Changes in climate are expected to have an increasing influence on stratospheric ozone in the coming decades, the report says. "These changes derive principally from the emissions of long-lived greenhouse gases, mainly carbon dioxide, associated with human activities."

An important remaining scientific challenge is to project future ozone abundance based on an understanding of the complex linkages between ozone and climate change.

UN Secretary-General Ban Ki-moon today called the Montreal Protocol "an excellent example" of setting a broad framework, clear targets and a gradual approach to implementation as governments gain confidence and build on initial steps, setting more ambitious goals.

"When the Montreal Protocol was signed in 1987, governments did not originally envision the phase-out of any ozone-depleting substance," said Ban. "Yet, as a result of strong national and global compliance, parties to the Montreal Protocol have cut production and consumption of these harmful chemicals by more than 98 percent."

Michel Jarraud, secretary-general of the World Meteorological Organization, WMO, said, "The ozone-hole issue demonstrates the importance of long-term atmospheric monitoring and research, without which ozone destruction would have continued unabated and might not have been detected until more serious damage was evident."

The Antarctic ozone hole was discovered in 1985 by British scientists Joe Farman, Brian Gardiner, and Jonathan Shanklin of the British Antarctic Survey.

Shanklin said, "This discovery was a crucial reminder of the importance in investing in long-term monitoring, but perhaps the most startling lesson from the ozone hole is just how quickly our planet can change."

In Antarctica today, high levels of ultraviolet radiation continue to be seen when the springtime ozone hole is large, the report finds.

There is a complex trade-off between banning ozone depleters and dealing with the harm caused by their replacements.

Many ozone depleting chemicals, such as CFCs, chlorofluorocarbons, once present in products such as refrigerators and spray cans, have been phased out.

But demand for replacement substances called HCFCs, hydrochlorofluorocarbons, and HFCs, hydrofluorocarbons, has increased. Many of these are powerful greenhouse gases.

The report projects that total emissions of HCFCs will begin to decline in the coming decade due to measures agreed under the Montreal Protocol in 2007. But they are currently increasing faster than four years ago.

The most abundant one, HCFC-22, increased more than 50 percent faster in 2007-2008 than it did in 2003-2004.

Abundances and emissions of HFCs currently are increasing at about eight percent per year, according to the report.

HFC-23 is a byproduct of HCFC-22 production. Although it has no impact on the ozone layer it is more than 14,000 times more powerful as a climate-warming greenhouse gas than carbon dioxide, the most abundant greenhouse gas.