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Ozone hole extent

Repairing the hole - the ozone layer and the Montreal Protocol, 24 years on

25 September 2011

We recently passed the 24th anniversary of the Montreal Protocol, which banned chlorofluorocarbons, or CFCs, until then widely used as propellants and refrigerants.

Jonathan Shanklin of the British Antarctic Survey (BAS) was part of the three-man team that first discovered the ozone hole, and that went on to write a seminal Nature paper showing CFCs were to blame. He talks to Tom Marshall about his part in the science behind a landmark environmental treaty.

TM: How did you first get involved with ozone measurement?

JS: I'd finished my undergraduate degree, and after a year of teacher training I got a job at BAS. They put me to work inputting the results of our ozone measurements at the Halley base in Antarctica - we had a lot of handwritten sheets of data that had never been systematically analysed. Others typed the data into the computer system, and my job was to check it - both that it had been entered correctly and that the original measurements made sense.

TM: I imagine nobody expected the results would be all that momentous.

JS: No! It was pretty routine work, and mostly quite tedious. At the time it was seen as just a matter of dotting Is and crossing Ts.

TM: So when did you realise something big and unexplained was going on?

JS: We were having an open day, and I thought I'd show people the latest year's findings alongside the measurements from 20 years ago. At the time there were a lot of fears that Concorde or CFCs would destroy the ozone layer. I thought if I showed them that things hadn't changed much in the last 20 years, they could stop worrying. But when I looked at the data I could see right away that things had changed a great deal.

'Without Montreal, we'd pretty much have a global ozone hole - almost everyone on the planet would have been affected.'

TM: So the idea that CFCs could be responsible for damaging the ozone layer was out there already?

JS: It was, although we didn't know how big the effect would be in practice. The theory was that if it did happen, it would be around the equator and at very high altitudes. So to find it over Antarctica and at the very bottom of the ozone layer was pretty surprising!

TM: What then?

JS: We had to go back through the data over a much longer period to make sure this wasn't just noise - just one year with low values doesn't prove anything. But it soon became obvious this was a long-term, systematic decline that we needed to explain.

Joe and Brian [Farman and Gardiner, the other two team members] started to re-examine the measurements and try to explain the steep decline. They concentrated on the atmospheric chemistry; my job was to keep providing the data. Quite quickly they managed to confirm the hypothesis that CFCs were to blame, and we published the Nature paper in 1985. The US scientists went back to their satellite data and confirmed that the ozone hole was visible there too; they'd just missed it.

TM: The Montreal protocol banning CFCs and other ozone-depleting gases was signed in 1987, just two years after your paper. That seems incredibly fast compared to how long it's taking for politicians to address climate change these days. Why do you think the science led so quickly to such a big shift in policy?

JS: For one thing, it was a much more obvious and clear-cut trend. If you looked at the satellite data showing ozone over Antarctica, it was unmissable - the decline jumped out and hit you in the face. There was almost nobody questioning whether the trend was real, which obviously isn't the case with climate change.

Nowadays, there are some places where climate change does leap out at you in a similar way if you know what to look for - on the Antarctic Peninsula for example, which is three or four degrees warmer than it was 50 years ago. When I go down there I can see the changes myself.

But in a lot of other places you can get an annual blip that fools people into thinking it's not happening - for example in the UK we've just had a very cool summer. Now worldwide, the last year has actually been one of the warmest on record, but you have to look on a global scale to see that - often local weather patterns don't suggest the world is getting much warmer.

In retrospect the name given to the problem also helped. Holes are generally a bad thing; they need filling in. Whereas the 'greenhouse effect' sounds quite pleasant to a lot of people - psychologically it's all wrong.

The other big factor was the direct link to skin cancer and other serious threats to people's health. I think this kind of danger seems much more immediate than the risk of climate change in the future.

It's also worth bearing in mind that talks for the Vienna Convention [for the Protection of the Ozone Layer] were already underway, and the convention was agreed in 1985, before we published the paper. So there was already broad agreement that the ozone layer needed to be protected; this meant that when we showed the problems CFCs were causing, we could move on to an agreement on them without too much argument.

TM: BAS is still monitoring ozone conditions over the Antarctic. How do the instruments you use these days compare to what you were using in the 80s?

JS: It's evolved a bit, but it's essentially just the same. Part of the point of maintaining a long-term dataset like this is to keep the instruments you're using as constant as possible to make sure that measurements from different periods are comparable. We've added some modern electronics here and there but in essence we are still using the same Dobson spectrophotometers at Halley as we have been since 1956, and the basic principles haven't changed since they were invented in the 1930s.

Just about every new satellite uses different instruments and gives slightly different readings, and each one's lifetime is often only five or six years, so long-running records like ours are invaluable for calibrating and checking new observations from space. Without these long-term datasets, it's impossible to look beyond the normal variation and know if things are really changing.

TM: Are there any new developments in BAS ozone measurements?

JS: We've recently started to provide daily updates on ozone conditions over the meteorological internet, and we could do it more often if needed. This kind of data is only just starting to be used, but we think it will be increasingly important for long-term weather-forecasting.

TM: Is the ozone hole now closing up?

JS: It's too early to say things are getting better, but they've certainly stopped getting worse. We'll continue our measurements at least until we can confidently say the hole will never get worse again. This might take a decade or so. There's a lot of annual variation - we'd look pretty stupid if we announced the hole was closing up based on one good year, and then had to backtrack when it increased again the following year.

TM: Is the Montreal Protocol still up to the job?

JS: The parties to it meet regularly to add new chemicals to the regulations, so the rules regularly get tightened. There's now a move to include certain greenhouse gases in the protocol because of their long-term effects on the ozone layer - it may be possible to use it to help control climate change.

TM: Montreal has to be one of the most successful pieces of environmental legislation ever.

JS: Certainly; without Montreal, we'd pretty much have a global ozone hole - almost everyone on the planet would have been affected. Many people would have got skin cancer of some kind, and everyone would have had to change their behaviour. It's amazing to think about the world we have avoided.


The United Nations Environment Programme produced a video to mark the International Day for the Preservation of the Ozone Layer (Ozone Day), on 16 September. It features interviews with several scientists involved with the discovery of the ozone hole and the creation of the Montreal Protocol, including Jonathan Shanklin of BAS. You can watch the video via the link to the right of this article.


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