There's bad and good news from the ozone front.

The bad news first: NASA scientists say that the amount of ultraviolet (UV) radiation reaching the Earth's surface has increased dramatically over the past 30 years. The reason for the increase is a continuing decrease in the protective stratospheric ozone layer, a colorless gas located about 10 to 20 miles above the Earth. The ozone absorbs much of the ultraviolet energy from the sun that could cause skin cancer and harm living things, including plants, if it reaches the ground or oceans.

The good news: The amount of the UV increase seems to have stabilized since the mid-1990s.

This finding backs up other research that shows UV levels are stabilizing after countries began signing an international treaty in 1987 that limited the emissions of ozone-depleting gases such as chlorofluorocarbons (CFCs).

In 1987, the Montreal Protocol treaty and amendments since then have greatly reduced the amounts of ozone-destroying substances (not only CFCs) being released into the air.

"Overall, we're still not where we'd like to be with ozone, but we're on the right track," said NASA scientist Jay Herman. "We do still see an increase in UV on a 30-year timescale, but it's moderate, it could have been worse, and it appears to have leveled off."

Geographically, most of the UV increase has occurred in the mid-and-high latitudes, with little or no increase observed in tropical regions.

The results were published last month in the Journal of Geophysical Research.

By Doyle Rice