MercoPress. South Atlantic News Agency

In 50 years ozone layer could be back to normal

The hole in the ozone layer of the earth's atmosphere is recovering and could significantly contract in the next 50 to 60 years according to scientists from the United States National Oceanic and Atmospheric Administration, NOAA.

The ozone layer blocks the sun's ultra-violet rays, exposure to which is harmful to humans, animals and plants.

The announcement was made Tuesday in Washington by a group of scientists on the twentieth anniversary of the discovery of the ozone layer hole over Antarctica in August 1986.

Their efforts helped determine the chemical basis for the ozone loss and formed the scientific basis for the resulting international treaty phasing out the production of chlorofluorocarbons, or CFCs, which has led to a decline in ozone-depleting gases.

"I'm very optimistic that we will have a normal ozone layer sometime, not in my lifetime, but perhaps in yours" said Dr David Hofman, director of Global Monitoring for NOAA.

"The discovery of ozone depletion and the response of the scientific community constitute nothing less than a scientific success story" said Susan Solomon, winner of the 2004 Blue Planet Award and the 1999 National Medal of Science for her work. However "there's a lot more to be done from a scientific perspective in terms of what I would call accountability".

The work by the team provided the scientific basis for the Montreal Protocol on Substances That Deplete the Ozone Layer, an international treaty begun in the late 1980s designed to protect the ozone layer by phasing out the production of ozone-depleting substances.

NOAA said the improvement in the ozone layer was caused largely by the phasing out of CFCs (chlorofluorocarbons) from products such as aerosol sprays and refrigerators. The ozone layer is a thin, invisible layer of the Earth's atmosphere about 15 miles thick. A British Antarctic Team first looked at results that showed a decline in stratospheric ozone over Antarctica in 1985, and doubted their findings. After rechecking their data and their instruments, they determined that there was a hole in the ozone.

Theories about the cause included solar activity that affected the magnetic field, atmospheric motions and chemical reactions involving chlorofluorocarbons (CFCs), which had been used since the 1930s as refrigerants and propellants, such as aerosol sprays.

The work conducted by the Antarctic team in the 1986 field study was the first to show that a chemical reaction triggered by the CFCs was indeed the cause. Scientific papers have been published recently showing early signs of a leveling off of ozone loss, linked to the success of international agreements to control CFC emissions worldwide. Part of NOAA's global environmental observing mission is to continue monitoring ozone and ozone-depleting gases. NOAA has a new Ozone Depleting Gas Index, a number based on NOAA's measurements of all the ozone-depleting gases that indicates how far along we are towards pre-ozone hole conditions.

Hofmann said the ODGI indicates that the ozone-depleting potential of the gases has already declined, in agreement with the early signs of leveling off of ozone loss and the success of the Montreal Protocol.