Newly released images from NASA show that the ozone hole currently developing over Antarctica has grown in size to around 9 million square miles (21 million square kilometers), and may continue to expand.
Scientists expect the hole to peak in the next few weeks, possibly making 1999 the worst year ever recorded for the destruction of the ozone layer.
In September 1998, the hole measured 10.5 million square miles (27.3 million square kilometers).
The ozone hole above the Antarctic develops each year between late August and early October. Ozone protects Earth's inhabitants by absorbing dangerous ultraviolet radiation from the sun.
A more urgent sign of the ozone's destruction this year, NASA says, is the development of a secondary hole of an unusually large size over the frozen continent.
The images were taken by the Total Ozone Mapping Spectrometer (TOMS) instrument aboard NASA's Earth Probe satellite.
In the image, lower concentrations of ozone are shown in purple, with higher ones in yellow and red.
Scientists from NASA and the National Oceanic and Atmospheric Administration (NOAA) have been measuring the ozone layer, which exists in the Earth's stratosphere 6-to-18 miles high, since the early 1970s.
But a hole in the layer wasn't spotted until the 1980s.
And while scientists expect that efforts to reduce the emission of ozone-destroying Chlorofluourocarbons (CFCs) will soon limit the growth of the ozone hole, cold winters in recent years might account for the particularly destructive period, NASA says.
In cold weather, ice crystals form and serve as a kind of perch for the chlorine which rises through the atmosphere as part of the CFCs, which are emitted from some aerosol containers and refrigerants.
Chlorine serves as a catalyst for a process that destroys ozone, turning it into breathable oxygen. This allows dangerous rays to pass through to the Earth's surface relatively uninhibited.
Those rays have been blamed for an increase in the incidence of skin cancer.
The cold weather also assists ozone destruction by removing a natural defense process.
"Nitrogen compounds up there would interfere with the chlorine, but it's so cold they freeze out on these ice crystals," says Richard McPeters, principal investigator for the Earth probe TOMS. "So there's nothing there but raw chlorine."
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