Credit: NASA's Earth Observatory

EXPERT REACTION: Ozone levels still decreasing away from poles

Embargoed until: Publicly released:

Ozone levels are still decreasing at latitudes between 60⁰N and 60⁰S, which includes everything from Russia in the north to the Southern Ocean below Australia in the south, according to international research. While ozone levels in the upper atmosphere near the poles have been recovering in recent years, this new research has found that the bottom part of the ozone layer at more populated latitudes is not recovering. Although they don't have an explanation of exactly why, the researchers suggest that blame may rest with climate change or other shorter lived ozone destroying chemicals found in solvents and paint strippers.

Journal/conference: Atmospheric Chemistry and Physics

Organisation/s: Imperial College London, UK, Physikalisch-Meteorologisches Observatorium Davos World Radiation Center, Switzerland

Funder: William T. Ball and Eugene V. Rozanov were funded by the SNSF project 163206 (SIMA)

Media Release

From: American Geophysical Union

Press Release: Ozone at lower latitudes is not recovering, despite Antarctic ozone hole healing

The ozone layer – which protects us from harmful ultraviolet radiation – is recovering at the poles, but unexpected decreases in part of the atmosphere may be preventing recovery at lower latitudes, new research has found. The new result, published today in the European Geosciences Union journal Atmospheric Chemistry and Physics, finds that the bottom part of the ozone layer at more populated latitudes is not recovering. The cause is currently unknown.

Ozone is a substance that forms in the stratosphere – the region of the atmosphere between about 10 and 50 km altitude, above the troposphere that we live in. It is produced in tropical latitudes and distributed around the globe. A large portion of the resulting ozone layer resides in the lower part of the stratosphere. The ozone layer absorbs much of the UV radiation from the Sun, which, if it reaches the Earth’s surface, can cause damage to DNA in plants, animals and humans.

In the 1970s, it was recognised that chemicals called CFCs, used for example in refrigeration and aerosols, were destroying ozone in the stratosphere. The effect was worst in the Antarctic, where an ozone ‘hole’ formed.

In 1987, the Montreal Protocol was agreed, which led to the phase-out of CFCs and, recently, the first signs of recovery of the Antarctic ozone layer. The upper stratosphere at lower latitudes is also showing clear signs of recovery, proving the Montreal Protocol is working well.

However, despite this success, scientists have today revealed that stratospheric ozone is likely not recovering at lower latitudes, between 60⁰N and 60⁰S (Berlin is at 52⁰N), due to unexpected decreases in ozone in the lower part of the stratosphere.

Study co-author Joanna Haigh, Co-Director of the Grantham Institute at Imperial College London, said: “Ozone has been declining globally since the 1980s, but while the banning of CFCs is leading to a recovery at the poles, the same does not appear to be true for the lower latitudes.

“The potential for harm in lower latitudes may actually be worse than at the poles. The decreases in ozone are less than we saw at the poles before the Montreal Protocol was enacted, but UV radiation is more intense in these regions and more people live there.”

The cause of this decline is not certain, although the authors suggest a couple of possibilities. One is that climate change is altering the pattern of atmospheric circulation, causing more ozone to be carried away from the tropics. The other possibility is that very short-lived substances (VSLSs), which contain chlorine and bromine, could be destroying ozone in the lower stratosphere. VSLSs include chemicals used as solvents, paint strippers, and as degreasing agents. One is even used in the production of an ozone-friendly replacement for CFCs.

William Ball from ETH Zurich and PMOD/WRC Davos, who led the analysis published in Atmospheric Chemistry and Physics, said: “The finding of declining low-latitude ozone is surprising, since our current best atmospheric circulation models do not predict this effect. Very short-lived substances could be the missing factor in these models.” It was thought that very short-lived substances would not persist long enough in the atmosphere to reach the height of the stratosphere and affect ozone, but more research may be needed.

To conduct the analysis, the team developed new algorithms to combine the efforts of multiple international teams that have worked to connect data from different satellite missions since 1985 and create a robust, long time series. “The study is an example of the concerted international effort to monitor and understand what is happening with the ozone layer; many people and organisations prepared the underlying data, without which the analysis would not have been possible,” Ball said.

Although individual datasets had previously hinted at a decline, the application of advanced merging techniques and time series analysis has revealed a longer term trend of ozone decrease in the stratosphere at lower altitudes and latitudes. The researchers say the focus now should be on getting more precise data on the ozone decline, and determining what the cause most likely is, for example by looking for the presence of VSLSs in the stratosphere.

Justin Alsing from the Flatiron Institute in New York, who took on a major role in developing and implementing the statistical technique used to combine the data, said: “This research was only possible because of a great deal of cross-disciplinary collaboration. My field is normally cosmology, but the technique we developed can be used in any science looking at complex datasets.”

The study was conducted by researchers from institutions in Switzerland, the UK, the USA, Sweden, Canada and Finland, and included data gathered by satellite missions including those by NASA.


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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.

Emeritus Professor Brenton Lewis is from the Research School of Physics and Engineering at The Australian National University

As stated in conclusion (iv) of the paper, "there is no significant change in total ozone column density between 1998 and 2016".

Therefore, there will have been no corresponding increase in harmful UV radiation at ground level, and people need not be concerned. The authors are engaged simply with explaining a change in the distribution of ozone in the atmosphere, which may well be due to transport mechanisms only.

This is not to say that continued studies are unnecessary.

Last updated: 05 Mar 2018 4:51pm
Professor William Laurance is director of the Centre for Tropical Environmental and Sustainability Sciences (TESS) at James Cook University

This study is scary. Until we understand what’s really happening you’d be silly to sun yourself, except in polar regions.

The era of suntanning could be over; we might be entering the age of the unfailing sunburn.

Last updated: 05 Mar 2018 4:50pm
Ian Lowe is Emeritus professor of science, technology and society at Griffith University and former President of the Australian Conservation Foundation

The World Scientists' Warning to Humanity, Second Notice, published in November, noted that only one environmental indicator has significantly improved since 1992.

The amount of ozone-depleting substances has been reduced dramatically, from about 1.5 million tonnes of chlorofluorocarbon (CFC)-equivalent to 0.3 million. It has not been reduced to zero.

The reduction in the rate of release of these chemicals has halted the worsening of ozone depletion, but we are not yet seeing significant repair.

This paper also shows that the system is complicated and there are still aspects we do not understand well enough to model the observed data. It should be another urgent reminder that we must scale back our assault on natural systems if we are to achieve our stated goal of living sustainably.

Since we have known for more than forty years that a group of chemicals weakens the ozone layer, which protects all life from damaging ultra-violet radiation, phasing these chemicals out completely should be a high priority.

Last updated: 06 Feb 2018 10:55am
Professor Ian Rae is an expert on chemicals in the environment at the School of Chemistry at the University of Melbourne. He is also an advisor to the United Nations Environment Programme on chemicals in the environment and is former President of the Royal Australian Chemical Institute.

We know that the worst ozone-depleting substances are chlorofluorocarbons (CFCs) and other volatile chemicals containing chlorine or bromine. Emissions of these substances have been drastically reduced by international agreement, under the Montreal Protocol, to ban or restrict their production and consumption. As a result (we'd like to believe), the decline in the stratospheric ozone concentration has been arrested and there are some signs of recovery.
However, given the steep decline in emissions, we might have expected a better result for the ozone layer. This analysis of research results, published by an international group of scientists, help us to understand why we haven't. In short, the outcome is a curate's egg: good in parts.
Measurements of ozone concentration are made for a notional column of air stretching up from about 10 km above earth's surface to about 50 km. As an aside, it helps to use round numbers to convey the message because there are variations with seasons and with latitude - position on the earth.
For the column as a whole, there has not been much change in ozone concentration during the period 1998-2016. When results for 'slices' of the air in that column were examined, a more complex picture emerged. In the upper stratosphere (32-48 km), there has been a steady increase in ozone concentration, which is what was expected from the actions taken under the Montreal Protocol.

However, in a lower slice of the air column(13-24 km), there has been a continuous decline. The reasons for this decline remain unknown. Unlike the positive change at higher levels, this negative is not predicted by models of atmospheric chemistry.
The result of their analysis is nicely summed up by the authors: "We find that the negative ozone trend within the lower stratosphere between 1998 and 2016 is the main reason why a statistically significant recovery in total column ozone has remained elusive."

In colloquial language: if you add a positive change and a negative change, you get zero change.

Last updated: 06 Feb 2018 10:52am
Dr Paul Read is at the Melbourne Sustainable Society Institute at the University of Melbourne

Although the authors suggest otherwise, this paper could be a challenge to the effectiveness of the Montreal Protocol.

Ozone, like atmospheric carbon, is critical to maintaining the survivability of Earth's solar budget - all of life depends on them being maintained in a tight range. Ozone we need; too much atmospheric carbon we don't.

This is because energy from the Sun comes in three types - per kilowatt, 32 watts is ultraviolet (UV), which destroys DNA, 445 watts is visible light, and 526 is infrared, the stuff you feel as heat.

Whereas a thin film of ozone protects us from the DNA scrambling effects of UV, a growing film of carbon emissions lets infrared waves in but then traps them, causing the Greenhouse effect.  As for ozone, most people know that our wholesale use of chlorofluorocarbons (CFCs) amassed in the atmosphere and created a hole in the ozone layer that was then exposing us to cancer-causing UV light.

For fear of skin cancer, Australian beach culture changed overnight - the 'slip slop slap' campaign, the invention of rashies, etc. It took a whole world effort to ban CFCs - every country and every industry - and we went, for example, from spray cans to roll-on deodorant pretty quick smart.

The Montreal Protocol banned CFCs and was the world's first universal agreement to cooperate on behalf of global human health. Kofi Annan said it was a great sign of hope that the world could be civilised enough to do the same for climate change; estimates say it's already saved many more than 280 million lives.

What this new paper is saying is that the hole in the ozone layer, predicted to be completely repaired by around 2060, has a whole section that's not repairing itself. And they want to know why!

The section in question is about 20 kms above Earth, between the tops of clouds and the height where aeroplanes cruise, and extends from just outside the Arctic circle to the start of Antarctica.

Even though the polar regions and the higher stratospheric levels of ozone are repairing themselves, this lower, middle section is going in the opposite direction - the amount of ozone is still falling just like it was before the Montreal Protocol.

A million things could be causing this, some natural, some not. But this paper tries with all its might to get around a host of past problems to see the real trend - and the ozone is definitely falling in that region, even after seasonal, time series and measurement adjustments.

After eliminating the obvious, they're still left with some disturbing possibilities: did we underestimate the anthropogenic effect, the volcanic effect, or is there some missing chemistry? 

What they propose are three explanations related to climate change: firstly, an expanded troposphere; secondly, an accelerating Brewer-Dobson circulation; or thirdly, a disproportionate acceleration of it closer to the tropopause. In other words, the ozone is being transported out of this section faster.

If so, it's a worry because it means the actual repair might be due to more rapid accumulation in the higher stratosphere, rendering the Montreal Protocol targets perhaps too lax from the beginning, that is, unless the higher stratosphere is actually doing the lion's share of protecting us from UV radiation.

This paper suggests climate change is interfering with the ozone system as well, creating a scenario where the Montreal Protocol, although still necessary, might not yet be sufficient, for repair by 2060.

Last updated: 06 Feb 2018 10:51am
Professor Steven Sherwood is ARC Laureate Fellow at the ARC Centre for Climate System Science and UNSW Climate Change Research Centre

This finding is very interesting for scientists but I don’t think it has any broader significance yet.

The authors do not call into question the prevailing view that the ozone layer is entering a recovery phase after the damage caused in the 1980’s and 90’s by refrigerant gases, which were phased out by the Montreal Protocol.

They do find a curious ozone decrease in a particular altitude range below the main ozone layer, which suggests that changes to the atmospheric circulation may have happened up there. The community will have to look at this more carefully before we know what it means.

Last updated: 06 Feb 2018 10:45am

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