The southern winter is drawing to a close, and that means the annual destruction of the ozone layer in the upper atmosphere over the South Pole is peaking. NASA has posted a new image showing the ozone hole as satellite sensors found it late last week.

Scientists discovered 20 years ago that the release of man-made chlorofluorocarbons (CFCs) into the atmosphere was catalyzing the destruction of ozone molecules. And the losses were greatest at the South Pole, where they amounted to a "hole."

High-altitude ozone is critical to life on the surface of the planet because it absorbs ultraviolet radiation from the sun, protecting exposed tissues from possible genetic damage - damage that can cause cancers and other harm to life forms from ocean plankton to people.

Continued ozone damage was affecting the polar regions first, but would eventually erode the ozone layer everywhere, enough to pose increasing health threats in the temperate zones where most people - most life forms - live.

International treaties in 1987 led to the phase-out of CFCs in refrigerants and aerosol propellants, and their replacement by more environmentally friendly materials.

Scientists in the nearly 20 years since have been on the lookout for signs the global actions have had some beneficial effect. Happily, they now say the long-term decline in the ozone layer globally has at least halted, and the damage may be healed (or at least back to 1980 levels) in the coming decades - well within the lives of our children and grandchildren. Here's a NASA release on the subject, noting that the best explanation for the gains is the ban on CFCs.

It's great to hear that human societies can learn about and understand a global environmental threat, and take concerted action - even when the payoff may be years or decades away.