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.

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 6DEG C (11DEG 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.

But if the burning of fossil fuels continues to increase at an annual rate of 3% to 4%, as scientists like Stephen Schneider of the National Center for Atmospheric Research consider likely, then the greenhouse effect may well prevail. In that case, it will be a hot time on earth. And once the warming has taken place, even if all discharges of CO2 into the atmosphere could be abruptly halted, it would take centuries for the excess gas to be absorbed by the oceans and dwindling forests.

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