Titans of Science: Susan Solomon
Today's Titans interview is with the key figure in one of science's modern triumphs. Susan Solomon and her team were the first to theorise and prove what was causing the hole in the ozone layer above the Antarctic, and why it was growing: chlorofluorocarbon pollutants humans were emitting. What followed is a testament to what can be achieved in the face of significant challenges with international collaboration. What lessons does it hold for how we tackle climate change?
In this episode
00:48 - Susan Solomon: Finding the hole in the ozone layer
Susan Solomon: Finding the hole in the ozone layer
Susan Solomon
On today's edition of Titans of Science, we're going to hear from Susan Solomon at the National Oceanic and Atmospheric Administration. Susan is an atmospheric chemist and she was one of the first people in the world to respond to reports in the early 80's of deterioration of the planet's ozone layer. She joined the faculty at MIT in 2011 where she serves as the Ellen Swallow Richards professor of atmospheric chemistry and climate science. She's frequently cited as one of the most important women in science, and in 2008 was selected by Time Magazine as one of the top 100 most influential people in the world. Time went on to say, 'All scientists like to believe they will leave the world better than they found it. Susan Solomon surely will. Having helped save the Earth's atmosphere already, she's now playing a role in trying to do it again.'
Chris - Susan, welcome to the programme. Pleasure and a privilege to have you with us. The first thing that you did for the atmosphere concerned the ozone layer, and a hole that turned up therein. How is the health of the ozone layer now?
Susan - Well, the ozone layer is really the world's signature environmental success story. We have already seen the chemicals that were causing the ozone depletion to start dropping and drop quite a bit, and we've actually seen the Antarctic ozone holes start to get a little bit smaller and form a little bit later, particularly in the month of September. So that's a huge win. It would've been so much worse by now if we had not stopped using those dangerous chemicals.
Chris - It's so nice to start a piece like this with some good news that we're going to tell people about, and maybe we'll change that later on. But let's back up very slightly. What is the ozone layer? The clue is in the name, obviously, but what does it do for us and why does it matter?
Susan - The evolution of life on this planet wouldn't have happened until the ozone layer actually evolved. So ozone is a form of oxygen that has a somewhat different structure. Instead of having two oxygen atoms together, it's got three, and that allows it to absorb certain wavelengths of ultraviolet light that would otherwise make it all the way down to the ground. And as anyone who's ever been sunburned knows, we really need to be careful about ultraviolet.
Chris - Where is the ozone layer?
Susan - Most of the ozone layer is located between about 12 and 30 kilometres above our heads. So there's not much ozone in the lower atmosphere, and that's a good thing because ozone is actually quite toxic when you breathe it. You want it up in the upper atmosphere protecting you from ultraviolet, but you don't want it down at the ground in the air that you're breathing. People who had to breathe it in smog episodes, for example, in Los Angeles in the 60's and 70's, or even now in places like India, really do suffer. We want it up there, we don't want it down here.
Chris - And how did it come to light that ozone had a problem?
Susan - Well, the earliest work highlighting the idea that the ozone layer might be in danger actually goes back to the mid 1970's when two chemists pointed out that we were using these dangerous chemicals in larger and larger amounts, and the concentrations were building up in the atmosphere and that they could destroy ozone. The idea that something could last in the atmosphere for a hundred years was critical to that concern and people began to be concerned that if we kept using these compounds, we might see a few percent depletion or loss of the ozone layer in about a hundred years. It was a small change, far in the future - It was kind of a future problem if you want to call it that - but then in 1985 the British Antarctic Survey discovered the Antarctic ozone hole, which was a huge surprise. We didn't expect to see big ozone losses that early over Antarctica. You lose not a few percent, but more like 50% of the total amount of ozone over your head. That protective layer is reduced by a massive fraction and we didn't expect it in Antarctica. So it was a huge mystery, initially.
Chris - It was Jonathan Shanklin and Brian Gardiner and others who spotted that, wasn't it, that hole?
Susan - Yes. And Joe Farman who unfortunately is no longer with us, but they did some amazing work there. They managed to show something that the satellites had not seen, which was quite a shocker to the science community. The truth of what they said has obviously stood the test of time and then some.
Chris - When we say hole, is it really a hole and how big is it?
Susan - Well, it's a 50% loss of ozone. It's not 100%. So that's good news in a way. But the reason that it is 50% is that in a layer between about 14 and 24 kilometres, there is indeed a hole. The ozone is completely gone in that layer. So the half that you have left is only what's above and below that region where it's completely gone. The reason that it began to be called the hole is how dramatically it looks isolated when you look at it on satellite imagery. The reason for that is that the antarctic atmosphere, you can think of it as being kind of like a whirlpool, literally what we call a vortex, but think of a whirlpool like when you drain your bathtub or whatever. That keeps the air inside the middle of the whirlpool very isolated and the ozone just gets eaten away and eaten away and eaten away. So it does look like a hole. It's a very big hole. It's twice the size of the continental United States.
Chris - Does it actually extend beyond the margins of Antarctica?
Susan - Slightly, yeah, it's about 25 million square kilometres at its height in a bad year.
Chris - Are we just fortunate in a way that because of the geography of Antarctica with that polar vortex, that whirlpool that has concentrated the chemicals that are depleting the ozone down there, and we can perhaps come onto that in a minute. Is it convenient and fortunate that it's happened there where there aren't so many people, just research scientists chiefly and holidaymakers, and not over more populated parts of the planet?
Susan - Yes but I'll hasten to add that we also see significant ozone losses over the Arctic where there are a lot more people. We also see significant ozone losses over mid-latitudes, both southern and northern mid-latitudes. So although the ozone hole can be thought of as like the canary in the coal mine, it showed us first that there was going to be a big problem. Not too long after that we started measuring bigger changes at other latitudes than what we expected to.
07:53 - Susan Solomon: Chemistry of the ozone hole
Susan Solomon: Chemistry of the ozone hole
Susan Solomon
Chris - Can you talk us through what the chemistry of the ozone hole is? Because you alluded to the fact there were some toxic chemicals that those scientists pointed out in the 1970's as a possible future problem, that they could be storing up trouble. But what were those chemicals and what is the mechanism by which they degrade ozone and why specifically concentrate down in Antarctica?
Susan - Most of the problem comes from chlorofluorocarbons and, interestingly enough, these molecules were being used in large amounts in things like refrigeration, air conditioning, foam blowing, and especially as the propellants in spray cans. So back in the 1970s, actually about 75% of the global use of these molecules was in hairspray and underarm deodorant of people all around the world. The idea that it was building up and building up every year, that it had a hundred year lifetime and it might deplete the ozone layer someday, was enough to actually motivate the American public to give up spray cans. What happened was that hairstyles changed and people literally went on the stick to save the ozone layer. They started using stick deodorant. It's also really interesting that this country was really first on that, the American consumer gave up these chemicals before there was even any regulation. That was mainly motivated by the environmental groups urging people to do that and people voluntarily did it. It really shows you the power of public opinion and the power of the consumer on certain environmental problems when you can in fact take action and we can take action on all kinds of things in my view. But certainly in this case the action was huge because 75% of the market is a real punch in the stomach to any industry. The American chemical industry certainly took note of that.
Chris - Ironically, in a programme talking about atmosphere and air quality, I think even asthma inhalers were using CFCs, these chlorofluorocarbons, to propel the drugs down the lungs of people who had airway problems, weren't they? But I think you are referring to the Montreal protocol and treaty 1986 which led to a massive reduction in use worldwide of these chemicals. But why are they so bad for ozone? Do we understand what they do to the ozone to make it fall apart so we get a hole in the first place?
Susan - Yeah, we certainly do. It took us a few years, but actually remarkably only a few years. I think the whole scientific community deserves a lot of credit for being so fast and figuring this out after the British pointed it out. The way it works is that Antarctica really is the coldest place on earth. It's so cold that clouds form in the very dry Antarctic stratosphere. The stratosphere is dry everywhere and normally we don't have clouds at stratospheric altitudes. We have them down here in the lower atmosphere, but you don't get them where the ozone layer is normally. You get them very frequently in the Antarctic and sometimes in the Arctic. It's just much less common to get the frequency of polar stratospheric clouds being as much in the Arctic as it is in the Antarctic. So the coldest place on Earth with all those clouds provided a surface for chemistry to happen that simply doesn't happen when all you have are gases. That fundamentally changed the extent to which these compounds could deplete ozone. So it's not that there's more chlorofluorocarbon down there than anywhere else, it's just that it's more potent because of this surface chemistry on those cloud particles.
Chris - It's also seasonal, the hole, isn't it? We see headlines that this year it's grown, then it's shrunk a bit. Why is it seasonal?
Susan - That is such a cool thing. So you need not only cold temperatures, but you also need sunlight to drive the chemistry that's involved. That's a little complicated. The main point is that the air, when it's cold and dark, the chemistry just can't get cranked up. What happens is that the chlorine on the surfaces of these clouds makes a molecule called Cl2, which is actually chlorine gas. It's a very strong absorber of any kind of light. It Immediately breaks it down and those chlorine atoms then go on and destroy ozone and some further reactions. But that's why you need sunlight as well as cold temperatures. Then, when it gets too warm, the chemistry can't happen anymore. So basically it's sort of a goldilocks effect where you need a combination of cold and light and you get that sweet spot right in the Antarctic in their spring which, because it's the southern hemisphere, is August and September, not what we would think of like February and March in the Northern Hemisphere. We do see ozone depletion in the Arctic to some extent in February and March too but nothing like the Antarctic in almost all years.
Chris - You mentioned, and it was a surprise to me because I hadn't heard that before, that we're also seeing ozone depletion at other latitudes, not just down on the South Pole. You just mentioned the Arctic. If it's down to temperature, that's not going to be the case at these other latitudes so much, is it? So how do we account for that loss?
Susan - Well, these surface reactions happen to a limited extent everywhere. Fundamentally, that's a big part of this and there's also some mixing of the ozone depleted air from the Antarctic down to, say, New Zealand and Australia. Same thing happens in the Arctic: there's some communication of that depleted air, and the gases are also doing some loss of ozone, but it is mostly that surface chemistry operates to a more limited degree at warmer temperatures.
14:08 - Susan Solomon: Climate change and the ozone layer
Susan Solomon: Climate change and the ozone layer
Susan Solomon
Chris - How do we expect then that climate change will influence this? Do we think that if we push temperatures up then this makes things worse in the Antarctic or will it make things better? So we have to suffer a hotter climate, but we get our ozone back?
Susan - Boy, that is a fantastic issue. It turns out that although carbon dioxide and the other greenhouse warming agents warm the lower atmosphere, they actually cool in the stratosphere. So the sign of the impact of increasing carbon dioxide actually flips. We have great satellite data now that shows unequivocally that we have cooling of the stratosphere that is due to the greenhouse gases. So if anything, that effect would make it slightly worse. It's not big enough to have an enormous effect and, in the Antarctic, you're already way colder than you need to be to make these clouds. So the effect is not large there. Where it might have a bigger effect is actually in the Arctic because you're right on the edge in the Arctic. So ironically, the fact that climate change agents warm the lower atmosphere but cool the upper atmosphere would actually make the ozone loss potentially worse. Another thing that's come up recently is the impact of wildfires. There's pretty good evidence that wildfire smoke from the Australian fires actually impacted the chlorine chemistry at mid-latitudes over Australia in a way that's surprisingly similar to what happens only at cold temperatures on the polar stratosphere clouds that are normally there. It's just a different kind of particle that can do different chemistry. It's really amazing how clear cut the satellite data on this actually are. I think the whole community now is wondering as we go forward into this 21st century and things get a little bit warmer - hopefully before we start to turn it over and stop warming - but we probably will get a little bit warmer and we are seeing more wildfires. To what extent could that actually affect the recovery of the ozone layer is a very interesting question. One that I'm actually working on right now.
Chris - Why do we still have a hole, though? Because it will soon be four decades since it was confirmed and we launched one of the most successful environmental protocols that's ever been launched that you allude to, that people responded like we've never seen people respond before, and industry too. Why is the hole still there though? Is it that we are seeing the legacy effect of what damage we did do and it's just going to take a long time for those chemicals to disappear? Or has something else taken over as the source of the toxic chlorine that dismantles ozone?
Susan - As was said in the 1970s, these molecules that are causing the problem really do have long lifetimes in the atmosphere. These chemicals last anywhere between 50 and in some cases even as much as 500 years. The stuff that I used when I sprayed my hair when I was a teenager in the early 70's, some of it is still here and that's kind of amazing, but that's what happens when you talk about a chemical with a long atmospheric lifetime. It's still here chewing up the ozone layer and makes me think about every time that I do something that produces a long-lived chemical: what really is my impact on this planet.
Chris - Even CO2 has a long lifetime in the atmosphere doesn't, it? It's measured in centuries. When you light a match, the CO2 that's coming off the end of that match is going to be around for a lot longer than we are. It's also extraordinary, just listening to what you're saying about the legacy effect of chemicals that hang around for a long time, that really the writing was on the wall for these chlorine based chemicals, and yet we've gone ahead making what we now dub persistent organic fluorocarbons and these alcohol groups and things which make plastics feel nice and make our paper so we can put greasy things on it and not get greasy fingers. They're now being found all over the planet, yet we continue to produce them in prodigious quantities. It seems strange that we've gone from poisoning the air to poisoning the planet elsewhere.
Susan - I am always concerned when I see that we're thinking about things that are persistent because we've made so many mistakes with them in the past. It's not just chlorofluorocarbons with their 100 year lifetimes. Think about DDT for example. DDT had about a 20 year lifetime in soils and people just didn't realise that by using it as a pesticide year after year, building up and building up and causing tremendous damage to wildlife, especially the deaths of the robins back in the 60's, were what prompted people to realise that persistent pesticides were dangerous. Nowadays we're talking about persistent fluorinated compounds, PFAS compounds. We are lucky in one respect, fluorine does not deplete the ozone layer, unlike chlorine. It's not a risk to the ozone layer, but certainly these compounds are everywhere and they're building up in our bodies and the ecosystem and there's a lot of questions about how dangerous they are and they'll be with us for a long time. Plastic of course is the same problem. Plastics have lifetimes of many hundreds if not a thousand years, depending on what kind you talk about. They do break down to make microplastics and even nanoplastics, but it's pretty frightening how many little pieces of microplastic are in a plastic water bottle. This is all going into our bodies. We don't know what happens to it.
Chris - Time magazine said you had saved the planet once, now you are trying to do it again. Are they referring to the fact that we've moved beyond ozone and we realise that we have a really big problem with carbon dioxide now?
Susan - Yes. I had the honour of being part of the intergovernmental panel on climate change the year before Time magazine cited me, working with 150 wonderful scientists from around the world to produce a report for the world that had the statement 'warming is unequivocal' as its key finding. Those words I think have resonated and are still part of why people are so concerned. The evidence that we are warmer is now so clear that climate deniers don't really try to pretend that it's not warming anymore. They tried that method for a while, they could get away with it, but that's just not going to work now. Too many observations and people's own perceptions that summers are hotter and extreme heat waves are hotter than they were before in many parts of the world. Not everywhere, but in surely an overwhelming number of places.
Susan - So, yes, I've been also involved in climate change. You mentioned the issue of the lifetime of carbon dioxide in the atmosphere, which is also one that I've worked on and what the implications of that are for warming and it's really bad news, there. Most of it does go away on a timescale of maybe 150 years. That's actually comparable to the chlorofluorocarbons we've been talking about for the ozone layer. But some of it stays in the atmosphere - about 20% of it actually - for about a thousand years or more. So every time that you drive your car, your gasoline powered car that is or, as you said, light a match, you're adding stuff to the atmosphere that will be here for a very, very long time and cause warming.
21:46 - Susan Solomon: 3 P's to save the planet
Susan Solomon: 3 P's to save the planet
Susan Solomon
Chris - One of the points you made earlier was the huge response from the public and industry to CFCs, the hole in the ozone layer. Now that hole in the ozone layer was not going to affect most of the people who reacted there and then, but they did react and we got one of the most successful treaties ever out of that. Why have we, despite the demonstrable evidence that we have got a climate problem, why do you think we are seeing such a lot of inertia? Is it that it's such a hard nut to crack? Throwing away a few aerosols was relatively easy compared to completely changing our lives because we had become so addicted to a carbon-based source of energy. Is that the reason?
Susan - I think that's part of the reason. The other thing is that we're late to the party a little bit here because it wasn't as obvious initially. I think that people become concerned about an environmental problem when two P's are satisfied. They have to think that it's personal to them and they have to think that it's perceptible to them. In the case of climate change, I think people are now recognising it as a personal risk. Lots of people are dying in heat waves and tremendous damage is being done in extreme rainstorms that are worsened because of more water in the air because warmer air holds more water. So it's become personal, it's become perceptible. But there's a third 'P' that is part of solving any environmental problem and that is that people have to believe that the solutions are practical. And unfortunately, I think we've been sold somewhat a bill of goods, but also the evolution of this problem has been so fast that it's hard to follow.
Susan - People have believed that there is no practical solution, that there's nothing they can do. There's plenty they can do. We never solve any environmental problem until people get together and demand change. That's one really important thing you can do, even by the simple act of voting. If not, even better, by participating in groups or even just talking to people, talking to your neighbours, talking to people in your church, whatever, wherever you go and and meet people. All of that is really important in terms of personal actions. If you're working and you have investments in your retirement, like a 401(k) as we call it, you can take a good hard look at those investments and try to decide which ones you think are good for the planet and which ones aren't. There are many ways to put pressure on industry to change.
Susan - If you don't mind, I'll just say I've written a book about this where I go through a whole series of environmental problems and I show how important those three P's are in solving every one of them, whether it's lead and gas and paint, or DDT or smog or the ozone layer or climate change. The three P's start us off and then what we need is technology steering. So what I mean by that is that people's demand for change will motivate industries to make changes and it will motivate governments to do things that further foster those changes. Even if what the governments do is something as simple as funding research to investigate what you can use in a spray can instead of a chlorofluorocarbon, or how well you can do with different types of batteries so that you can use solar instead of fossil fuel energy and your power plants. All those kinds of things are happening because people demanded it.
Chris - The one 'P' that people never mention when discussing this though must be the P for population. Every person listening to this programme in a western country has got a carbon footprint of up to 10 tons of carbon dioxide per year. The more of us there are the bigger that's going to be. But no one mentions the fact that were we to have a much smaller human population, it was not growing at the huge rate that it has, we would have a much smaller problem.
Susan - You know, it's so much fun. Every time I talk about the three P's everybody always wants to add a fourth one and it's a lot of fun to think about them. The population issue is an interesting one, though. I take your point that the tremendous growth of population of the 20th century has meant that we have a lot of people on this planet, but we're not projected to grow that much more in the future. We have on the order now of 8 billion. I'm not sure it would've been much better if we'd stopped at 3 but we didn't. We are where we are. We have 8. The real problem today is that there's about a billion and a half, maybe 2 billion people living a comfortable, if you will, developed country lifestyle like what we have in the United States and Britain.
Susan - But there are some 5, maybe 6 billion people out there in the world who really are suffering and don't have electricity, they don't have toilets, they don't have the kind of healthcare we have. That they develop is imperative. I think no feeling person could say that they shouldn't develop, but if they develop using carbon based energy, fossil fuel energy the way we did, the planet is going to get very hot indeed. So I'm arguing that it isn't so much the 20% more people that we're going to have, it's the development of the people that we already have, who right now are emitting per person, I believe the correct number is about 5 times less per capita on average than we do. So you can run the maths on that and what you see is that if they use fossil fuel energy, that's what's going to cause it to balloon.
But they're already here. It's not so much a future population. You're right that perhaps we shouldn't have let it get to this point, but why did it get to this point? Well, partly it got to this point because we got so much better at growing crops and so we could feed people more easily. We developed fertilisers, we developed vaccines and healthcare that even though it's not complete, it at least does something about some of the worst childhood diseases. So survival rates are better. I guess I don't know how you can be against any of that. What we need to do is learn how to exist on this planet sustainably, all of us.
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