Ozone hole closing up

A new study using

and

(NOAA) data has found consistent evidence that Earth's ozone layer is on the mend.

A team led by Eun-Su Yang of the Georgia Institute of Technology, Atlanta, analysed 25 years of independent ozone observations at different altitudes in Earth's stratosphere, which lies between six and 31 miles above the surface. The observations were gathered from balloons, ground-based instruments, NASA and NOAA satellites.

The stratosphere is Earth's second lowest atmospheric layer. It contains approximately 90 percent of all atmospheric ozone. The researchers concluded the Earth's protective ozone layer outside of the polar regions stopped thinning around 1997. Ozone in these areas declined steadily from 1979 to 1997.

The abundance of human-produced ozone-destroying gases such as chlorofluorocarbons peaked at about the same time; 1993 in the lowest layer of the atmosphere, 1997 in the stratosphere. Such substances were phased out after the 1987 international Montreal Protocol was enacted.