The ozone hole over Antarctica was a threat that required and received a rapid response. It did not, however, totally go away and has been fluctuating. The first time the world responded required a large concerted effort and the threat eventually diminished. Recently, the hole expanded again. A particular chemical was suspected, HCFC-133a, but the specific cause and response weren’t apparent. And then, the concentration dramatically decreased and the threat diminished again; but this time the reduction was rapid. The rapidity of the corrections suggests that it is possible that two or three factories had inefficient processes that leaked the chemical into the atmosphere, and that they fixed those processes independently. That’s the good news. The bad news is that the event points out how sensitive the atmosphere is, even to individual sources.