How Do You Patch a Hole in the Sky That Could Be as Big as Alaska?

Think for a moment about the world's 1 billion refrigerators and its hundreds of millions of air conditioners. Picture mountains of foam insulation, seat cushions, furniture stuffing and carpet padding. Imagine streams of cleaning fluids, rivers of industrial solvents, wafting clouds of aerosol spray.

Ridding the planet of the millions of tons of ozone-depleting chemicals contained in that vision is not just a big job; it may be the biggest job the nations of the world have ever taken on. In the 60 years since Du Pont began marketing the miracle refrigerant it called Freon, chlorofluorocarbons have worked their way deep...