Shore up the ozone layer

LITTLE excuse remains for nations to continue using gases that are destroying Earth's chemical sunscreen. Ratification of a treaty restricting the use of such chemicals, which 31 nations signed last September in Montreal, should become a priority for those countries that haven't yet put their official stamp on it.

The National Aeronautics and Space Administration sponsored a global study that documents a 15-year decline in the ozone layer, a sheath of gas surrounding Earth that cuts the amount of ultraviolet light reaching the planet's surface. The decline is not confined to a highly publicized ``hole'' over the Antarctic. It covers the highly industrialized and highly populous Northern Hemisphere.

The culprits are chlorofluorocarbons (CFCs), used for refrigeration and in certain industrial processes, and halon, used in fire extinguishers.

So far, the United States and Mexico are the only countries that have ratified the Montreal pact, which freezes and then rolls back production of the chemicals. By January a total of 11 nations representing two-thirds of global production of the chemicals in question must ratify the treaty if it is to take effect.

After the treaty has been ratified, efforts should be made to tighten its restrictions. For example, the pact lets developing countries exceed caps on CFC use if the pact's limits threaten their economic development. The net effect, even if unintended, is once again to foist off on developing countries the products and processes the industrialized nations see as environmental threats at home.

Chemical companies are trying to find substitutes for CFCs and their ilk, though some of the new products appear to be more expensive. Assuming that new compounds show no harmful side effects, their use should be required as part of industrial development programs. If substitutes cost more, then boost aid enough to compensate.

Researchers are likely to pick nits with this and other ozone studies. Highlighting uncertainties is a matter of scientific honesty. But the evidence mounting against CFCs is too strong to be ignored.