Record size: The ozone layer hole is situated over the Antarctic.
Last Update: Wednesday, October 4, 2006. 7:04am (AEST)

Ozone layer hole reaches record size

The hole in the ozone layer above Antarctica has beaten the record size logged six years ago, the United Nations' weather agency says.

The World Meteorological Organisation (WMO) says data from the US National Aeronautics and Space Administration (NASA) shows the hole in the atmospheric layer that guards the world against dangerous ultraviolet light has grown to 29.5 million square kilometres.

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

"It has been caused by a particularly cold stratospheric winter."

Mr Oliver says the hole was recorded by NASA on September 25 and just beats the previous record of 29.4 million square kilometres, which was set in September 2000.

There is growing body of evidence that 2006 will be a bad year for the Antarctic ozone layer, with scientists agreeing that the hole has reached record proportions.

The hole measured by NASA is slightly bigger than the 28 million square kilometres announced by the European Space Agency (ESA) on Monday.

However, the ESA also discovered other records: a loss of 40 million tonnes of ozone in October, exceeding the previous high of 39 million tonnes set in 2000.

Ozone loss is calculated by measuring the area and depth of the ozone hole in the stratosphere, about 25 kilometres above Earth's surface.

The ESA says the depth of the hole rivals a record set in 1990.

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.

- AFP