Our of curiosity, can someone tell us how big the ozone hole was in 1900? 1800? It wasn't discovered until the late 1970's. It's made some fluctuations since them but is there evidence that it's actually larger than it was 100 or 200 years ago?
You have essentially answered your own question. No one knows. We could assume that during past times of unusually high volcanic activity, it may have been larger but there is no way to know for sure.
The key assumption, if he is correct, is that we have spent billions (and are proposing to spend hundreds of billions more) dollars to reduce CO2 emissions which may do little or nothing to ameliorate climate change.
