A study published in Science claims to offer the first compelling evidence that the hole in the ozone layer above the Antarctic is shrinking. This study, conducted by US and UK scientists, contains data collected annually between September 2000 and September 2015, which demonstrates a decline of 4 million sq km in the size of the ozone hole during this period.
The study’s authors attribute the good news to the phasing out of Chlorofluorocarbon (CFC) chemicals since a global ban was introduced with the 1987 Montreal Protocol.
The study is also the first to highlight the role of volcanic activity in ozone depletion.
Ozone depletion and CFCs
Ozone is a gas which is present in the stratosphere, where it serves to protect humans, animals and plants on Earth by blocking harmful ultraviolet radiation coming from the Sun. For humans, exposure to UV radiation raises the risk of skin cancer and cataract damage.
Although depletion and production of ozone both occur naturally in the stratosphere, the level of ozone has been historically constant.
Yet in the mid 1980s British scientists discovered a dramatic thinning of the ozone layer above the Antarctic. Subsequently, in 1986, work by US researcher Susan Soloman called attention to the destructive effects on the ozone of the chlorine and bromine molecules in CFCs, which at the time were present in everything from aerosols to refrigerators and air conditioning units.
Ozone hole shrinkage
According to a BBC News article, the declining influence of CFCs has been reported by other studies prior to this latest research; however, this is the first time evidence has been put forward that the hole in the ozone layer is actually shrinking.
Between 2000 and 2015, Prof Solomon and her colleagues conducted detailed measurements of ozone in the stratosphere using weather balloons, satellites and model simulations. By so doing, they found that the hole above the Antarctic has shrunk by 4 million sq km over this period. Over half of this gain was due to the reduction of atmospheric chlorine.
For Dr Markus Rex from the Alfred Wegener Institute for Polar and Marine Research in Germany, “This is the first convincing evidence that the healing of the Antarctic ozone hole has now started.” He ascribes this achievement to the Montreal Protocol, and sees this latest finding as “a big step forward.”
Nevertheless as Professor Soloman made clear, “Even though we phased out the production of CFCs in all countries including India and China around the year 2000, there’s still a lot of chlorine left in the atmosphere.”
Given that this has a lifetime of between 50 to 100 years, recovery is expected to be slow. “We don’t expect to see a complete recovery until about 2050 or 2060,” said Professor Soloman.
Yet, seemingly contrary to the reports conclusions, the reading taken in October 2015 showed the largest ozone hole on record; findings which at first baffled the researchers.
The reason that thinning of the ozone layer occurred predominantly over the Antarctic is due to the extreme cold and ample light in this region. Conditions which helped to create Polar Stratospheric Clouds, in which CFCs linger and eat away at the ozone.
Prof Solomon explained that “”After an eruption, volcanic sulphur forms tiny particles and those are the seeds for Polar Stratospheric Clouds.”
“You get even more of these clouds when you have a recent major volcanic eruption and that leads to additional ozone loss.”
In fact this study has been hailed as “historically significant” by some in the field for being the first to draw a connection between volcanic activity and ozone loss.
At the same time, there have been doubts raised by some in the field that the shrinkage in the ozone hole can be attributed to the decreasing amount of chlorine in the stratosphere.
Nasa’s Dr Paul Newman, for example, said, “The data clearly show significant year to year variations that are much greater than the inferred trends shown in the paper.”
“If the paper included this past year, which had a much more significant ozone hole due to lower wave driven forcing, the overall trend would be less.”
Even so, the researchers behind the study clearly believe strongly in their findings. For them, international efforts to tackle the hole in the ozone should serve as a model for other global environmental problems.
“This was an era in which international co-operation went rather well on some issues. I was inspired by the way the developed and developing countries were able to work together on dealing with the ozone hole,” said Prof Solomon.
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