Ozone hole on the mend – Expert reaction

After persisting for decades, the hole in the ozone layer over Antarctica has begun to ‘heal’, exhibiting an ozone increase.

A simulation of the Antarctic ozone hole, made from data taken on October 22, 2015.New research from US and UK researchers, published in Science, reports that international efforts to control ozone-depleting chemicals are paying off. Regular and consistent increases in ozone have been detected using several different methods, giving a clear signal that the ozone hole is healing.

The authors used “fingerprints” of the ozone changes with season and altitude to attribute the ozone’s recovery to the continuing decline of atmospheric chlorine originating from chlorofluorocarbons (CFCs). These chemical compounds were once emitted by dry cleaning processes, old refrigerators, and aerosols such as hairspray. In 1987, virtually every country in the world, including New Zealand,  signed on to the Montreal Protocol in a concerted effort to ban the use of CFCs and repair the ozone hole.

“We can now be confident that the things we’ve done have put the planet on a path to heal,” says lead author Susan Solomon, the Ellen Swallow Richards Professor of Atmospheric Chemistry and Climate Science at MIT. “Which is pretty good for us, isn’t it? Aren’t we amazing humans, that we did something that created a situation that 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.”

Read more about the research on Scimex.org.

The Science Media Centre collected the following commentary from New Zealand experts:

Dr Joseph Lane, Senior Lecturer in Physical and Theoretical Chemistry, University of Waikato, comments:

“The reduction in the size of the ozone hole is an exciting result that will provide real benefit to New Zealanders, particularly those who spend significant time outdoors or who are prone to developing melanoma.

“The ozone layer is expected to continue to slowly recover as a direct result of the Montreal Protocol, which globally restricts the use of ozone depleting substances such as chlorofluorocarbons (CFCs). However there remains some uncertainty in the rate of recovery, with atmospheric emissions of nitrous oxide (an unregulated ozone depleting substance) continuing to climb.”

Dr Olaf Morgenstern, Principal Scientist – Atmosphere and Climate, NIWA, comments:

“Unlike the onset of the ozone hole (whose discovery in 1985 came as a shock) the beginning of its demise does not come as a surprise. It is a consequence of the successful implementation of the Montreal Protocol which regulates the phase-out of ozone-depleting substances.

“For a few years, scientists have been arguing whether ozone recovery is now evident or not (one or two authors had used questionable methods to infer this), but the longer the Montreal Protocol is in place, the easier ozone recovery will be to identify and the more unambiguous the finding will be. At the time of the 2014 Scientific Assessment of Ozone Depletion (which summarizes the state of ozone science every four years) they erred on the side of caution and in the Assessment for Decision Makers only wrote that the ozone hole continues to occur every spring.

“This new research is consistent with that. It is also consistent with model projections which indicate a gradual healing of the ozone hole and its disappearance in the second half of this century. The authors just find that this process is now advanced enough for positive trends in Antarctic total-column ozone to become apparent, when previously such trends had been masked by natural variability. Ozone healing would have started in ~2000 when the stratospheric chlorine loading started to decrease.”

From our colleagues at the AusSMC:

Dr Roger Dargaville is Deputy Director of the Melbourne Energy Institute at the University of Melbourne, comments:

“Much respected scientist Susan Solomon and colleagues from the USA and UK have published analysis showing that the Antarctic ozone hole is beginning to recover. This news may come as a surprise to many, as the general lack of news coverage about this topic may have led some people to think the problem was solved. But, the depletion of ozone over Antarctica in the spring remains a serious issue. The chemicals that drive ozone depletion have been decreasing in concentration for several years, but they have long lifetimes in the atmosphere and it will be decades yet before the ozone layer will have entirely recovered. The analysis published today strongly suggests that recovery process is now observable.

There is a common misconception that the ozone hole extends over Australia, and that ozone depletion is the reason why we need to be particularly vigilant with sunscreen etc in the Australian summer. Skin cancer is of serious concern because of the natural high concentrations of UV received in our part of the world. But, had the Montreal Protocol not been signed in 1987, beginning the process to phase out CFCs, the ozone hole could well have expanded over Australia which would have had disastrous consequences for humans, animals and plants.”