A NEW STUDY advocating greatly increased reliance on coal airily dismissed the consequences of the increased carbon dioxide that would result. Coal produces 25 percent more carbon dioxide per unit of energy produced than oil, and 75 percent more than gas, and coal-based synthetic fuels produce even more than that. But the World Coal Study report called for a tripling of coal use by the year 2000. "Present knowledge of possible carbon dioxide effects on climate," it concludes, "does not justify delaying the expansion of coal use." If and when effects of carbon dioxide become apparent, global fossil fuel use can be "reassessed."

As it happens, the National Academy of Sciences has just completed a somber study of the social and political implications of carbon dioxide increase. Because of its likely effects on climate, increased amounts in the atmosphere might not only disrupt agriculture and raise sea level by 15 to 20 feet. The increase could also widen the economic gap, and thus exacerbate the political gap, between the industrialized countries and the developing nations of the Third World.

Rapid climate change -- faster than anything human society has yet experienced -- is a distinct posssibility. Increased amounts of carbon dioxide could mean that "by the middle of the next century we may have a climate almost as different from today's as today's is from the peak of the last major glaciation." Mass migration, which society has used in the past to adjust to climate change, is no longer feasible.

The greatest economic impact of changing climate would probably fall on agriculture. The northern countries, which burn the coal in the first place, would likely benefit from the warming trend. The developing countries would become more arid. It might therefore become essential to control carbon dioxide production by restricting the use of fossil fuel -- a most difficult international task.

Carbon dioxide increase cannot, therefore, be ignored until its effects become apparent. By that time it may be too late. What is needed is an urgent research program to learn more about patterns of climate change and how to predict them. Meanwhiled, energy policy-makers must assume the worst; any policy that relies heavily on the use of coal is simply too big a risk. In the words of the National Academy, "This earth is the only planet we have on which to live" and, though human society has not yet destroyed its ability to support us, "we may just have been lucky . . . There is no guarantee that we will not get into trouble in ways that we have not discovered or even imagined."