores for clues to ocean temperatures and circulation.