An international team of researchers led by Prof. Susan Solomon of the Massachusetts Institute of Technology (MIT) has identified the first ‘fingerprints of healing’ of the Antarctic ozone layer.
A simulation of the Antarctic ozone hole, made from data taken on October 22, 2015. Image credit: NASA’s Goddard Space Flight Center.
Prof. Solomon and her colleagues from the National Center for Atmospheric Research in Boulder, Colorado, MIT, and the University of Leeds, UK, tracked the yearly opening of the Antarctic ozone hole in the month of September, from 2000 to 2015.
The scientists analyzed ozone measurements taken from weather balloons and satellites, as well as satellite measurements of sulfur dioxide emitted by volcanoes, which can also enhance ozone depletion.
And, they tracked meteorological changes, such as temperature and wind, which can shift the ozone hole back and forth.
The researchers then compared their yearly ozone measurements with model simulations that predict ozone levels based on the amount of atmospheric chlorine originating from chlorofluorocarbons (CFCs).
They found that the ozone hole has declined compared to its peak size in 2000, shrinking by more than 1.7 million square miles (more than 4 million square km) by 2015.
They further found that this decline matched the model’s predictions, and that more than half the shrinkage was due solely to the reduction in atmospheric chlorine.
The team attributes this improvement to the 1987 Montreal Protocol, which heralded a ban the use of CFCs — then widely used in cooling appliances and aerosol cans.
“We can now be confident that the things we’ve done have put the planet on a path to heal,” Prof. Solomon said.
“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 Montreal Protocol is a true success story that provided a solution to a global environmental issue,” added co-author Dr. Anja Schmidt, from the University of Leeds.
The team’s research had shed new light on the part played by recent volcanic eruptions – such as at Calbuco in Chile in 2015 – in Antarctic ozone depletion.
“Despite the ozone layer recovering, there was a very large ozone hole in 2015,” Dr. Schmidt said.
“We were able to show that some recent, rather small volcanic eruptions slightly delayed the recovery of the ozone layer.”
“That is because such eruptions are a sporadic source of tiny airborne particles that provide the necessary chemical conditions for the chlorine from CFCs introduced to the atmosphere to react efficiently with ozone in the atmosphere above Antarctica. Thus, volcanic injections of particles cause greater than usual ozone depletion.”
The team’s results are published today in the journal Science.
_____
Susan Solomon et al. Emergence of healing in the Antarctic ozone layer. Science, published online June 30, 2016; doi: 10.1126/science.aae0061
