Science: Warming Earth?

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Yet by far the most significant factor in the accumulation of CO2 is the burning of fossil fuels. Especially worrisome is the Carter Administration's choice of coal as the U.S.'s great energy hope. Unlike competing nuclear power, which gives off no CO2, coal will inevitably add to a buildup of the gas, as will the increased consumption of other fossil fuels. A National Academy of Sciences study panel warns that if the use of coal proceeds along the Administration's projections, atmospheric concentration of CO2 might reach four to eight times that of the pre-industrial level by the year 2150. That, predicts the panel, could produce an increase in the global mean air temperature of more than 6° C (11° F.)—creating climatic conditions that the earth has not seen since the age of the dinosaurs more than 70 million years ago.

Even if the hike in temperature were smaller—say only a degree or so—the effects might not be minor. Applied year round to the entire earth, such an increase could shift whole forests, grasslands and deserts. At the polar regions, enough ice could melt to elevate sea levels by as much as 5 m (16 ft.). That would eventually inundate low-lying coastal areas round the world, including parts of The Netherlands and the Atlantic seaboard.

There would be some benefits, to be sure. Heavier rainfall would possibly restore Africa's extremely dry Sahel, the Sahara and the Arabian desert to their ancient fertility and make vast tracts in Siberia and Canada suitable for growing cereal grains. But the rich wheat and corn belt in the central U.S. would probably become too dry for these crops. Hundreds of millions of people might suffer from these dislocations.

Still, scientists are by no means certain that nature will follow their scenarios. The earth's climate is the product of such a complex mix of factors that it becomes impossibly difficult to isolate just one. For example, climatologists do not yet know the exact role of atmospheric dust. Dust can cool the earth by screening out warming sunlight, as has been noted after major volcanic eruptions like that of Krakatoa in 1883, yet also act as an atmospheric cap keeping in heat. Says Scripps' Charles Keeling: "Dust impedes radiation in both directions. We do not know if the net effect is heating or cooling." No less puzzling is the possible effect on world temperature of changes in the atmosphere's ozone layer.

There is another wrinkle in these climatological complications. For about two decades ending in the early 1970s, the earth was in what seemed to be a cooling phase. Some climatologists suggested that the chill marked the beginning of a "little ice age," like the one that persisted in Europe from about 1550 to 1850. If they are right, then the cooling forces—which could be attributable to anything from increased atmospheric dust to subtle changes in the amount of heat received from the sun—will be pitted against the warming force of the so-called greenhouse effect. For a while, at least, these two opposites might balance each other neatly.