The Antarctic ozone hole - 25 years on

Diagram showing extent of ozone hole over Antarctica

16 March 2012 by Jonathan Shanklin

Richard Hollingham met Jonathan Shanklin in Cambridge to find out more about the discovery and why the hole is still there.

Richard: Jonathan, you were doing your research at the British Antarctic Survey's Halley Research Station on the Brunt Ice Shelf in Antarctica when you made your discovery. And you've got one of the original hand-drawn graphs with you showing the drop in ozone levels over time.

Jonathan: Yes, we've got the data from Antarctica which I'd plotted up and one of the key things was that we could see something going on in our data.

Richard: So, let's look at this graph. It's plotted by hand at a time before computers could even do this.

Jonathan: Yes, drawn on paper with a pencil and a ruler to draw the best-fit line through the data. But the point is, anybody can see that something is happening. You can see ever so clearly that ozone amounts are going down and that was absolutely key: once you could see something this systematic, then something must be causing it. My question was: what?

Richard: So then you made a correlation between this decline in ozone and CFCs?

Jonathan: Yes. People had speculated for some time that CFCs could affect the ozone layer, but they predicted it would happen high above the tropics. What we found was an effect low in the atmosphere, above the Antarctic; quite a different place. But because there was an expectation that CFCs could affect the ozone layer, we thought that was probably what was happening, and so then we plotted the graph. At a glance, you could see that there was a correlation between ozone amounts declining and CFC amounts going up.

Richard: OK, so the Montreal Protocol is a huge success in terms of environmental treaties, getting that done just two years after your discovery. Why, then, is there still an ozone hole over the Antarctic?

Ozone founders Joe Farman, Brian Gardiner and Jon Shanklin

From left: Joe Farman, Brian Gardiner and Jon Shanklin. The instrument is a Dobson ozone spectrophotometer, used to determine stratospheric ozone concentrations.

Jonathan: The Montreal Protocol has been incredibly successful. But these CFCs are very stable. They stay in the atmosphere for a long time. So, although the amounts of CFCs in the atmosphere are dropping, there are still so many up there that when conditions are right you'll still get ozone destruction. Unfortunately you get those conditions over Antarctica every year, and this year we've had one of the deepest and largest ozone holes on record.

Richard: When you first plotted the graph and published your findings in Nature, could you have imagined that it would lead to the Montreal Protocol?

Jonathan: When we first made the discovery we thought, well, this is a pretty obscure part of the world, it's not going to have a global impact by any means. But it is a lesson in how quickly we can change our atmosphere. Between ozone depletion being detectable to it being a full-blown ozone hole happened in the space of about a decade.

Richard: The Montreal Protocol was a huge success when it comes to these sorts of treaties. Can this be repeated when it comes to global warming, to climate change?

Jonathan: There are differences. With CFCs, just about everyone was on side. The manufacturers were quite happy to switch to a different product, and it was very easy to do. Also the public don't like 'holes', so calling it a hole struck a chord. Then there was the link between increased ultraviolet light and cancer; cancer is one of the banes of today's society, so if something is causing it we've got to get rid of it. So everything worked in favour of doing something about the ozone hole.

With greenhouses gases, it's much harder. First of all, 'global warming' sounds nice. Secondly, it'll take a very big change in people's lifestyles to reduce their dependence on fossil fuels.

The oil industry in particular is rather reluctant to stop selling oil. There's no cheap alternative that could be widely sold. I think we will be lucky to get a treaty that's as effective as the Montreal Protocol was.

Jonathan Shanklin is an atmospheric scientist at BAS.

This Q&A is adapted from the Planet Earth Podcast 22 November 2011.