A few weeks back, we checked in on the ozone hole which appears annually over the Antarctic. The hole is the result of a reduction of ozone gas in the stratosphere 10 to 30 miles up. However, this year's ozone hole was anything but ordinary.

Typically, the ozone hole starts forming in August, reaches its greatest extent in September, and then disappears in October and November. This year, however, in late September, an infusion of higher-ozone air from farther north infiltrated the hole and actually caused it to split into two smaller pieces. Eventually, in early October, the ozone hole did reform into one blob, but overall its size and the extent of ozone depletion didn't come anywhere close to previous years.

Though highly unusual, this year's less severe ozone hole shouldn't be taken as a trend. The area of the ozone hole varies naturally from year to year depending on how cold it is over the Antarctic. And according to atmospheric chemists, there's still enough ozone-destroying chemicals in the air for the ozone hole to make a yearly appearance for many more decades to come.