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When it does, the area of greatest ozone depletion and greatest danger will most likely be north of 50 degrees north latitude, a line that nearly coincides with the U.S.-Canada border and also takes in all the British Isles, Scandinavia, the Netherlands and much of Belgium, Germany and Russia. Regions farther to the south could be affected too, albeit not so severely. Life in the far north could come to resemble that in Australia, with ozone alerts and stern warnings to wear sunglasses and sunscreen.
Some scientists are equally concerned about the smaller but worsening ozone loss at mid-latitudes. The mechanism behind polar ozone holes was not predicted before its discovery. Could there be an undiscovered reason for ozone to vanish over temperate zones as well? Maybe so. On Jan. 12 the ER-2 swooped south instead of north. Says Anderson: "We discovered to our shock that there was ClO all the way down to the Caribbean." It was a very thin layer with concentrations of only 0.1 part per billion -- but this was much higher than anyone had predicted.
No one is sure just how such concentrations of the chemical got there or whether it is destroying ozone. It may be that some of the ClO-rich air from the polar vortex has split off and headed south on its own -- a phenomenon that has been observed in the past. And while ozone depletion has not been directly observed, the chemistry over the Caribbean appears to be right. There is ClO; there are plenty of dust particles from Pinatubo; there is sunlight. NASA's Kurylo thinks significant ozone loss is in fact happening in the tropics. Says Harvard's Anderson: "This is cause for extreme concern. It is the mechanism we most fear."
What also frightens scientists is the fact that CFCs remain in the atmosphere for decades after they are emitted. In their original research, Rowland and Molina estimated that CFCs can last 100 years or more. Even if CFC production stopped today, researchers believe that stratospheric levels of chlorine would continue to rise, peaking during the first decade of the next century and not returning to anything like natural levels for at least a century.
The ozone story is a tragic saga of doubt and delay. Rowland recalls that for several months after his original ozone paper was published in 1974, "the reaction was zilch." It was not until 1978 that the U.S., but not most other countries, banned the use of CFCs in hair sprays and other aerosols. Not until the Antarctic ozone hole was confirmed in 1985 did nations get serious about curbing all uses of CFCs. By now as many as 20 million tons of these potent chemicals have been pumped into the atmosphere.
World leaders should remember ozone when they think about other threats to the planet. If they always wait until there is indisputable evidence that serious damage is occurring, it may be much too late to halt the damage. Consider the widespread scientific predictions of global warming from the greenhouse effect. No one knows for sure that anything terrible will happen. ! But humanity has boosted the amount of carbon dioxide in the atmosphere by at least 25%. It is reckless to subject nature to such giant experiments when the outcome is unknown and the possible consequences are too frightening to contemplate.