The danger that the earth's atmosphere may be heating up to catastrophic levels from atmospheric pollution is greater, and the heating may occur much faster than previously thought, according to new research by several groups of scientists.
In the past few weeks several new reports have given new evidence that the warming is actually occurring and that the danger is not only from one polluting gas, but also from several more.
Until now, scientists thought the danger of turning the atmosphere into an unregulated oven that would melt ice caps, flood coastal regions, and create deserts in the next century was chiefly from carbon dioxide caused by industrial and auto combustion.
But now in reports from the Goddard Space Flight Institute and elsewhere, at least five other gases have been found that as a group may be heating up the atmosphere as much or more than carbon dioxide. They are nitrous oxide, methane, ozone, and two forms of freon.
The total effect may bring the serious problems of heating 20 years closer, says Gordon MacDonald, chief scientist at Mitre Corp. and one of a group of researchers studying the problem. The heating from "trace gases" in the atmosphere may cause the worst problems just 40 years from now rather than 60, he says.
At the same time the danger from other gases is being calculated, there may be confirmation that the atmosphere is actually beginning to heat up. None of the conclusions is yet firm because, as MacDonald said, "of the difficulty of finding a trend in something global temperature that is always going up and down."
But George Kukla and Joyce Gavin of Columbia University recently reported that the amount of pack ice in Antarctic summers is sharply lower now than in the 1930s. The finding agrees with the prediction that the first notable effect of warming air would be along the edge of the seasonally shrinking sea ice.
Kukla wrote that only tentative connections can be made between his results and atmospheric warming, but that priority must be given to such studies now.
From recent measurements of four of the gases--methane, nitrous oxide, and the two types of freon--James Hansen and his colleagues at the Goddard Space Flight Center in New York now say that these gases alone may cause as much heating of the atmosphere as the better-documented threat from carbon dioxide.
Hansen and his colleagues wrote in the current issues of Geophysical Research Letters that this warming along with that from carbon dioxide should push the global temperatures above their natural up-and-down swings very soon, sometime within this decade.
The other problem gas is ozone, which may have an effect one-third that of carbon dioxide, MacDonald says. Ozone is increasing largely because a chemical that normally combines to destroy it in the atmosphere is being depleted by car and industrial exhaust fumes.
All the chemicals, from carbon dioxide to ozone, would warm the planet in the same way. They let the sun's light into the atmosphere, but stop some wavelengths of warming radiation from escaping the atmosphere. They absorb the radiation and return much of it back to the atmosphere, creating the effect of a thickening blanket over the planet as all the pollutants steadily increase.
The source of several of the agents believed to be warming the atmosphere is global industrialization. This is the cause of increased burning of fossil fuels, which produces carbon dioxide, and increased use of gases such as freon in refrigerators and aerosol sprays.
Several other sources are more natural. The chief source of methane in the air is from decaying matter in swamps, animal waste, and "flatulent cattle add a lot," MacDonald says. Nitrous oxide comes from the use of fertilizers, and from burning wood in man-made or natural fires.
MacDonald said all the evidence so far does not conclusively demonstrate that severe warming of the earth will happen, but the signs are serious enough to warrant real concern.