The temperature of the earth’s surface depends largely on two minor constituents of the atmosphere: water vapor and carbon dioxide. They are transparent to the short-wave energy (light and near infrared) that comes from the sun, but opaque to most of the long-wave heat radiation that tries to return to space. This “greenhouse effect” traps heat and makes the earth’s surface considerably warmer than it would be if the atmosphere had no water vapor or carbon dioxide in it. An increase in either constituent would make it warmer still. Warm eras in the geological past may have been caused by CO2 from volcanoes.
At present the atmosphere contains 2.35 trillion tons of carbon dioxide, existing in equilibrium with living plants and sea water (which tends to dissolve it). Up to 1860, man’s fires added only about 500 million tons per year, and the atmosphere had no trouble in getting rid of this small amount. But each year more furnaces and engines poured CO2 into the atmosphere. In 1900, the amount was 3 billion tons. By 1950, it was 9 billion tons. By 2010, if present trends continue, 47 billion tons of carbon dioxide will enter the air each year. [actual 2010 emissions = 37 billion tons]
This will be only 2% of the total carbon dioxide, but if it is more than can be dissolved by the oceans or absorbed by plants or minerals, the concentration of CO2 in the atmosphere will tend to increase. The greenhouse effect will be intensified. Some scientists believe that this is the cause of recent warming of the earth’s climate. Dr. Revelle has his doubts.
In the future, if the blanket of CO2 produces a temperature rise of only one or two degrees, a chain of secondary effects may come into play. As the air gets warmer, sea water will get warmer too, and CO2 dissolved in it will return to the atmosphere. More water will evaporate from the warm ocean, and this will increase the greenhouse effect of the CO2. Each effect will reinforce the other, possibly raising the temperature enough to melt the icecaps of Antarctica and Greenland, which would flood the earth’s coastal lands.
Dr. Revelle has not reached the stage of warning against this catastrophe, but he and other geophysicists intend to keep watching and recording. During the International Geophysical Year (1957-58), teams of scientists will take inventory of the earth’s CO2 and observe how it shifts between air and sea. They will try to find out whether the CO2 blanket has been growing thicker, and what the effect has been. When all their data have been studied, they may be able to predict whether man’s factory chimneys and auto exhausts will eventually cause salt water to flow in the streets of New York and London.