A quick question for people who discount the idea that global warming could be caused, in part, by human activities on the basis that we can’t possibly impact the climate as much as natural events and cycles affect it.

Do you also discount the well-documented depletion of the ozone layer by interaction with CFCs and similar chemicals? That seems to be a major environmental impact, and one that clearly has an anthropogenic component.

Nearly two decades after we cut back on CFC use, it looks like the ozone layer is finally starting to recover—or at least it’s stopped shrinking. Of course, it’ll take time. The whole reason we started using CFCs is that they didn’t seem to react with anything, so they’ll stay in the atmosphere for decades. UCI’s Sherwood Roland (who won a Nobel Prize for research on this topic) is quoted as saying, “This problem was a long time in the making, and because of the persistence of these chlorine compounds, there is no short-term fix.”