The massive hole in the ozone layer above the Antarctic is healing says a new study led by researchers at Massachusetts Institute of Technology and University of Leeds.
The Ozone Layer
In the past 60 years the rise in population and human behavioural patterns has contributed to the deterioration of the ozone layer.
The ozone layer surrounds the Earth’s stratosphere and is part of the upper atmosphere, where the ozone is the highest concentration. At the upper region, the ozone absorbs ultraviolet radiation which stops it from returning back to the ground. This is harmful and cause skin cancer.
A paper in Nature in 1985 by Joe Farman, Brian Gardiner and Jonathan Shanklin found that there was a yearly depletion of ozone above the Antarctic. NASA scientists later discovered that the whole of the Antarctic was affected.
Ozone Hole Shrinking
The new study indicates that first signs of healing of the ozone hole are already showing up with the average size of the ozone hole having shrunk by more than 1.7 million square miles since 2000.
Scientists have attributed to the recovery of the ozone to the 1987 Montreal Protocol, which heralded a ban the use of chlorofluorocarbons (CFCs) – then widely used in cooling appliances and aerosol cans. While the recovery is evident, it has varied from year to year, due in part to the effects of volcanic eruptions. The team says that there is no reason why the ozone hole should not close permanently by the middle of this century.
Professor Solomon said:
“We can now be confident that the things we’ve done have put the planet on a path to heal.”
“We decided collectively, as a world, ‘Let’s get rid of these molecules’. We got rid of them, and now we’re seeing the planet respond.”
The ozone hole begins growing each year when the sun returns to the South Polar cap from August, and reaches its peak in October – which has traditionally been the main focus for research.
Banning Toxic Chemicals
In 1987 nearly every country signed the Montreal protocol, banning toxic chemicals in an attempt to repair the damaged ozone hole. Chlorofluorocarbons used to be emitted from aerosols and dry cleaning processes.
There are finally indications that a gradual healing of the ozone hole is beginning to take place in places like the Antarctic. The ozone healing began to improve around 2000 when the amount of stratospheric chlorine loading started decreasing.
Chlorine Levels Decreasing
The researchers believed they would get a clearer picture of the effects of chlorine by looking earlier in the year in September, when cold winter temperatures still prevail and the ozone hole is opening up. The team showed that as chlorine levels have decreased, the rate at which the hole opens up in September has slowed down.
Researchers from the British Antarctic Survey discovered in the mid-1980s that the October total ozone was dropping. Scientists worldwide typically tracked ozone depletion using October measurements of Antarctic ozone. Measurements have shown that ozone depletion starts each year in late August, as Antarctica emerges from its dark winter, and the hole is fully formed by early October
The researchers focused on September because chlorine chemistry is firmly in control of the rate at which the hole forms at that time of year, so as chlorine has decreased, the rate of depletion has slowed down.
Tracking of Antarctic Ozone Hole
They tracked the yearly opening of the Antarctic ozone hole each September from 2000 to 2015, analysing ozone measurements taken from weather balloons and satellites, as well as satellite measurements of sulphur dioxide emitted by volcanoes, which can also enhance ozone depletion. They also tracked meteorological changes, such as temperature and wind, which can shift the ozone hole back and forth.
They then compared yearly September ozone measurements with computer simulations that predict ozone levels based on the amount of chlorine estimated to be present in the atmosphere from year to year.
The researchers found that the ozone hole has declined compared to its peak size in 2000. They also discovered that this decline matched the model’s predictions, and that more than half the shrinkage was due solely to the reduction in atmospheric chlorine and bromine.
Key Facts
- The new study indicates that first signs of healing of the ozone hole are already showing up with the average size of the ozone hole having shrunk by more than 1.7 million square miles since 2000.
- The researchers believed they would get a clearer picture of the effects of chlorine by looking earlier in the year in September, when cold winter temperatures still prevail and the ozone hole is opening up.
- The team says that there is no reason why the ozone hole should not close permanently by the middle of this century.
- Professor Solomon said: “We can now be confident that the things we’ve done have put the planet on a path to heal.”
- The researchers found that the ozone hole has declined compared to its peak size in 2000.
