 Thank you so much for being here today for this NCAR Explorer Series Conversations Event, streaming live from our homes to yours. My name is Dr. Dan Zietlow, and I work in education and outreach here at the National Center for Atmospheric Research or NCAR, which is a world-leading organization dedicated to understanding our system science. And that includes our atmosphere, our weather, climate, the sun, and how all of these systems impact our society. We've got a really great event planned for today with Dr. Michael Mills, joining us from the Atmospheric Chemistry Observations and Modeling Lab, or simply ACOM. And we're going to chat all about volcanoes, especially volcanic eruptions and how those eruptions can actually impact our global climate. And this is definitely a timely topic, not only because today actually is 41 years since the 1980 eruption of Mount St. Helens, but we're also hearing a lot about volcanic activity all over the world, including Iceland, as well as the recent eruption of last week, the area that's really impacted St. Considium and Grenadines. So throughout this event, you can ask Dr. Mills questions and engage with us through interactive polls using Slido. So if you scroll down this webpage just a little bit, right below where you see the video of this webcast, you can actually join Slido and answer some of the polls we currently have available, particularly the word cloud on what you think of when you hear the word volcano, because we're going to get to that pretty soon. I also just want to quickly note that this conversation is being recorded and we will share it out through our NCAR Explorer Series website. Now, before we check in and see your thoughts on our word cloud, let's meet Dr. Michael Mills. So Mike, can you tell us a little bit about yourself and what you do here at NCAR? Hi Dan, thanks for that. I, as you said, work in atmospheric chemistry and I work on global climate models that have a lot of chemistry that affects everything from the Earth's surface all the way up to the edge of space. Specifically, I do modeling of processes that follow volcanic eruptions that affect our stratosphere and the ozone layer and the climate. I've also done research on some related issues like nuclear winter and how particles from smokes after a nuclear war could lead to effects on our climate as well as things like geoengineering. That's awesome. And that's one of the neat things I've noticed about a lot of stuff that you do is there's so many different applications even though it's kind of broadly under the umbrella of, you know, how does our atmosphere impact global climate? Yeah, it's in it. Largely my work is at the interface of particles suspended in the atmosphere and the Earth's system. Awesome. Well, before we go any further because I know we have lots to talk about today, let's go ahead and take a look at the responses to our work cloud. So Paul and Aliyah, would you be able to share that work cloud for us? All right, so it looks like the demo one answer that our audience thinks about when they hear the word volcano is blada, which I think is totally fair. I also am seeing eruptions, fire, atmosphere, geology, red lot of smoke, Mount Vesuvius, volcano, beauty, power, danger, aerosols, my youngest daughter. I'd be curious to learn more about that one. What else do we have? Explosive Iceland, my job. That's a great one. We must have a volcanologist on board with today. Source of damaging lava flows and sulfur. Cool, so yeah. So hearing all of that from our audience, I'm super curious, Mike, like how did you get interested in what you do? Well, I mean, first of all, who doesn't love a good volcanic eruption? And as you mentioned, on this day in 1980, a little mountain in Southern Washington state erupted called St. Helens. And it basically covered a good part of the Pacific Northwest in ash. And I was 12 years old when that happened. So great age to be really interested in that. But in terms of my professional career, it was later when I was working here in Boulder in graduate school with my PhD advisor, Dr. Susan Solomon, who I'll talk about a bit today. And she had really done a lot of groundbreaking work on ozone loss and the ozone hole over Antarctica. And I was trying to figure out what to do my PhD thesis on when this volcano erupted in the Philippines in June of 1991. And it turned out to be the biggest impact of a volcano on the stratosphere, the biggest amount of sulfur probably in the 20th century. And so it had an effect on our climate. It also had an effect on the ozone layer. And I started working on modeling that in the computer models at that time. And I've been working on things like that ever since. I also wanted to show my first slide here, which is a, let's see, share my screen. This is a beautiful animation of a series of images taken by an astronaut on the International Space Station in June 12th, 2009. This is Serachev Peak on an island in the Coral Islands between Russia and Japan. And you can see all sorts of things going on here. All that gray stuff is the ash that you think about with Mount St. Helens. There is some lava action going on down the flanks of the volcano. That's called a pyroclastic flow. There's some water vapor condensing in the cloud there as well. And this eruption was important as well to the climate and the ozone in that it also put sulfur gases into the stratosphere. And as I'll talk about, that has global impacts. That's a really cool invention, I gotta say. That's pretty awesome to see. And I think it goes back to a couple of the things our audience was saying with the work slide. You know that volcanoes are beautiful and they're also kind of dangerous and scary at the same time. Now, I know as we were talking kind of before this event that you have a very interesting story to tell about this summer, or I should say the year that there wasn't actually a summer. So what was up with that? This was early in the 19th century. It was, the year was 1816. It was one year after the Battle of Waterloo. So Europe was recovering from Napoleonic Wars and actually in 1815, the year before the year went out of summer, about the same time as Waterloo was happening, a volcano was erupting all the way around the other side of the world in Indonesia. And it may have been the most explosive volcanic eruption of the last 10,000 years. It's called Mount Tambora. It happened on an island where there were about 12,000 inhabitants of which only 26 survived in surrounding area and other islands, the eruption and earthquake. And there's also tsunamis killed about 90,000 people and all around the area, about 200 miles around the volcano experience about three days of total darkness because of all the material in the atmosphere blocking out the sun's rays. And then on the other side of the world, here we are in Connecticut and New England and the United States, the Northeast. This is a look at the mean June temperatures in Connecticut over the period from 1790 to the year 1860. And we see this outlier here starting in 1816. That's the year without a summer when the mean temperatures really dropped. And again, in 1817, they were still pretty cold. And this is a quote from a great book about the eruption by Gil and Darcy Wood. It's called Tambora, the eruption that changed the world. He says, for three years following Tambora's explosion to be alive almost anywhere in the world meant to be hungry. In New England, 1816 was nicknamed the year without a summer or 1800 and froze to death. Germans called 1817 the year of the beggar. Across the globe, harvest, perish and frost and drought or were washed away by flooding rains. Villagers in Vermont survived on porcupine and boiled nettles while peasants of Yunnan China sucked on white clay. Summer tourists traveling in France mistook beggars crowding the roads for armies on the March. And another interesting story is that this, the same summer there were a group of poets and writers, Percy Shelley and his wife, Mary Wollstonecraft Shelley and their friend Lord Byron, they went to Switzerland for the summer and they had such dismal weather there that they entertained each other by telling ghost stories. And this is how Mary Shelley started ended up writing the book, Frankenstein. So here's another effect of the year without a summer in New England. We see us the snow line in June of 1816. We don't usually have snow in the summer in New England. So it went all the way down to the southern border of Vermont there. So that's pretty severe. And this had a big impact on the ability to grow crops. The growing season was greatly shortened. This is the number of days that you can grow between frosts, it was shorter in 1816 than any other year in the several decades before and after. And as a result, the prices of staple crops really spiked. Wheat and corn went up. On the other hand, a lot of livestock had to be slaughtered to avoid starvation. So in fact, prices of meat fell in many cases. There was famine in Europe and in India. There were riots in France. As I said, Europe was still recovering from the Napoleonic Wars. People started leaving New England. This is the rate of emigration, the number of people leaving Vermont spiking in the year 1816. In fact, Vermont's population growth was set back by seven years and the population went down by 8%. And as people started moving to what they call the West, what we now call the Midwest, it spurred the creation of the Erie Canal which connected the Hudson River to the Great Lakes. And that started in 1817 to improve transportation. We also had the first cholera pandemic following this eruption which started in India in 1817. But this is the first time that cholera spread outside of India. And it's been linked to changes in the monsoon that the subcontinent really relies on for food. In the time when it's normally wet, it was dry. And when the time when it was normally dry, it was wet. And this has been linked to the spread of this disease into a pandemic possibly. I mean, for us at NCAR, one of the things we're always thinking about is the Earth system, right? Like how is everything connected to one another? And this is all just the great examples of how one volcanic eruption can cause all of these things, including writing a book about Frankenstein. It's interesting too, I think. For me, I remember the first time I kind of had this realization of how I can be affected by a volcano, even if I don't live anywhere near one. I was living down in New Zealand at the time, actually, when the big volcanic eruption in Chile happened and it like shut down all the air traffic in the Southern Hemisphere. I mean, just kind of stranded there for a little bit. I was like, oh wow, like we're nowhere near this eruption. And yet it's an emptiness, you know, thousands of kilometers away. Was that in 2015 or 2011? 2011, yeah. Yeah. There were a couple of eruptions in Chile both those years. And my last slide today, I will look at how they both affected the ozone hole in Antarctica. Oh, great. I'll be fun to get to. So I don't see any questions yet. So if you're out there in cyberspace listening, definitely ask questions all throughout. We're gonna be taking them as they come in. So now one thing that we're definitely gonna talk about today is what obviously happens after a volcanic eruption. So we have this eruption that happens. There's all this particulate matter and gases spewing out. So how does that then interact with our atmosphere and how can that then actually change our global climate? Oh, I'm glad you asked. I have this little cartoon, animated cartoon from the New York Times, which illustrates some of the processes and simplified form here. We talked about the ash that comes out of a volcano, but the ash actually doesn't last very long in the atmosphere. It doesn't get very high and it's pretty heavy and dense. Tends to fall out or get rained out within a few weeks at longest. But there's another component of volcanic eruptions that can affect the climate for several years. And usually that is a gas called sulfur dioxide, which if it gets high enough in the atmosphere, it is immune to rain out. It gets into the stratosphere. And we'll talk about that later. But this gas then reacts and it forms little tiny and shiny particles of sulfuric acid and water, which can grow. And these particles can stay up in the stratosphere for three years, sometimes longer. And while they're up there, they're reflecting sunlight back into space so that sunlight doesn't get to the surface. And that results in the surface of the earth being cooler for a few years after eruptions like that. And this is a little bit more detail in what I'm talking about, where we have the sun on the upper left and it's putting out the sunlight in the visible and in the ultraviolet. That's what we call shortwave radiation. And those wavelengths get reflected back out into space as well as some of it gets scattered. And so often after a big eruption, you can see really beautiful sunsets of striking colors as well. And there are other effects of these particles, which we call aerosols, aerosol particles are the little tiny, shiny droplets that are suspended in the air. And among them is they can absorb some of the earth's heat as it's escaping into space. And that doesn't generally warm the surface, but it can heat up things in the stratosphere. So this is some of the chemical processes we're talking about. There's a two gas coming out of the volcano and following these chemical reactions to form this H2SO4, which is sulfuric acid gas. And then it gets together with water molecules in the atmosphere to form these particles in what we call nucleation or gas to particle conversion. And then that attracts more water and sulfuric acid molecules and they grow by what's called condensation. They can also run into each other and collide with coagulation. And then when they get big enough, they start falling through the air and getting removed. And these are the processes that we include in our, or you see on the bottom, the whole atmosphere community climate model or WACM, which is this model I talked about earlier, which includes chemical processes all the way from the surface of the earth up to the edge of space. That's pretty cool. Yeah, and for everybody, we're gonna talk a little bit more about kind of models and how we use them a little bit later. So again, we're waiting for a couple more questions to come in. So maybe we'll kind of move on to the next topic as we let some more questions come in. But there are heaps of volcanoes all over the world. We got up and down the West coast of the Americas to Alaska, Japan. So all these volcanoes are gonna be behaving differently. They all are gonna have different compositions in their eruptions when they erupt. So what are some of the ways that scientists can actually study all these different volcanoes and the different components of it? And then how specifically do you study the volcanoes for your own work? Well, we have a lot of tools now for observing the effects of volcanic eruptions. And satellites are a big part of that because they're always up in space looking down on the earth. We have good satellites that can measure the sulfur dioxide SO2 gas emitted by eruptions. And here's an observation from Mount Pinatubo, not of the gas, but of the actual aerosol from Mount Pinatubo and in the upper left, we see what's called the non-volcanic stratospheric aerosol layer, which is created by things other than volcanic eruptions. But then in the upper right, when Pinatubo erupts in the Philippines, it starts spreading throughout the tropics as the winds in the stratosphere take it around the earth. And then in the months following in the lower left, we see it starting to spread from the tropics towards the poles. And this is just the circulation of the earth stratosphere moving the aerosols until the entire globe gets covered in a layer of sulfate that's reflecting aerosol back into space seen in the lower right, which is about a year and a half after this eruption in the Philippines. But there are other ways that people measure volcanic effects. One way is to shoot a laser beam that's pulsed from the ground and measure the reflection of light coming back, that's called lidar. And that's a highly precise way of measuring where particles are in the atmosphere. You can get their altitude really accurately because we know the speed of light so well. And we even have satellites that have laser beams shooting down and doing the same thing. But what I do is not to observe these things but to put them into a climate model, which includes, it's a collaboration over decades of our community of atmospheric scientists and earth system scientists because this model is connected to not just the atmosphere but it also has an ocean model, a land model, even sea ice and land ice. And my small role in this model, one of them is to put the processes that convert volcanic eruptions into these aerosols and how they affect the radiation, the climate and also the interactions with the chemistry that affect the earth's ozone layer. So this is a simulation from the whole atmosphere community climate model or WACM of the Mount Pinatubo eruption in June 15th, 1991. There you see it spreading out in the tropics and then it's followed two months later by this eruption in Southern Chile, which puts some stuff in, but now you're starting to see it spreading out from the tropics into the poles. And as it's doing that, this is a measure of the total amount of particles in the stratosphere, it starts thinning out and getting removed in the years, the months and years following the eruption. We're still just a little over a year after the eruption here, but we have a definitely an aerosol covered planet. And in fact, many of us who were around then remember the beautiful sunsets that we saw. And in fact, the following year, I was very lucky that my PhD advisor Susan Solomon sent me down to Antarctica and I got to measure some of the impacts that this eruption was still having on the ozone layer there. That was another animation, just showing some smaller volcanic eruptions. And here's one in 2008 that happened off of Alaska. And we see it doesn't move down to the tropics because of the circulation in the atmosphere. When an eruption happens near the pole, it tends to stay in that hemisphere. Whereas here in 2011, we have three different eruptions happening at three different latitudes and spreading things around. Here's another one in the tropics in 2014 and it starts spreading mostly to the southern hemisphere. And then finally in 2015, there's this Kalbuco eruption in Chile, which is pretty far south in the southern hemisphere. And this has been linked to the, that year there was a record large ozone hole over Antarctica. And it's really not the fault of the volcano, but it's the interaction of these particles with the chlorine that we've pumped up into the stratosphere from man-made sources. And we'll talk about that a bit later in the talk. Cool. So here we're looking at kind of small to moderate eruptions. One of the questions that I see in the chat right now, and actually one question I get a lot as a geologist from friends of mine is about the Yellowstone Supervolcano. So Ian is wondering, how significant is or was the Yellowstone Supervolcano? I'm gonna interpret that maybe as like, if and when the Yellowstone Supervolcano explodes, like how significant of an impact is that gonna have on our atmosphere and global climate? The Yellowstone is, as the person said, a supervolcano that is what we call a hot spot underneath in the Earth's mantle, which punches through the crust. And it's been moving over millions of years as the North America's actually been moving over it. So it used to be out towards the Pacific Ocean and North America has been moving westward and now it's in Wyoming. And over that period of millions of years, it's erupted several times, but the last one was hundreds of thousands of years ago. And I think it's erupted about three times and those were truly catastrophic events. And if something of that size were to happen, now it would produce a very dramatic cooling, much like a perhaps a global thermonuclear war, putting a bunch of smoke up into the atmosphere. And so when you're trying to answer a question like that, first of all, have to rely on indirect observations because nobody was around when those eruptions happened. So we have to look at what happened to life on Earth. And we have proxies of temperature in tree rings and also ice cores and other measures. And when we're building a computer model to simulate volcanic eruptions, we can't be sure that they're going to get everything right because we don't have the same kinds of observations for an eruption of that size. But we're pretty sure it would lead to probably freezing temperatures every month of the year for several years and throughout the globe. And that could wipe out humanity and a good portion of life on Earth. And I'm not happy now, let's take the next question. So there's a couple of great questions in here that maybe we'll get to a little bit later because we're going to talk a little bit more about the gases that are kind of being erupted and circulating. But Mark is wondering, did people understand at the time of the 1816 eruption that the cooling and lack of sunlight was due to a volcanic eruption? That's a great question, thanks. They did not, in fact. In fact, that was in 1815 and 1816 was the cooling. That was well before we had global communications. But there was a much more famous eruption that happened in 1883 called Krakatau or Krakatoa. And that was perhaps the first global news event because it happened after telegraph wires had been strung around the world. And so people knew that an eruption had happened in Indonesia. But back in 1815, 1816, people had no idea why they were freezing together in New England and Europe. Yeah, which is always interesting when you don't really have those observations to put two and two together. Cool, so we'll take one more question because this is also related to the 1816 eruption and then we'll kind of move on. But Chris is wondering, as compared to the eruption in the 1816, what was the comparative power of the eruption of the Lagerida caldera in Colorado and what were its worldwide effects? Well, that's a great question. So as I mentioned, the Tambora eruption in 1815 was perhaps the most explosive of the last 10,000 years. Lagerida happened well before that a few hundred thousand years ago in Colorado. You can go to the Wheeler Geologic Area in Colorado if you're willing to hike it in or you've got a good four-wheel drive. And it's really an amazing, just formation of rock that's made out of the ash from this volcano and it all looks like dribble castles because there was a huge layer of ash that covered a wide area. And so that was an even bigger eruption and we can't be sure of how much sulfur was in it. Some volcanoes put out a lot of ash without putting out sulfur like Mount St. Helens, although Mount St. Helens caused a lot of damage in the US because of the ash. It didn't have very much sulfur to affect the global climate. But if we go back for the last several hundred thousand years, we do have some measurements from ice cores drilling down a mile or two through the ice in Antarctica and Greenland. And we can actually measure sulfur spikes in the gas bubbles that are trapped in the layers of ice that get put down each year there to give us some measure. So I know that Lagarita had a lot more energy than Tambora or anything we've seen in the last few thousand years. I don't know exactly how much impact it had on the climate and for how long because we don't have measurements of the sulfur from back then. That's great. Thanks for all that info. So moving into kind of the next part of our conversation, we do have, I just want to note for the audience, we do have a poll question coming up. So if you haven't answered that quite yet, definitely head into Slido to answer the poll question about since the 1800s, which component of volcanic eruptions has had the largest impact on global temperatures. And we'll check on that just in a little bit. But earlier we were talking about how volcanic eruptions, obviously affect the global climate and specifically how they can cool temperatures. So from some of the work that you've been doing, what are some of the things that you are seeing about how surface temperatures are changing after a volcanic eruption? So let me just show this. This is a figure that we published a few years ago from our simulations using the WACM model I mentioned. And what this shows, if you just look at the black line here, this is what we call the forcing or how the volcano has decreased the amount of energy coming to the surface. These are volcanoes from 1980 till 2015. And so where this black line is dipping down, it's due to reduction in sunlight coming to the surface. And what happened in 1982 is this volcano erupted in Mexico called El Chichon. And that was in the tropics and it did spread some to the Southern Hemisphere. It had a bigger effect than the Northern Hemisphere. And then as I mentioned, 1991, we had Mount Pitatubo decreasing and these calculations in our model are validated from satellite observations which show the amount of energy going into and out of the Earth's atmosphere. And then after Mount Pitatubo erupted in the late 1990s, we have what we call a quiescent period when there weren't very many volcanic eruptions. There were a few small ones but they didn't have a big effect on the Earth's temperature. But since the year 2005, we've had a series of small to moderate magnitude inputs of sulfur dioxide into the stratosphere from eruptions. And it's had some impact on the rate of warming. It slowed that down. In fact, using this model, we're able to compare the small forcing in the late 1990s and early 2000s from volcanoes to the forcing since, well, 2005 to 2015. And the numbers here just show we had three times as much cooling in that decade than we did in the late 90s from volcanoes. And if you compare that to the warming from carbon dioxide over the same periods, these eruptions offset about 30% of the warming over that period. And so they did, in fact, slow down global warming slightly. And that's shown in the next slide as well where the gray shaded area is a range of observations of the global average surface temperature where we've removed the effects of El Nino, which has a big effect and did the same thing with the different models. Now, the green model is one that doesn't include these recent eruptions since 2005. And it shows a bit too much warming compared to the observations. Whereas the black and the blue lines are calculations that include these eruptions and those do better in matching the observations and show that there was a slight reduction in global average temperature. It's only less than a 10th of a degree Celsius, but it was a significant offsetting of global warming. Yeah, it's super interesting. And again, just going back to that, how everything within the earth system is gonna impact something else within that earth system. So let's maybe check out that poll question. So Mike, if you go ahead and unshare your screen, so that way Paul and Aliyah can share theirs. So if we pop that poll question up, since the 1800s, which component of volcanic eruptions has had the largest impact on global temperatures? And our audience seems to overwhelmingly think sulfur dioxide. So Mike, could you give us a little more background on that? Yeah, a lot of people were paying attention. When we came up with this question, I asked to put in since the 1800s because there are different components to volcanic eruptions and they have effects on temperatures on different time scales. Sulfur dioxide, as I mentioned, leads to these aerosol particles that can cool the planet for three to five years. But if we're talking about into the deep past, what we call that paleoclimate, volcanoes over long time scales have been historically significant in affecting the amount of carbon dioxide in the atmosphere very slowly over millions of years. And there've been periods in the deep past over a billion years ago when the earth was very cold and volcanic eruptions may have been part of warming the earth up to get us out of those conditions over a long period of time. But there's certainly a very slow process in changing carbon dioxide, and especially compared to what humans are producing from fossil fuel burning and industrial activity. Great, so there's a couple related questions that I see in the chat right now. Someone is wondering if sulfate aerosols are cooling the planet. Could we actually use the sulfate aerosols to help cool the earth and reduce global warming? This is an idea some people have had. And it has different names. The most frequently used is geoengineering. It's also called solar radiation management. And it's certainly a disturbing concept that we have messed up the earth's climate so badly that we're at a point where we need to mess it up some more in order to offset what we've done. And the problem is that putting sulfur into the stratosphere, as I said, it only lasts three to five years. When you're putting carbon dioxide in the atmosphere, so about 50% of it goes into the ocean right away. And then a good portion of it will be removed over the next few centuries, but about 20% of it will still be there tens of thousands of years later. And so we're talking about geologic time scales and the carbon dioxide unless we can stop emitting it and perhaps we might even have to eventually figure out a way to pull it out of the atmosphere, which is gonna be very challenging. Then putting in particles is only a temporary solution. Now, some people say it could slow down the rate of change and allow adaptation and alleviate some suffering while you're working on technologies that would be carbon-free or that could actually remove carbon dioxide from the air. And that's a serious thing. I have worked on this issue and I went to a conference on climate engineering in Berlin and I actually met a woman from Bangladesh and she said to me that they're interested in geoengineering because even at the most ambitious target we have of keeping warming below one and a half or two degrees of Celsius that very populated parts of her country Bangladesh are gonna be underwater. And so this is thought of sometimes as something that needs to be researched as break glass in case of emergency type of situation. Yeah, there's definitely like you said a lot of research out there still and there's also some ethical questions we have to be asking ourselves as we kind of dive more into the area of geoengineering. Great, so there's a couple of questions related to what we're about to talk about next. So maybe let's talk a little bit about this before we take those questions. So one thing that we set up at the beginning here is that volcanic eruptions have an effect on stratospheric ozone. We just wanna distinguish between stratospheric ozone versus surface level ozone. And so what effect do volcanoes have on the stratospheric ozone and why should we care about that? Okay, so this is a little cartoon showing the different layers of the atmosphere. And down to the surface where we are is what we call the troposphere. And this is an area that's very unstable. You probably know that as you go up higher in altitude the atmosphere gets colder. That happens throughout the troposphere and if you have warm air below cold air oftentimes you get weather, air rising and there's also a lot more to it than that. But as you go up high enough you get to a point where the temperature of the atmosphere starts rising. That's shown by this red line. It's a graph where we have temperature on the horizontal and altitude on the vertical. So we see cooling up to the top of the troposphere to this boundary we call the tropopause. And then we get into what's called the stratosphere where it starts warming. And why is it warming? It's warming because we have this molecule called ozone in greater abundance up there than we do down here. It's formed by oxygen molecules breaking up from very high energy sunlight, ultraviolet light. And that reforms the oxygen atoms reform into a molecule with three oxygen atoms when they collide with an O2 molecule. And that molecule absorbs other wavelengths of ultraviolet light from the sun. And that helps to protect us and shield us from that radiation, which would otherwise be damaging to us because we evolved in a planet with an ozone layer. So we didn't have to worry about the damaging effect of that radiation. And there's a really great story about the ozone layer and how we first discovered the threats to the ozone layer and how we've really created an environmental success to worry out of that. It goes back to the early 1970s when people were proposing a fleet of stratospheric aircraft. And there was a Dutch scientist named Paul Krutsen who worked in Germany. And he's worked at NCAR here in Boulder all around the world. He started suggesting that some of the emissions from airplanes flying up in the stratosphere could be damaging. And that got scientists thinking about that and other things that could damage the ozone. And Mario Molina was a postdoc at Irvine and his advisor, Sherry Rowland. They in the lab found that these chemicals that had been invented in the 1920s called chlorofluorocarbons and were being used increasingly for all sorts of things. People might know of them as propellants and spray cans. They were also used to refrigerate and in air conditioners. They're used to blow styrofoam. They're used to clean computer ships that they essentially, they didn't break down in the troposphere. But once they got above the ozone layer, they did break down from some of that ultraviolet radiation and released chlorine into the stratosphere. And this leads to catalytic cycles where one molecule with chlorine in it can destroy hundreds of molecules of ozone over and over. There are also other things with bromine in them that have the same effect. And a lot of those are used in fire extinguishers, for example, and they predicted a loss of ozone of just about 1% over several decades. And it would happen very high in the ozone layer. But in 1985, we had a big surprise called the Antarctic Ozone Hole. This was first reported by a guy with the British Antarctic Survey called Joe Farman. And he had been taking measurements down there since about 1959. And starting around 1980, he started noticing that the ozone in certain time of the year, starting in September and then in October, November, the springtime down there was just dropping. And by the middle of the 1980s, by 1984 and 85, about half of the ozone layer over Antarctica was missing all of a sudden. And he'd been down there long enough to know that that wasn't right. But it took him a few years until 1985 to write a paper about it. And one reason was he knew that NASA had satellites measuring the ozone and they weren't reporting anything. Well, after the paper was published, it turned out that these ozone levels were so low that NASA had programmed their software to ignore such levels as being unreasonable. So they still had the data. They didn't throw it out. They went back and they found it and there was. But nobody was looking at it. And I mentioned my PhD advisor, Susan Solomon. She the next year led the National Ozone Expedition down in America and she started thinking about what could be causing this. And she saw these beautiful clouds down there called polar stratosphere clouds, which are clouds of ice up in the stratosphere because this is the coldest place on earth. And she started thinking of chemistry that could be happening on the surfaces that were created by these ice particles and how that interacted with the chlorine that we'd been pumping up into the stratosphere for decades and came up with a theory and wrote a paper about it and her expedition and two others basically corroborated this theory and showed that the chlorofluorocarbons and other related compounds were causing this ozone hole and it could be a big threat in the decades to follow that. So it actually led to a pretty quick action internationally where these substances were banned under the Montreal Protocol and the treaty was amended to make it stronger over time. And now we're starting to see the first signs of healing of the ozone hole. So the recipe for the ozone hole is first of all, you have to have these chlorofluorocarbons that humans are producing and related compounds with bromine. You have to have these cold temperatures that you only get in the stratosphere over Antarctica. And they're so cold, they produce these beautiful polar stratosphere clouds. As you can see, they're iridescent. They're also called mother of pearl clouds. They look like inside of an abalone shell. And finally you have to have sunlight. So this is why it happens in the springtime over Antarctica not in the winter because there's no sunlight in the winter there. So the winter is, their winter is our summer and then the sun comes back in their springtime which is September and October. And bam, it really depletes ozone rapidly each year. And volcanoes have an impact on that. This is from a paper in 1996 where these symbols, little asterisks and diamonds are observations of ozone over Antarctica over time from about 1977 until about 1993. And in that time we had two big eruptions as I mentioned before, El Chichon and Mount Pinatubo and those you can see taking kind of a bite out of the ozone each time. And the lines are different model simulations where the dashed line is one where we don't have any volcanic erupt aerosol changing. And the solid line includes the effects of these eruptions. And that matches the observations pretty well showing that the particles that the volcanoes put up interact to create more of these polar stratosphere clouds and cause more ozone loss. And then finally, this is from a more recent paper we did in 2016. And it shows the effects of volcanoes on ozone over Antarctica at the South Pole as calculated in our WACM model from about 2000 until through 2015. And we see a number of these eruptions having impacts of reducing ozone. And the big ones, as I mentioned from Southern Chile in 2011, this is called Pugewe Cordoncalle and in 2015 the Calbuco eruption contributing to the record large ozone hole in the year 2015. And the reason it's important to be able to calculate things like this is because we wanna know how the ozone hole is responding to our efforts to help it heal by banning these substances. And it's gonna, the ozone hole gets bigger and smaller each year depending on how cold it is, but also depending on things like volcanic eruptions. And so when we can remove the effects of volcanic eruptions, we can start to see a long-term trend. And in fact, this paper here is called the emergence of healing in the Antarctic ozone layer. And we showed that we're seeing the first signs of the ozone hole starting to heal because of this environmental success story of the Montreal Protocol. That's great. So in our last five or so minutes here, we have about seven questions for you, Mike. And one is kind of related to what we're talking about right now from Nachiket. Apologize if I'm not pronouncing your name correctly. But besides the anthropogenic CO2 buildup, and then maybe we just talked about how ozone can change. Do you notice any other chemical changes in stratosphere? Oh yeah, there are a lot of things that affect the stratosphere. And the question mentioned the carbon dioxide. And we think of carbon dioxide as warming the earth. And it does that by trapping heat in the lowest layer of the atmosphere, the troposphere. But it also has an effect higher in the atmosphere where it cools the stratosphere. And so that can have long-term effects. Any molecule that lasts more than a few decades and some of them last centuries and millennia is going to start building up if you're emitting it. Carbon dioxide, as I mentioned, can last thousands of years. There's some, there's a molecule called SF6, which has a global warming potential that actually stays in the atmosphere for tens of thousands of years. And it's a very powerful greenhouse gas. And then things like methane, which come from agriculture and from bacteria fermenting, it can come from rice production, but a big part of it comes from the digestive tracts of animals like cows and sheep. Methane lasts for a few decades and warms the atmosphere. And then once it gets up into the stratosphere, it does break down, but it also produces water up there. And so we're starting to see more water in the upper atmosphere from increasing methane. So there's all sorts of global changes effects on the upper atmosphere. Great, and maybe building on that, this may be a quick question. Ty's wondering if there's a big difference between volcanic aerosols staying contained in the northern hemisphere versus the southern hemisphere. Well, there are a lot more people in the northern hemisphere and there's a lot more land in the northern hemisphere. And so more people and food production is affected by eruptions in the northern hemisphere. And then as we saw in the southern hemisphere, because that's where the IR goes own hole is, eruptions that happen in the south have a much bigger effect on that. There are different reasons why there's a lot bigger ozone hole over Antarctica and not so much of an ozone hole over the Arctic, having to do largely with where the continents are and how the winds shape up there. So yeah, there are a lot of different hemispheric differences. Great, and now our next question is the highest voted question right now. And it's for all of our students that are out there now. So a high school student is wondering, what should I study for a job like yours? Yeah, well, a lot of math and physics. I do do chemistry, but I never really took a lot of the nasty organic chemistry, but I don't really understand. So the chemistry is more simple to most scientists, the chemistry that I do. But if you're interested in looking at pollution in the troposphere, then certainly organic chemistry is very important. We have all sorts of volatile organic compounds coming from not just pollution, but also from vegetation. And if you're considering a career in this field, I just say it's important to really talk to as many people who are in the field as possible and get a sense of what they do and what you'd like to do. Yeah, thanks for that advice. And definitely reach out to us too. We like to talk. So if you have questions, reach out to us. Great, so maybe in our last couple of minutes, we have about five questions. So they can be like quick fire answers, which I think might work with the remaining ones. So the one I'm seeing right now is what is the most dangerous volcano in the US or world? Yeah, probably Yellowstone. Great, and then next question. Michael's wondering, what is the relationship between volcanic areas and then earthquake prone areas? So a lot of times earthquakes will be measured before there's an eruption because there's lava moving underneath the volcano. And so that can be used sometimes to predict a volcanic eruption, but not always, sometimes there are surprises. And then a lot of the big earthquakes are not necessarily related to volcanoes, they're just due to fault lines slipping and that can happen on continents and also in the middle of the ocean and create tsunamis. And then maybe a follow on question to that, are volcanoes simply a spot where the earth liquid mantle comes through the crust? So that's a great question. I mentioned that happens in Yellowstone, that's a hot spot. Another example of that is Hawaii where we have a chain of islands and there's really only one of them over the hot spot, the big island Hawaii, but all the other Hawaiian islands used to be over the hot spot and they moved and they're smaller than the big island because they've eroded over millions of years since they've moved away. But most volcanoes are not from something like a hot spot, they're due to plates getting subducted in the, for example, in the Northwestern US, there's the Pacific plate going underneath the North American plate and things like water get trapped in there and as they get heated up in the mantle that water turns into gas and that wants to create an explosion and lava can find its way to the surface through that sort of geologic process. Great, and maybe staying on the theme of the Yellowstone super volcano, Michael's wondering if one, is there a range of scenarios for different eruption energies? And two, will global cooling have severely dimmed sunlight as well? There's a scale called a volcanic explosivity index which is a logarithmic scale where you go from one to two, you're about 10 times more energy or something like that. And I think it goes up to six. So scientists measure volcanoes on a scale. Actually, I think there are more energies and failure eruptions than that. And so the energy is one factor. It's not necessarily the most important factor in how it'll affect the climate. It can determine whether material gets high enough into the stratosphere that has a global effect. But you also need to have a sulfur in order to have a lasting impact. And the, yeah, I guess that's my answer. Yeah, it's great. Great, so our last question and this is kind of a fun one because as earth scientists, we love our acronyms. Katherine is wondering, I've always wanted to know how did the name Wacom come to be? Yeah, I wasn't there at the time but there are the three scientists really who the fathers of Wacom who work at NCAR and they, I don't know, but it's a great name. And we have fun with it, especially when we're trying to tune different parts of the atmosphere so that they match what we see. And when we fix one area and another part goes out of Wac, and we call that Wacomole. Perfect, I love it. And with that, thank you, Mike, so much for being here today and kind of sharing all your knowledge about volcanoes and the work that you do. Thanks very much. Yeah, and I also just want to give a quick shout out to our team behind the scenes. So Paul, Brett, Alia and Lorena, thanks for helping things go smoothly at the background. And for everybody, if you're interested in more NCAR Explorer series events, definitely check out our website for all of our upcoming lectures and conversations and also to view recordings of our past events. And so I hope to see y'all next time and have a great rest of your day.