By James Mitchell Crow of Nature magazine
The hole in the ozone layer over Antarctica is starting to heal, say researchers in Australia. The team is the first to detect a recovery in baseline average springtime ozone levels in the region, 22 years after the Montreal Protocol to ban chlorofluorocarbons (CFCs) and related ozone-destroying chemicals came into force.
Each spring, those chlorine- and bromine-releasing chemicals eat a hole in the ozone layer above the Antarctic. Thanks to the Montreal agreement, levels of anthropogenic ozone depleters detected in the region's stratosphere have been falling since around the turn of the millennium. However, detecting any corresponding ozone recovery has been difficult.
That difficulty is down to significant natural variations in average Antarctic stratospheric springtime ozone levels from year to year, which mean that the hole can be small one year and large the next. Scientists did not expect to be able to detect the gradual recovery of ozone for decades, masked as it is by these dramatic swings.
However, Murry Salby, an environmental scientist at Macquarie University in Sydney, Australia, and his colleagues have now shown how this annual fluctuation can be accounted for -- and so removed from the data. They are left with the underlying systematic change in Antarctic ozone levels. Salby's calculations reveal that the levels are now rising; the findings are published in Geophysical Research Letters.
Ice in the air
The team's breakthrough was in showing that annual swings in average springtime ozone levels are linked to changes in a particular pattern of stratospheric weather known as dynamical forcing. In years in which this phenomenon is strong during the winter, more cold air is trapped above the pole. As a result, there are more ice crystals in the atmosphere. These crystals form the surface on which chlorine destroys ozone, catalyzed by sunlight returning to the Antarctic during the spring.
"I think this is the first convincing observationally-derived evidence of the ozone rebound," says Adrian McDonald, an atmospheric scientist at the University of Canterbury in Christchurch, New Zealand. "It's the first where the statistical significance is high enough, and you can see the pattern well enough, that you feel comfortable in believing it."
Salby's results reveal a fast decline in ozone levels until the late 1990s, then a slow rebound that closely matches what theoretical calculations had predicted, says David Karoly, a climate scientist at the University of Melbourne, Australia. "It is the sort of result that was expected, but is the first to provide detection of an increase in Antarctic ozone levels," he says.
Adding weight to Salby's argument, the increase in ozone levels revealed by the calculations closely mirror the decrease in the levels of anthropogenic chlorine in the region. "For now, they agree pretty well," says Salby. "My feeling is that as time goes on we will start to see other influences on the systematic evolution of ozone level beside chlorine." One such influence is likely to be the increasing concentration of carbon dioxide in the atmosphere.
Slow change
Salby's data reveal that average springtime Antarctic ozone levels have already recovered by 15% since the late 1990s. However, projecting forward, natural weather-related fluctuations mean that even as late as 2085, ozone will still drop below 1980 levels for at least one year in every ten.
A complicating factor in that prediction is the influence of climate change, says Karoly. "Even when CFCs are removed, ozone levels will be different in the future than they were in the 1960s, because of changes in temperature in the stratosphere."
It's a relationship that goes both ways, however. "In the past four or five years it has become very clear that the ozone hole seems to have held back climate change over Antarctica," says McDonald. Ozone absorbs sunlight, so less ozone means the stratosphere heats up less. This has caused a change in circulation patterns around the Antarctic, which has trapped more cold air over the pole. As the ozone hole recovers, its future impact on Antarctic climate, and so on melting ice caps and global sea-level rise, is under debate.
"Some people are saying that, once the ozone hole totally recovers, because it has so far had a braking effect, maybe when that brake gets taken off then we'll have rapid change over the Antarctic. But there are many complexities in the system, and so other people are saying that it might not have very much effect. That is definitely work to be done by the climate-science community."
In the more immediate term, the strong correlation between winter weather patterns and springtime ozone levels means that the intensity of the ozone hole can now be forecast, says Salby. That is important because, at the end of each spring, the ozone-depleted air is released across the mid-latitudes of the southern hemisphere, affecting major population centers during the summer months by allowing increased levels of ultraviolet light to reach Earth's surface.
"If you know what the stratospheric forcing is during the winter, you can predict rather accurately the ozone level for the following spring," says Salby.
This article is reproduced with permission from the magazine Nature. The article was first published on May 16, 2011.
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5 Comments
Add CommentThe ozone depletion problem that we faced in the 1980s is proof that mankind can have a dramatic effect on the environment on a global scale. The Montreal Protocol and the quick elimination of ozone-depleting compounds is proof that the world's countries can work together to solve major environmental problems. That the companies that used to produce CFCs are still very profitable is proof that all their bellyaching about government regulations and interference was overblown.
Reply | Report Abuse | Link to thisThe CFC makers, along with the sulfur dioxide emitters that were subject to emissions trading under the Acid Rain Program, made a desperate case that they would all go out of business if they were forced to clean up their act. The costs of these regulations were overstated by at least 500%. This is a valuable lesson to remember when all the CO2 emitters complain about the costs of reducing their pollution while they say nothing about the cost of inaction.
Sault,
Reply | Report Abuse | Link to thisYou are very optimistic about our current political environment. If regulations on both CFCs and SO2 were to come to vote today, there is no way they would pass. Republicans would say they are job killers. Libertarians would say its socialism and strips our freedoms. Ironically, cap and trade is a Republican idea. This entire climate debate is purely politically driven. Ironically, it was probably Al Gore who started it. I wonder if reverse psychology would work: Democrats begin saying that global warming is a myth.
They will do whatever it takes to gain political power. Whether it is being financed by Big Oil, Wall Street and the Koch brothers; or lying about facts; or demonizing and opposing their opponents on every issue.
Case in point in the last 24 hours: Newt Gingrich said yesterday on Meet the Press that he was for a health insurance mandate for each individual. Today he said he was against a mandate. A few weeks ago he was for the Paul Ryan budget (against a mandate). Yesterday, he was against the Ryan plan. In 1993 he was for a health ins mandate.
Do you really think they will do what's best for the country or the world? It is just doing the opposite of your opponent, then pumping out the propaganda through Fox News.
I don't think you understand the point. Yes of course the internal combustion engine produces toxic emissions but due to their economy we've found that their benefits have outweighed their costs so far at least. There was a much easier switch for the chemical industry and as Sault pointed out they are still making nice profits on refrigerants. Perhaps there will come a day when there's a more economical and environmentally friendly engine than the most fuel efficient engines today but that hasn't come yet.
Reply | Report Abuse | Link to thisI agree. The Right has already advocated for stripping the EPA of the power to reduce mercury, ash and acid gas emissions from power plants / industrial boilers. They value profits for their corporate masters over the health and wellbeing of the American public.
Reply | Report Abuse | Link to thisIn reality, I'm not very optimistic on the chances of having meaningful progress on envronmental/energy issues (or any issues for that matter) until the next congress gets seated in 2013, and that's ONLY if its radical right-wing members get defeated in the upcoming elections.
We have seen their real agenda since they're not even trying to hide it now. The House of Representatives has passed a bunch of symbolic legislation concerning Culture War issues that have NOTHING to do with the economy or the budget and one lone bill designed to destroy Medicare while funneling even more money to the wealthiest 1% of Americans. We've tried the supply-side, free market fundamentalism for over 30 years now and all it did was stagnate incomes for the bottom 90% of income earners while exploding the defecit each time taxes were cut.
Question for the editors at SciAm -- can you follow up on this story? When I first read it it seemed reasonable.
Reply | Report Abuse | Link to thisAfter looking at Prof. Salby's other public comments, I wonder if he's speaking politically rather than scientifically, e.g. http://www.google.com/search?q="murry+salby"
A a deep ozone loss in the Arctic was reported after this article came out. How does this make sense? Are there other reports supporting or questioning his statement?