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EXPERT REACTION: The start of healing for the Antarctic ozone hole?

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After persisting for decades, the hole in the ozone over the Antarctic has begun to “heal,” exhibiting an ozone increase, suggests a new study by US and UK researchers. The results indicate that an historic agreement signed nearly three decades prior is having positive returns, not only in terms of slowing the rate of ozone depletion in Earth’s second major atmospheric layer (the stratosphere) but also in terms of creating an identifiable ozone increase.

Journal/conference: Science

Organisation/s: Massachusetts Institute of Technology, USA

Media release

The Start of “Healing” for the Antarctic Ozone Hole?

After persisting for decades, the hole in the ozone over the Antarctic has begun to “heal,” exhibiting an ozone increase, a new study reports. The results suggest that an historic agreement signed nearly three decades prior is having positive returns, not only in terms of slowing the rate of ozone depletion in Earth’s second major atmospheric layer (the stratosphere) but also in terms of creating an identifiable ozone increase. The Montreal Protocol on Substances that Deplete the Ozone Layer, which went into effect in 1989, is an international treaty designed to protect the ozone layer by phasing out the production of numerous substances responsible for ozone depletion. Understanding the degree to which the ozone is healing in response to this agreement and related efforts has remained of broad public, policy and scientific interest. Though analyses to date show some early signs of stratospheric ozone recovery since the agreement’s signing , these signs are largely in terms of a reduced rate of ozone decline and leveling off of ozone depletion; less has been documented about ozone increase in the polar regions. What’s more, in October of 2015 the Antarctic ozone hole reached a record size, providing a conflicting result. Here, to further examine polar ozone trends since 2000 in response to both controls of ozone-depleting substances and other variables, Susan Solomon and colleagues used a combination of direct ozone measurements and model calculations. They identified several consistent signals of “healing” in the Antarctic ozone layer, particularly in the month of September, when they found regular, seasonal increases in ozone column amounts. The researchers also evaluated changes in ozone health caused by natural factors including volcanic eruptions; since about 2005, they say, these eruptions have delayed healing and made a large contribution to the interannual variability in o zone loss in recent years.

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Expert Reaction

These comments have been collated by the Science Media Centre to provide a variety of expert perspectives on this issue. Feel free to use these quotes in your stories. Views expressed are the personal opinions of the experts named. They do not represent the views of the SMC or any other organisation unless specifically stated.

Professor Ian Rae is an expert on chemicals in the environment at the School of Chemistry at the University of Melbourne. He was also an advisor to the United Nations Environment Programme on chemicals in the environment and is former President of the Royal Australian Chemical Institute

Are we there yet?  Well, not quite but this is a good news story that's been coming for some time.  Regular monitoring first showed a decrease in the rate of growth of the ozone hole and then a 'plateau' that suggested that the being actions taken under the Montreal protocol on substances that deplete the ozone layer were doing the job.

Complete recovery will take a long time, perhaps half a century. Many of the ozone-depleting substances that we put into the atmosphere are still there and will be there for decades until natural processes destroy them.

Despite the good news, a number of ozone-depleting substances are still in use, permitted under the Montreal Protocol.    They are supposed to be destroyed or transformed on the way to producing other substances but there is always some that escapes into atmosphere and so prolongs the ozone problem.

Then there is the fumigant, methyl bromide.  Many uses of this substance have been banned under the Montreal Protocol but quarantine and pre-shipment uses are exempt. Many thousands of tonnes a year are used under this loophole and allowed to escape into the atmosphere.

Last updated: 03 Nov 2016 6:17pm
Dr Roger Dargaville is the Deputy Director of the Melbourne Energy Institute at The University of Melbourne

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.

Last updated: 03 Nov 2016 4:59pm
Dr Joseph Lane, Senior Lecturer in Physical and Theoretical Chemistry, University of Waikato

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 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.

Last updated: 03 Nov 2016 4:24pm
Dr Olaf Morgenstern, Principal Scientist - Atmosphere and Climate, NIWA

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.

Last updated: 03 Nov 2016 4:59pm

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