GENEVA, Oct. 3 (Xinhua) -- The hole in the ozone layer above Antarctica this year has surpassed the record size registered in 2000, the World Meteorological Organization (WMO) said on Tuesday.

The Geneva-based agency said that data from the U.S. National Aeronautics and Space Administration (NASA) showed that the ozone hole had grown to 29.5 million square kilometers.

"This is the most serious on record," said Mark Oliver, spokesman for the WMO.

"It has been caused by a particularly cold stratospheric winter, between 10 and 40 km above sea level," he told journalists.

The new size of the ozone hole was recorded by NASA on Sept. 25,he said. The previous record of 29.4 million square kilometers was set in September 2000.

Ozone, a molecule of oxygen, filters out dangerous ultraviolet rays from the Sun that damage vegetation and can cause skin cancer and cataracts.

Scientists say the layer has been badly damaged by man-made chemicals, especially by chlorine and chlorofluorocarbons (CFCs), which are used as aerosol gases and refrigerants.

The chemical reaction that thins ozone reaches its peak with colder high altitude temperatures in the southern hemisphere winter, normally in late August to October.

CFCs and other ozone enemies were controlled by an international treaty signed 19 years ago.

But large ozone holes are expected to persist for the next couple of decades because of the amount of pollutants already stored in the atmosphere. Enditem