An international agreement to limit ozone-depleting chemicals appears to be helping the ozone layer to recover, but it is unlikely to be restored to pre-1980 levels, a new study suggests.
Ozone in the Earth's stratosphere filters out ultraviolet light from the sun, and helps to protect DNA from damage.
Ozone depletion is linked to a higher risk of skin cancer and cataracts in humans, and harmful effects on plants.
Since 1987, 180 nations have ratified the Montreal Protocol banning ozone-depleting chemicals such as chlorofluorocarbons used in aerosol sprays and in refrigeration products.
Researchers in the U.S. and Denmark analyzed data from satellites and ground stations, as well as modelling studies, to review trends in ozone level measurements.
The ozone layer showed signs of stabilizing or increasing slightly in the past 10 years but it's unlikely to recover to a level observed before 1980, because the atmosphere itself is changing, they conclude in Thursday's issue of the journal Nature.
The poles show the worst depletion, and the mid latitudes of North America, South America and Europe are next, the researchers said.
Recent studies on ozone recovery failed to take into account the effects of volcanic eruptions and solar storms, said study authors Betsy Weatherhead of the University of Colorado in Boulder and Signe Bech Andersen of the Danish Meteorological Institute in Copenhagen.
For example, the eruption of Mount Pinatubo in the Philippines in 1991 released sulphates that destroy ozone.
Observations this decade may help scientists to better understand the link between ozone and temperature, the pair said. [CBC.ca]
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