Warming Earth?

CO2 may change world climate

Nature could hardly have created anything that seems more innocuous. An invisible and odorless gas, carbon dioxide is a simple molecular linkup of just a single atom of carbon and two atoms of oxygen (CO2). It constitutes a mere fraction of the atmosphere (.03% vs. about 78% for nitrogen and 20% for oxygen) but becomes dangerous to man and other air-breathing creatures when it accumulates in concentrations higher than 10% as, say, at the bottom of deep wells or mine shafts.

Yet CO2 is vitally important to the earth's wellbeing. A key ingredient in photosynthesis—the miraculous process by which green plants grow and produce oxygen—CO2 directly or indirectly sustains all terrestrial life. Now it appears that the gas may carry the potential for trouble as well. Accumulating in the atmosphere at an accelerating rate, carbon dioxide could significantly raise global temperatures by early in the next century and dramatically alter the quality of life. With such a prospect under study, a federal official says: "We have about ten years to come up with an answer."

As the density of CO2 increases, the gas acts somewhat like a one-way mirror. Rays of life-giving sunlight can pierce it, heating the surface of the earth. But when this heat is radiated back by the ground in the form of longer infra-red waves, it is screened by the CO2, which absorbs it, thereby raising its own temperature and that of the ground. This so-called greenhouse effect is dependent on the concentration of atmospheric CO2: the greater the amount, the warmer the earth may become.

There is nothing mysterious about the buildup of atmospheric CO2. All fires, from the smoky flames of cave dwellers to the searing hearth of a modern steel plant, produce CO2. It makes no difference whether the fire is fueled by wood, coal, oil or gas. The inevitable byproduct is always dumped into what scientists sardonically call the "sewer in the sky."

Enormous quantities of CO2 have been belched into the atmosphere since the start of the Industrial Revolution. But only recently has the increase become a cause of concern. In the past 20 years, it rose almost as much as it did in the century before. These measurements, made by the Scripps Institution of Oceanography atop Mauna Loa volcano on the island of Hawaii, are confirmed by similar readings at locations as far-flung as the South Pole, Alaska and Samoa.

Of the millions of tons of CO2 poured into the atmospheric sewer each day, about half apparently remains there. Still unclear is where the rest goes. The ocean provide a major natural "sink," soaking up much of its solution, as do the world's great forested zones, which sop up CO2 for photosynthesis.

But an increasing number of scientists maintain that the forests are being slashed and burned at a perilous rate. This is being done both to extend agriculture and, especially in the impoverished developing countries, to use the wood as a fuel. By desiccating and destroying the land, the ruthless felling of trees has still another harmful side effect: it exposes rich topsoil, or humus, and allows the escape of CO2 formerly trapped in it.