The ozone layer that has shielded the Earth from damaging ultraviolet radiation since life began is diminishing. This is caused by the use we have made, over the past 60 years, of the ozone layer depleting substances, particularly CFCs and halons. Even if all such substances were banned tomorrow, we would still be committed to further ozone destruction throughout the next century because of the long-lived chemicals already released into the atmosphere. In fact, on the basis of phase-out dates laid down in the Montreal Protocol, it will take until about 2130 for these man-made compounds to disappear completely from the atmosphere.