Dear Liza

There's a hole in the bucket:

In early October 2006, the Antarctic stratosphere was the coldest it has been since 1979, and the ozone hole loomed bigger than ever, spanning an area larger than North America. What's going on?
...
Climate studies in the 1970s and 1980s provided the first evidence that CFCs—found in items like hair spray, refrigerants, pesticides, plastics, and fire retardants—work their way into the stratosphere and unleash the chlorine atoms that initiate this destructive chain reaction. The Montreal Protocol and subsequent amendments have made a major dent in the problem by banning the use of most CFCs. "I think it's safe to say we're on the threshold of recovery," says Michelle Santee, an atmospheric scientist at NASA's Jet Propulsion Laboratory. But unlike pollutants that break down quickly, such as the sulfur compounds that cause acid rain, atmospheric chlorine can persist for more than 50 years. That helps explain why the ozone layer is still under attack, even though the amount of airborne chlorine is decreasing.

Still, why was this year's hole so huge? One possibility is that 2006 was simply colder than other years. Another possibility is that global warming could be contributing to the cold snap. Greenhouse gases, like carbon dioxide and methane, trap heat down near the surface. The result: colder temperatures in the stratosphere.

But see, the Earth is a balanced system so there's no way human activity could unbalance it...

ntodd