What would have happened without the Montreal Protocol?
One measure of success of the Montreal Protocol and its subsequent Amendments and Adjustments, according to the Assessment, is the forecast of “the world that was avoided” by the Protocol: • The abundance of ozone-depleting gases in 2050, the approximate time at which the ozone layer is now projected to recover to pre-1980 levels, would be at least 17 ppb of equivalent effective chlorine (this is based on the conservative assumption of a 3% per annual growth in ozone-depleting gases) which is about five times larger than today’s value; • Ozone depletion would be at least 50% at mid-latitudes in the Northern Hemisphere and 70% at mid-latitudes in the Southern Hemisphere, about 10 times larger than today; and • Surface UV-B radiation would at least double at mid-latitudes in the Northern Hemisphere and quadruple at mid-latitudes in the Southern Hemisphere compared to an unperturbed atmosphere. This compares to the current increases of 5% and 8% in the Northern and Southern hemispheres, r
