The "hole" in the ozone layer over Antarctica has increased since last year, but is not as large as it was in 2006, according to the European Space Agency (ESA).

Ozone is a protective atmospheric layer found in about 25 kilometres altitude that acts as a sunlight filter shielding life on Earth from harmful ultraviolet rays, which can increase the risk of skin cancer and cataracts and harm marine life.

The ozone "hole" is a thinning in the ozone layer over Antarctica and varies every year depending on weather conditions. The ESA says this year that area over the South Pole reached about 27 million square kilometres, more than the 25 million square kilometres recorded in 2007.

However it is not as big as 2006's record ozone hole of 29 million square kilometres in 2006, which is about the size of the North American continent.

The ESA says the depletion of ozone is caused by extreme cold temperatures at high altitude and the presence of ozone-destructing gases in the atmosphere such as chlorine and bromine, originating from man-made products like chlorofluorocarbons (CFCs), which were phased out under the 1987 Montreal Protocol but continue to linger in the atmosphere.

Scientists say that since the size and precise time of the ozone hole is dependent on the year-to-year variability in temperature and atmospheric dynamics, the detection of signs of ozone recovery is difficult.

© NewsRoom 2008