Even though human civilization is responsible for less than 1% of all chlorine in the atmosphere, it is responsible for 80% of all ozone-destroying chlorine. Why?
Some kinds of human-made molecules that contain chlorine can survive the trip up to the ozone layer, while most naturally produced chlorine-containing molecules cannot. Thus, although we produce few chlorine-containing molecules, many of them can reach the ozone layer, where ozone depletion can occur. As a result, most of the ozone-destroying molecules in the ozone layer are from human sources.