Ozone continues to deplete

The ozone layer that shields us from damaging UV radiation is not recovering at lower latitudes, even though the hole over the Antarctic is healing, and scientists don’t really know why.

The Montreal Protocol in 1987 was one of those rare times in human history where we saw a problem and came together to implement a global solution.  The problem was CFCs from aerosols and refrigerants that were chewing through atmospheric ozone.  The Montreal Protocol was an agreement to phase-out the use of CFCs, and was recently lauded as a success by a NASA study using statellite data that showed the ozone hole over Antarctica recovering.

In a new study in Atmospheric Chemistry and Physics, Joanna Haigh from Imperial College London and colleagues analysed data from satellite missions since 1985 to detect a long term trend of decreasing ozone in the stratosphere at lower altitudes and latitudes.

“Th potential for harm in lower latitudes may actually be worse than at the poles.” Says Joanna Haigh, “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”.

Researchers are unsure as to the cause of the decline, but suggest it could be that climate change is changing how ozone circulates in the atmosphere, carrying it away from the equator, or that very short-lived substances containing cholrine and bromine found in solvents and paint-strippers could be destroying ozone in the lower stratosphere.

So what does this mean? Here are reactions from scientists around Australia:

Bill Laurance is a Distinguished Professor 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.”

Ian Lowe is Emeritus professor of science, technology and society at Griffith University and former President of the Australian Conservation Foundation and Bragg member of the Royal Institution of Australia

“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.”

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.”

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.”

Professor Ian Rae is a  former President of the Royal Australian Chemical Institute and has been an advisor to the United Nations Environment Programme on chemicals in the environment. Ian is also an editor of the Australian Academy of Science journal, Historical Records of Australian Science

“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.”

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.”

Expert comments gathered by the Australian Science Media Centre (AusSMC)

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