The hole in the ozone layer, prominently displayed in Al Gore’s 2006 movie, an inconvenient truth has been oscillating in size and generally shrinking since 1996. It’s currently reached its second lowest size on record.

South pole ozone hole (blue circle in photo), shrinks to its 2nd smallest size on record. Note outline of antarctica plus end of south america and africa. Photo Credit: BIRA/IASB

The reason for the oscillation is unknown. The ozone hole is small this year, was large for the last few years, and was slightly smaller in 2002. My guess is that it will be big again in 2013. Ozone is an alternate form of oxygen containing three oxygen atoms instead of the usual two. It is an unstable compound formed by ions in the upper atmosphere acting on regular oxygen. Though the ozone concentration in the atmosphere is low, ozone is important because it helps shield people from UV radiation — radiation that could otherwise cause cancer (it also has some positive effects on bones, etc.).

An atmospheric model of ozone chemistry implicated chlorofluorocarbons (freons) as a cause of observed ozone depletion. In the 1980s, this led to countries restricting the use of freon refrigerants. Perhaps these laws are related to the shrinkage of the ozone hole, perhaps not. There has been no net decrease in the amount of chlorofluorocarbons in the atmosphere, and the models that led to banning them did not predicted the ozone oscillations we now see are common — a fault also found with models of global warming and of stock market behavior. Our best computer models do not do well with oscillatory behaviors. As Alan Greenspan quipped, our best models successfully predicted eight of the last five recessions. Whatever the cause, the good news is that the ozone hole has closed, at least temporarily. Here’s why the sky is blue, and some thoughts on sunlight, radiation and health.

by Dr. Robert E. Buxbaum, dedicated to bringing good news to the perpetually glum.