Ozone hole stabilizes

A recent image of the ozone hole.

WASHINGTON (CNN) -- A hole in the Earth's protective ozone layer is about the same size as in the past three years, according to scientists at the National Oceanic and Atmospheric Administration, who predict it will hold steady in the near future.

Satellite data show the hole over Antarctica, which allows more harmful solar radiation to reach the Earth, peaked this year at about 10 million square miles (26 million square km), roughly the size of North America.

The hole has remained roughly the same in both area and thickness over the past several years, NOAA said Tuesday in a news release.

The hole generally reaches its maximum size in mid-October.

In the near future, NOAA said, the ozone hole "will likely remain similar" to its size in recent years. In the long term, over a period of 30 to 50 years, the hole is expected to shrink as certain chemicals in the atmosphere decline, NOAA said.

The ozone layer is eaten away when some man-made chemicals, notably chlorofluorocarbons (CFCs), bond with ozone molecules, destroying them in the process. CFCs were invented in the 1920s and served as the primary source of cooling for most refrigerators and air conditioners until they were banned in 1987.

CFCs were banned internationally by the 1987 Montreal Protocol, a treaty often praised as a model for global environmental cooperation. The ban is considered to be largely effective, although several high-profile arrests of CFC smugglers have demonstrated an illicit market still exists for CFCs, which are much less expensive than the substitute refrigerants now in widespread use.

The regulations are a main reason for the decline in ozone-depleting chemicals.

Nobel Prize-winning chemist Sherwood Rowland and other researchers predicted last year the ozone hole would continue to grow through the first decade of the 21st century, followed by four or five decades of "healing." They said if the ban on CFCs holds, the ozone hole could close up by the end of the 21st century.

Considered a major air pollutant at ground level, ozone in the upper atmosphere absorbs ultraviolet radiation from the sun. When the ozone layer is thinned or absent, that harmful radiation reaches Earth in much greater quantity, posing a substantial skin cancer risk to humans and potentially affecting vegetation and oceanic plankton -- the basis of life in the rich waters surrounding Antarctica.

In recent years, a documented rise in skin cancers in Australia and southern Chile and Argentina is believed to be linked to the ozone problem.