Shanklin Sets the Record Straight on the Ozone Hole

By J. Brock (SARTMA-FI)

JS: Ozone measuring really began in the early1930s with the discovery that we did actually have an Ozone Layer and, for a long time, it wasn’t really known but just guessed at. And, then, an Oxford professor designed an instrument called the Dobson Ozone Spectrophotmeter. Dobson was the Oxford professor. Quite amazingly, that instrument has continued to be the world standard, even today. So it was really an incredibly designed piece of equipment.

JS: Originally the measurements were just for scientific interest nobody really knew this was of any great importance. But as they studied the records it became possible that changes in Ozone preceded changes in the weather. For that reason they started to set up a network of these instruments so they could plot the changes in Ozone and then hopefully forecast what the weather was going to do. It turned out in the end that computers became much more efficient at predicting what the weather was going to do. But the Ozone network was never disbanded and kept making the measurements. And, then in the 1970s there were suggestions that the Ozone Layer could be disappearing thanks to the effect of things like the chloro fluro carbons from spray cans and polystyrene foam and things like that and also the exhaust gasses from Concorde and other stratospheric craft. This seemed very unlikely but nevertheless, we started looking at the observations from Antarctica and we expected to see changes happening in the Autumn. That’s March, April time because that’s when the day to day changes in Ozone are the smallest. But somewhat to our surprise it turned out that the biggest changes seemed to be occurring in October when you get very large day to day changes naturally. After a bit more study it became obvious that it was a systematic change, that each year the minimum of Ozone in October was getting lower and lower and that was really the discovery of what is known as the Antarctic Ozone Hole. We didn’t know it was an Ozone hole at the time because we had point measurements over our two Antarctic stations. That was at Halley and Faraday. Halley showed the biggest change. Faraday showed a smaller change and we couldn’t possibly know whether it covered the entire Antarctic continent.

JS: Our findings were published in the Scientific magazine called "Nature." And, then the American scientists went back to their satellite data and discovered that it had been there all the time. Unfortunately they ( the Americans) had gathered so much information that they decided to do some automatic quality control and this quality control threw away values that were thought to be unlikely and, unfortunately for them, the unlikely values were the real ones that were showing low Ozone and so the Ozone Hole wasn’t seen from Space. What they were able to do was to say that it covered the entire Antarctic Continent. And, it was the American scientists that actually christened it "the Ozone Hole."

JS: Since we discovered the Antarctic Ozone Hole, levels continued to drop. This is a minimum value that we see each October. Since the early 1990s the minimum value doesn’t really seem to have got significantly lower. It’s about 2/3^rd of the Ozone Layer disappearing. We are left with just 1/3^rd of it. The reason for that is that we have taken out actually the most centre part of the Ozone Layer and there’s a bit at the top and a bit at the bottom that isn’t effected by the mechanism for its own depletion. Once you’ve taken out all the middle, you can’t get any lower than that and so values don’t drop any further. So, we think that, unless something else happens, we are not going to see dramatically lower values of Ozone but we might well see an ozone hole that gets larger.

JS: In fact, this year we saw the largest ever Antarctic Ozone Hole covering some 28 million square kilometres, which is getting on for the size of Africa. So, it’s a really huge area and quite interestingly, the Ozone Hole tends not to sit exactly over the South Pole, but offset quite often towards the Atlantic and perhaps into the Weddell Sea. And, that means, in particular, that the southern most part of South America, the Falkland Islands, South Georgia, are all much more likely to be affected by the Ozone Hole than islands on the other side of the continent. So, it’s very unlikely, really, that Australia and New Zealand in particular are ever going to be significantly affected by the Ozone Hole whereas southern South America this year was affected perhaps for over a fortnight. So, much more a significant problem for the Atlantic side of Antarctica. Eventually we think the Ozone Hole is going to cease getting bigger.

JS: It’s possible that in the past there might have been natural Ozone Holes. For example, if there was a very, very big volcanic eruption that put gasses that can effect the Ozone Layer in to the atmosphere, or a giant meteorite exploding high in the atmosphere which, again, could possibly trigger reactions that destroy Ozone. But those sort of things would only last for a year or two at most and then the atmosphere would recover again. Whereas our present Antarctic Ozone Hole is a seasonal thing that happens every Spring but it’s been going on since the early 1980s, possibly the late 1970s. So, we’ve got 20 or more years of it and that is yet another reason why it isn’t a natural phenomena.

JS: There are two things that govern the size. The first is the amount of Chlorine in the atmosphere and that Chlorine and another substance, Bromine, come from the CFCs and Halons, which are used in fire extinguishing systems. There manufacture has been banned under the Montreal Protocol. Although, developing countries were allowed to continue production for a while. Now, that ‘while’ is just about expired so that in future there should be no manufacture of these substances that deplete Ozone. And, eventually, their amount in the atmosphere will get smaller and smaller. But it’s a long, slow process and it may well be 50 years or more before we are back to conditions that existed in the early 1970s. It is going to be a serious problem for some time. That all assumes that the atmosphere itself isn’t going to change. Unfortunately, we are doing things to the Atmosphere that are making it change. We are pumping into the atmosphere Carbon Dioxide and Methane. These are called ‘greenhouse gasses’ and they are tending to warm the surface of the Earth. Higher up in the atmosphere it’s getting colder and cold conditions make it more likely that Ozone depletion can occur. There’s a special mechanism that happens in Antarctica whereby, during the Polar Winter, thin clouds actually form in the centre of the Ozone layer. Chemical reactions take place on the surface of those clouds that put the Chlorine and the Bromine into an active form so that when the sun comes up in the Spring, Ozone values drop at about 1% a day. Now, with the atmosphere getting colder, those clouds can become more wide-spread and cover a larger area and the Ozone Hole gets bigger. And, there is also the possibility that we might see something similar in the Northern Hemisphere. And, that is going to delay this process of recovery. So, it may well be more than 50 years before things recover.

JS: There are links between global warming and the Ozone Hole but they are not directly related. The Ozone hole isn’t causing global warming and global warming isn’t causing the Ozone Hole. But there are some side effects of each which make the other one worse. So, for example, Ozone itself is what is called a greenhouse gas or radiative-reactive gas and it can absorb solar energy high in the atmosphere. In fact, that’s what makes that highest most part of the atmosphere get warmer. It’s absorption of energy by Ozone. It’s that very absorption of energy that is soaking up the ultra-violet light from the sun that is stopping it getting through to the surface. With less Ozone, there is less warming high up, which means there’s a bit more warming low down. That’s one link. And, the other is, as I said, that the global warming at the surface is also a global cooling in the Ozone Layer. So, there are various links but they are not direct.

JS: One of the consequences is that more ultra-violet light gets to the surface and the immediate effect of this on people, at any rate, is to get sunburnt and you can get sunburnt very quickly when the Ozone Hole is overhead. UV levels are considerably higher than they would be on a tropical beach at midday even in the Falklands and even in Southern South America. It’s easy enough to measure the consequences on people. It’s much harder to find out what the consequences on animals are. With people, the sunburn you recover from fairly quickly but further into the future, this may well condition you for skin cancers and a long exposure to UV is likely to give you cataracts in your eyes and you eventually become blind.

The animals, if it’s a similar sort of process, you might expect skin cancers to form in 20 or 30 years. So, there is not really much point in looking for effects in animals that have a life-span of less than 30 years, because you’re not going to see anything significant. That really leaves perhaps some of the large seals and whales and it is quite difficult to do a significant sample on them. Looking at smaller things like the plant life, there is reasonably good evidence that when the Ozone Hole goes overhead the productivity of the phyto-plankton, the little organisms that generate Oxygen, or the plants that generate Oxygen on the seas, they produce less Oxygen when the Ozone Hole is overhead. Other than that, there is no clear cut evidence for damage to ecosystems in the wild. You could simulate all of this in a laboratory by shining UV light over things and the creatures and plants will definitely respond. But that’s not the same as in the natural environment. It’s difficult to say what will really happen there.

JS: In the future we need to continue with the provisions of the Montreal Protocol because that is beginning to work. It is quite a good treaty. Most of the world’s countries signed it. It’s very, very clear that CFC levels are now at their peak. It’s quite difficult to say when they will start falling but they are definitely at or near the peak. And, Without the treaty , we’d have levels of CFCs that are perhaps three times as much as they are today. So, it’s had a dramatic effect.

JS: We are starting to manufacture substitutes for the CFCs and the early ones have hydrogen in them as well as chlorine and fluorine and carbon. And, that makes them a little less stable so that they have about a tenth of the potential of damaging the Ozone Layer. But that means if we make ten times as much of them, we are still back to square one. In the longer term, those are also going to be banned and they will be replaced by substances that don’t have any chlorine or bromine in them at all and obviously that’s not going to destroy the Ozone layer so they may cause problems elsewhere. What we need to do for the future, though, is to introduce a similar protocol that limits the emission of greenhouse gasses. And, that’s going to be very much harder to achieve, simply because everybody wants to use energy and wants to use more and more energy in everyday life. But with care and by trying to eliminate wasteful uses of energy then we should be able to at least begin to achieve a reduction in these gasses.