Washington, Oct 25 (IANS): There is some good news on the ozone front - the average area covered by ozone hole over the Antarctic this year is the second smallest in the last 20 years.

The ozone hole reached its maximum size Sep 22, covering 8.2 million square miles (21.2 million sq km), or the area of the US, Canada and Mexico combined, according to data from NASA and National Oceanic and Atmospheric Administration (NOAA) satellites.

The average size of the 2012 ozone hole was 6.9 million sq miles (17.9 million square km). The Sep 6, 2000 ozone hole was the largest on record at 11.5 million square miles (29.9 million sq km).

Ozone layer acts as Earth's natural shield against ultraviolet radiation, which can cause skin cancer. The ozone hole phenomenon began making a yearly appearance in the early 1980s.

"The ozone hole mainly is caused by chlorine from human-produced chemicals, and these chlorine levels are still sizable in the Antarctic stratosphere," said atmospheric scientist Paul Newman of NASA's Goddard Space Flight Centre in Greenbelt, according to a NASA statement.

"Natural fluctuations in weather patterns resulted in warmer stratospheric temperatures this year. These temperatures led to a smaller ozone hole," added Newman.

The Antarctic ozone layer likely will not return to its early 1980s state until about 2065, Newman said. The lengthy recovery is because of the long lifetimes of ozone-depleting substances in the atmosphere.

Overall atmospheric ozone no longer is declining as concentrations of ozone-depleting substances decrease. The decrease is the result of an international agreement regulating the production of certain chemicals.