Ideas - The natural — and unnatural — history of air on Earth

Episode Date: September 25, 2025

Air is one of the most essential elements for human life. Yet even though we depend on air, we humans are dramatically changing the atmosphere — making the air unbearably hot in some parts of the world, unbreathable in the most polluted parts of the world, and pushing the climate toward tipping points. As humans who caused this, we have to adapt to ways we’ve altered our air.

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Sweeltering heat mixed with drought has left much of the country scorched and tinder dry. From Toronto to the nation's capital, Quebec City and Niagara Falls. Heavy smoke from western wildfires clogged the air. The rising temperatures broke more than 60 records across Canada. Across the Mediterranean, from Portugal to Italy, Turkey to Montenegro, wildfires are burning. A heat wave gripping southern Europe has seen temperatures soaring up to 43 degrees Celsius. Normally, you could easily go through a day without once thinking about the air you breathe. But across the country and around the northern hemisphere, we've been very aware of the air.

How smoky it is, how smelly it is, how hot and sticky it is. If you can see the air, something as bad is probably happening around you. My name is Sam Keen. I am the author of six books, including the disappearing spoon and Caesar's Last Breath. You should not be able to see or smell the air. That's bad news. Of the four classical elements, air, earth, water, and fire, air is the one we depend on most. It is strange in that the air around you is the most important thing that surrounds.

you right now, and yet we hardly ever think about it unless something does go wrong. So, you know, you can get by without solid, like, food for a couple weeks, without liquids. You can get by, you know, a day or two, and you'll pull through that. Without the air around you, you wouldn't last more than five or ten minutes. You'd be dead. You need air around you constantly all the time, but we never think about it. We just sort of take it for granted that it's there. And it pretty much always has been there. really important for pretty much every stage of Earth, especially life on Earth. I think of the story of the Earth as a story of gases because you can really retell the entire history of the world by looking at its atmosphere. In fact, every time we take a breath, we essentially inhale the

entire history of Earth each time. It's a four and a half billion year history of massive changes to the character and composition of the atmosphere, sometimes life-giving, sometimes poisonous, sometimes dangerously hot, sometimes frigid, and sometimes, like for the past 10,000 years or so, just right, at least for human civilization. The difference now in the Anthropocene is that it's not the earth that's causing that change,

it's us. And now we have to deal with and adapt to the ways we've altered. our air. Here's a natural and unnatural history and possible futures of our air by Ideas producer Chris Watskow. Everyone has always known that we're breathing, but as to the fact that we're actually breathing something that has substance, that was really quite recent and particularly

the kind of people who looked at it and thought, that might be made up of things. It might be heavy. It might be substance in its own right. I'd say that the first person to understand that air was actually a kind of heavy thing was actually Tori Shelley, who was a disciple of Galileo. I'm Dr. Gabriel Walker. I'm a climate scientist, broadcaster, writer, and I'm currently co-founder of curate and rethinking removals, two organisations dedicated to trying to grow the solution of carbon removals to take CO2 back out of the sky and keep it at. Tori Shelley is the first person to measure and weigh air. When he figured out that air is actually something that has substance, it's a real thing, he wrote a letter to one of his friends. He said, we live submersed at the bottom of an ocean of air. I was fascinated by that because it made me realize that we're like lobsters.

We're walking around like on the surface of the sea and we're not understanding that there's an entire ocean of things that are happening above us currents. and animals and shifting things that are happening above our heads. And Torricelli is the first person to realize that. Earth has had four distinct atmospheres in its history. So the very first atmosphere we had came with the planet when it was just forming. It was a very thin atmosphere, I call it sort of a comb over atmosphere, very wispy. And essentially, it was left over hydrogen and helium from when, the Earth was forming in the first place. So very thin, and most of that got blown away

pretty quickly into outer space, and we lost that first atmosphere. The second atmosphere essentially came from the ground. So early Earth was a hot, dynamic place, a lot of volcanic fissures, volcanoes, vents where things were leaking from the ground. And essentially, there were a bunch of dissolved gases inside the earth itself, beneath the crust. So it's sort of like the bubbles in champagne. You open it, the gases rush out. The same thing was happening with these volcanic vents and fissures. And a lot of these were pretty nasty, horrible gases.

You had some that were fairly benign, you know, carbon dioxide, water vapor. But you also had things like hydrogen sulfide, or you had sulfur dioxide, ammonia, stuff that if you were to go back to that time, you know, get out of a time machine or something and step outside and try to take a deep breath of air, your lungs would start burning. It would destroy your lungs. These are very reactive gases, and you would not survive very long on this earth. In fact, life probably would have been impossible on this earth with those gases. At the very beginning, the earth was extremely hot. That's Stephen Earl, an earth scientist who's taught at Vancouver Island University in Nanaimo

and Thompson Rivers University in Kamloops. And in books like a brief history of Earth's climate, he chronicles climate changes from the deep past that played out like slow-motion disaster movies. The surface was probably too hot for water to exist, so it would have been water vapor in the atmosphere. After that, it cooled enough for water to condense, and that's when life was able to get started.

but it was still a warmer atmosphere that was very alien to the earth we know now. So it was rich in carbon dioxide, much higher levels than now, and then methane levels started to increase because methane-producing organism started making more methane in the atmosphere. And then, by about two billion years ago... Then the third atmosphere we had was a very slow building, atmosphere. So these gases, the volcanic ones, were very reactive, and they would react with each other, they would react with rocks, minerals, things like that, and they would disappear from the air.

Meanwhile, though, there was a tiny bit of nitrogen that would get released in the volcanic vents in fissures, probably less than 1%. But the thing about nitrogen is, it's very unreactive. There are three strong triple bonds between the two nitrogen molecules, and it's very hard to break those. It's one of the strongest bonds in all of nature. And so when this nitrogen would leak out and get into the air, even though it was a very small percentage of each individual eruption, overall, it's built up over time and eventually became the dominant gas in our atmosphere. So the third atmosphere was the rise of nitrogen, and it really made for a much more benign, safe atmosphere for life. It was like a nice blanket over the earth, a protective blanket, as compared to the horrible reactive gases that had preceded it. And then the fourth atmosphere is the one that we know

today. So the fourth atmosphere involved the rise of oxygen from cyanobacteria at the start. In other words, algae. And it's a byproduct of photosynthesis. So when cyanobacteria figured out how to photosynthesize to essentially turn carbon dioxide and water into sugar molecules into glucose, oxygen was a byproduct of that. They would release the oxygen as a waste product. And so once photosynthesis started happening, the oxygen level started to go up. But it didn't go up quickly at all because there were so many places where that oxygen

could go into chemical reactions and into decay of organic matter and so on. So it took quite a long time for the oxygen level to become significant, in fact, a very long time, a couple of billion years. Nowadays, plants and other microbes produce most of the oxygen. And after nitrogen, oxygen is the next biggest element in terms of its constituency in the atmosphere. So we have roughly 79% nitrogen and 21% oxygen. That's what we have in the atmosphere now. And how unusual is it to have a planet with an atmosphere with so much oxygen in it? I can say it's really rare. If we look at the planets and the solar system, every planet's got a strange atmosphere anyway, and we look at the planets we've been discovering outside the solar system. But oxygen is extremely reactive. And so it's actually quite hard to keep it in the atmosphere. And if you have too much of it, you just get rampant burning. of anything that's around.

But it's also, it's actually quite poisonous. And that's an interesting thing because we think of oxygen as the thing that keeps us alive, and so it is. If you were to describe it in the jargon of the tech business, oxygen is a highly disruptive molecule, creative destruction on a geological scale. Oxygen essentially nearly wiped out life on Earth,

which is kind of a startling thing to hear nowadays because we associate oxygen with breathing, but for most of life throughout Earth's history, oxygen was a deadly, terrible poison. Geologists, in fact, refer to what they call the oxygen catastrophe. This was before multicellular life, so it was all single-celled life at the time, but it nearly wiped out life on Earth before it really got going. The thing about oxygen is it's very reactive. It goes after pretty much anything.

It tears off the bonds between other atoms and molecules. it's really a destructive kind of nasty gas in some ways. It's a massive die-off, like a big pollution episode in the atmosphere. And they had to bury into places where the oxygen couldn't get to. They had to bury it into marshlands and sort of deep under layers and layers of mud. And indeed, there's the same kind of bacteria. They're bacteria that make methane. They're the same bacteria that exist in our gut and why we fart.

And they're doing that. They're burying themselves in our gut so that they can get away from that horrible point. poisonous oxygen. And it would be the equivalent nowadays if there were a bunch of chlorine gas or something like that in our air and we were trying to breathe it. That is the situation that these microbes face. So you might say, in that case, if it's poisonous, why can we breathe it? Why do we need it to live?

And the answer, I think, is fascinating, that oxygen is like rocket fuel. It's the thing that we needed to get big. So without oxygen, all life on Earth would only be the size of a pinhead. It would still be those tiny single-cell bacteria. You cannot have a large animal or organism of any kind that doesn't have some kind of oxygen metabolizing process going on. So it allowed for animals to start getting large, and that started happening around six, seven hundred million years ago. And what they do with oxygen, essentially, is they treat it sort of like plutonium in a nuclear power plant, because plutonium is very powerful. It can get a lot of energy.

out of it, but you have to keep a very close watch on the plutonium, and you have to sort of keep it confined in certain safe spaces. That's essentially how our cells treat oxygen. You don't want rogue oxygen going around in our cells. It's the mitochondria in our cells that do this, that handle oxygen. And those mitochondria were once free-roaming bacteria on their own, and they are the ones that figured out how to harness oxygen and use it in a safe manner. So if they had not been able to do this, life as we know it would not exist because we wouldn't have multicellular life. So I guess then if you looked beyond Earth, you know, we look to other planets, exoplanets, and we think, oh, it has an oxygen-rich atmosphere. It must be hospitable to life. But that's not a given, is it?

Yeah, you're right. It's not a given that just because you find oxygen, you are going to have life there. In fact, that could be possibly a sign of extinction on that planet. So it really goes both ways with oxygen. It could be the sign of something very exciting happening there, or it could be the sign of things gone very wrong. Oxygen is a thing that fuels us furiously so that we can be big, multi-celled animals that do all the crazy, inventive things that we do.

But it's also killing us, because oxygen is the reason that our cells get gradually damaged when we grow old and die. So the thing that makes us able to be big and inventive and creative and multi-celled and all the things that make us human is also the thing that in the end takes it all away from us. I had no idea it was so diabolical an element. I think oxygen is fantastic. It's the absolute essence of the human condition.

Given how reactive oxygen is, how did it stabilize? How did we come to a point where, you know, like we've got, what, close to 20% oxygen in the atmosphere, and it seems to have been that way for quite a while? The levels of oxygen have veered up and down in the past. So it's been as low as, you know, 15% in the past. It's been 35%. Now it's around 21% because there's a decent balance of plants, cyanobacteria, producing it. So it's just that we're sort of in an equilibrium right now.

it could change, and it has changed in the past. Geologists have found evidence of much higher oxygen levels in the past through insects, essentially. Insects have a different breathing system than most other animals do, in that they don't have lungs that take in oxygen, they'll breathe it in the way we do. They have little pores on their skin, and oxygen just sort of passively diffuses into them. We, we can draw a big breath in, and it diffuses in our blood and gets to all of them. our interior cells. That's harder for an insect to do because the passive action of bringing oxygen in that way just can't diffuse as far into their cells. That's why they're usually very,

very tiny. But in the past, when oxygen levels were something like 35%, you had much, much bigger insects. Geologists have found spiders that were the size of, you know, like pizzas, there were dragonflies, the size of seagulls, there were millipedes, centipedes, a yard long. So when oxygen levels are much higher, insects can do some pretty unusual things. So the makeup of our atmosphere has undergone some enormous shifts over four and a half billion years. And along with that, huge, literally life-altering changes to the climate. Greenhouse gas levels are really what matter here. When we started out, carbon dioxide levels were really high.

The earth was probably quite consistently warm. But over time, different gases in the atmosphere, they're concentrated. have changed quite significantly, and that has allowed for different types of life to evolve. So the three main greenhouse gases in the atmosphere are carbon dioxide, the famous one, and then methane, natural gas, and then nitrous oxide, which is something that comes from fields, in particular when you use fertilizer, and then the fertilizer is oxidized. So all three of them are extremely good at trapping heat. So what they do is, it's called a greenhouse effect, but it's a bit more like a blanket. If it's cold outside and you put a blanket on, the blanket traps the heat

that comes from your body and doesn't let it go outside, and therefore you get warmer and warmer, even though the temperature of the room doesn't change. And in a way, that's what happens with the greenhouse effect. The greenhouse effect is a little bit difficult, and you have to understand some fundamental things. One of them is that everything vibrates. Big things vibrate slowly, small things vibrate very quickly. And gas molecules in the atmosphere are also objects that vibrate and they vibrate in different ways. Several of them that have more than two atoms, like carbon dioxide, methane, water, nitrous oxide, vibrate in such a way that they absorb infrared radiation that is emitted by the warm surfaces of the earth. That infrared radiation typically

it goes right out into space, unless it gets absorbed by greenhouse gases. If I understand this correctly, what happens is the strongest greenhouse gases, like methane, carbon dioxide, nitrous oxide, and that sort of thing, they happen to vibrate at the same frequency as infrared light, and that creates heat that they store in the atmosphere. That's correct, yeah. So they have bending vibrations, which are slower than other types of molecule vibrations, and those are the ones that are at the same frequency as infrared radiation. And when the infrared radiation hits those molecules, it makes them vibrate more vigorously, and that warms them up, and that energy, instead of going out into space, is held within the atmosphere. We need the greenhouse effect to keep the earth warm enough to be livable, but if the level of greenhouse gases, carbon dioxide, methane, etc., gets too high,

the greenhouse effect becomes too strong and the atmosphere gets too warm. One of the funny things about carbon dioxide is that there's only very small amounts of it in the atmosphere, but it acts like chili powder in a stew. You don't need very much of it to have a very big impact. They punch way above their weight. Carbon dioxide is currently at 420 parts per million in the atmosphere. That's 0.04%. Which, seems ridiculously little and how could that possibly have an effect. But they are very potent at absorbing that infrared radiation. Methane is way lower still, like about two parts per million. 0.0.02%. And yet because it's a very effective absorber of infrared radiation,

it also has a significant effect. Life is what first produced some methane in the atmosphere, started taking CO2 out and emitting methane. And of course, life on Earth is still doing that on a huge scale. Photosynthetic organisms are using carbon dioxide to make leaves, branches, stems, and that is taking it out of the atmosphere. So life is critical. But other processes are really important in terms of greenhouse gas levels. One of them is volcanism.

Another important process is weathering, and most people don't really know what the heck I'm talking about when I say weathering, but when rocks get weathered, they actually consume some carbon dioxide from the atmosphere, and so they pull that down. And over longer geological time periods, like hundreds of millions of years, which is the sort of time it takes to build a mountain range, and then for that mountain range to erode away and those rocks to be weathered, there can be a significant change in the carbon dioxide level,

level because of that weathering. And what we do know is over the years, decades, centuries, millennia, and thousands to millions of years, we can trace how carbon dioxide has had a big impact on the atmosphere. And that's one of the features of why we ever got into a snowball earth and why we got out of it. That was Gabriel Walker, the author of an ocean of air and snowball earth. This is Ideas. I'm Nal. what kind of person takes on the law can they ever really know what they're getting into a really tough looking guy came up to us and said are you part of this gay case my family started getting death threats i wasn't able to go outside alone anymore i'm phelan johnson host of see you in court a new podcast about the cases that changed canada and the ordinary people who made history this is david and goliath we have here find and follow see you in court

wherever you get your podcasts. Yes, that's right. Snowball Earth. It seems like the stuff of science fiction. But hundreds of millions of years ago, evidence suggests that the Earth was a completely frozen planet. And we're talking about a mean temperature of around minus 40 degrees, which is enough to freeze the oceans over completely,

probably in many areas with about a kilometre thick of ice on the oceans, and the land would have been glaciated as well. Here's the second part of ideas producer Chris Wadskow's documentary on the natural and unnatural history and potential futures of air on Earth. One of the reasons that scientists think that we could actually have a snowball earth, first of all, is that the continents were in a particularly favorable position. You know, they move around the earth about the pace that your fingernails grow. And they were in a particularly favorable position for the temperature to get colder and colder

and to be soaking up CO2. And the chemical weathering would have increased its pace very strongly, which meant a lot of CO2 drawdown before the snowball earth. And so that's one of the reasons that we got into the snowball earth, but the question is how do we get out of it? So a few things happened roughly 625 million years ago. Most notably, volcanic activity pumping carbon dioxide into the atmosphere, faster than weathering, was pulling it out. Eventually, the icy shell covering the planet began to melt, and evolution could resume its long march toward complex life.

Life at that time was still probably all within the ocean, and the oceans were still there underneath all that ice, and the organism continued to live, maybe not thrive, but they were there, and then when the ice eventually melted, it kind of triggered evolutionary processes that bring us to where we are today. Some of the very earliest complex life forms evolved shortly after snowball Earth. And so you'd have gone from an ice house very rapidly to a hot house. And that happened several times two billion years ago and several times again 600 million years ago. And that's one of the ways that we know that CO2 has this impact on the climate. And understand that every single time that CO2 goes slightly higher in the atmosphere,

then the temperature goes up. And every single time it goes lower in the atmosphere, the temperature goes down. So that the match between CO2 and temperature is very, very strong. And that's what we're seeing spectacularly in the climate change we're experiencing today. And in dramatic heating episodes from long, long ago. 250 million years ago, the end of the Permian, the beginning of the Triassic. In Siberia, there was a volcanic eruption that went on for thousands of years. It's called the Siberian traps.

And the amount of carbon dioxide emitted over thousands of years was enough to significantly warm the atmosphere and resulted in extinction of about 95% of all known organ. So that's massive. And more recently, relatively, 56 million years ago, the Earth experienced something called the Paleocene-Eocene Thermal Maximum. The temperature increased dramatically. And the evidence that we have point to two possible things.

One is volcanism. There was a lot of volcanism going on in the Atlantic Ocean Basin, as North America and Europe we're spreading apart from each other in South America and Africa doing the same thing. So that might have been part of the trigger. And another part of the trigger is Milankovic cycles. Melankovic cycles bring changes to the Earth's axis and the shape of its orbit around the sun. And that affects global temperatures. So there was a coincidence between some volcanism in the Atlantic and a warm episode related to Malankovic cycles that

They both coincide with the beginning of the Paleocene-Eocene Thermal Maximum. Those two things alone would not have been enough. But what they did is they started to trigger feedbacks like melting of ice, breakdown of permafrost and release of methane and carbon dioxide from permafrost, eventually breakdown of methane stored on the deep sea floor. And so over a period of about 1,000, years. We think the temperature increased by about 8 degrees Celsius and stayed hot for almost 200,000 years. We've been in a glacial period for the last 1.6 million years.

Glaciations have come and gone over that time on a time scale of around 100,000 years, and that's related to Malankovic cycles. The last glacial maximum when most of Canada was covered in ice, parts of Europe, was at about 25,000 years ago. And that's when the Milankovic cycle switched and started towards more warming. And we gradually came out of that glacial period until around 10,000 years ago when the Malankovic cycle switched back again into a cooling phase. but at around that same time, humans started developing agriculture. They were cutting down forests to grow things.

The rise of agriculture and civilization after the last ice age appear to have kept greenhouse gas levels high enough to keep the Milankovic cycle from pushing us into another ice age. So 10,000 years of climate stability, at least until now. So that's one kind of important result of human. The other one, of course, we all know is that a couple hundred years ago or 250, we started using fossil fuels as a source of energy, starting first with coal and then eventually with oil and then gas.

We have been taking fossil fuels out of the earth at a prodigious rate and burning them without really thinking about the consequences, adding carbon dioxide mostly, but also a lot of methane, into the atmosphere and creating what we call anthropogenic. climate change. And we know about these changing levels of greenhouse gases going back almost a million years, thanks to ice cores. Frozen records of air held in ice sheets at the Earth's poles. I think this is really mind-blowing. I mean, there are actually parts of the world where ice has been preserved for hundreds of thousands of years, most notably Antarctica. In the interior, you're actually almost sitting on top of a mountain of ice. What happens is snow accumulates

year upon year upon year. It gets squashed down by the snow that's on top of it. And eventually it turns into ice. And that builds up into an ice mountain. And then you can actually drill back down into it. It's like drilling into a time machine. You're drilling through layers of past snowfall. And in those layers are trapped actual pieces of air. I was actually there when they drilled the oldest ice core ever to be drilled continuously, which went by 800,000 years. I was there when they hit the bedrock, it was a joint French-Italian base, and so they did this big celebration where they had a massive thing of champagne, and they knocked the top off with a great big carving knife. And they gave us all bits of champagne with shavings from the ice that

was at the bottom where they hit the bedrock, and it had inside it air that was 8,000 years old. And they're trapped in little bubbles. It's literally little bubbles. Did you get the bubbles, and you say how much CO2 was in it? What was the air made up of? What was the atmosphere like? in ancient times Antarctica's preserved it like it's a history book of the atmosphere. When you talk about the stability of the molecules in the air, you can divide it into nitrogen and then everything else. Most everything else is fairly reactive and that recycles, we incorporate it into our body, something will happen to it. The nitrogen, however, is extremely stable. So those nitrogen molecules exist for millions, hundreds of millions, billions of years even. So the odds are good that we are still,

every one of us inhales one or two molecules that Caesar inhaled in his last breath. Taranosaurus rexes, Amelia Earhart, Confucius, Genghis Khan, whoever you want. They, in their last breath, you are still breathing the air that they breathed as well. And so how different is the air now from pre-industrial times? Like how different is the air we breathe? from the air that Caesar would have inhaled in his last breath? The major components are the same. Back then, it was roughly 78% nitrogen, 21% oxygen, and 1% other things. And that's the basic constituency of the air now.

But that 1% is really, really important for other effects that it has, most noticeably the greenhouse gas effect. It's the gases present in smaller quantities like carbon dioxide and methane. that are more important and what we have changed over these 10,000 years. But remember that early on in that period of agriculture and deforestation, we were only tens of millions of people on the earth. And then hundreds of millions. And it isn't until the last century or so that we've become billions. So although early civilizations appear to have had had, an effect on the climate. The effect was relatively small, and we don't see that big increase in temperatures happening until we really got started using fossil fuels. It's not just the usual

greenhouse gas suspects that humans have jacked up in the air. Our atmosphere now has a uniquely human signature. We know of a lot of planets right now. Astronomers have found lots and lots of them around other stars, but we haven't found one that has the composition that we have. And what would really make our planet stand out is the trace components, things like industrial gases, chloro-fluorocarbons, things like that. We don't know of any natural way that those kind of gases can be produced. And it's those gases that, as far as we can tell, are unique to the Earth's atmosphere everywhere in the universe. And one of those gases, chloral fluorocarbons, or CFCs, proved to be almost as destructive as oxygen was to early life.

The ozone layer is utterly essential to all life on Earth. It exists in the upper atmosphere, just in the part that we call the stratosphere. And the people who discovered that there was a hole in the ozone layer with three friends, three scientists who were working from a British base in Antarctica. And they were doing balloon measurements just to see what the ozone measurement over Antarctica was. And when they checked, they got this bizarre reading that said there is zero ozone over your heads. The ozone is gone. There is a hole in the ozone there.

And they thought, that can't be true. So they repeated the measurements again and again, thinking but NASA has done this experiment. And we know how much ozone there is and it's all fine. And then they published it and it turned out that NASA's instrument had been told to ignore any results that were obviously wrong. And when it came out was zero, it was a result that was so obviously wrong that they chucked it out. But these three guys are the people who discovered that we were accidentally destroying our own ozone layer. And it turned out it was being caused by an entirely new chemical that had been invented by a wonderful man called Thomas Midgley. Thomas Midgley was a really, it was a lovely guy.

He wanted to make the world a better place. He was working for DeBond. And about the time that he was working, electric refrigeration had just started to come into play. And it was a brilliant thing. You could put it in hospitals and you could keep medicine safe. keep food safe. It was something that's really making the world better. But unfortunately, the refrigerants that everybody was using were things like ammonia, which was poisonous, which burst into flame, which was causing all sorts of accidents. So Thomas Midgley

decided he would make something that was completely harmless. So he invented a new chemical that was completely harmless that couldn't be oxidised, that didn't react with anything in the lower atmosphere, that was completely utterly as far as he was concerned safe. And what he didn't know is he made it so inert, it was so impossible for it to react with anything, that it made it all the way through the lower atmosphere without reacting, made it up into the upper atmosphere, through the ozone layer, where it encountered the deadly rays that the ozone layer protects us from. The deadly rays from the sun then broke it apart

and turned it into a Frankenstein monster, and it began to destroy the ozone layer. So he was trying to help, and he accidentally invented a chemical that nearly destroyed all life on earth. And he never found out what he'd done because he got polio. And because he was such a lovely guy and an inventor, he didn't want to trouble people when he was struggling to get out of bed. So he invented a system of pulleys and ropes that would help get him out of bed in the morning.

And one morning he strangled himself on his own invention. I think he was the world's unluckiest, kindest, nicest inventor you've ever met. He was trying to make things better. Well, you mentioned CFCs as a kind of Frankenstein's monster. And the way you describe it in the book, it seems like it's almost violently ripping apart ozone molecules. So what happens is it goes up into the upper atmosphere, and then it encounters this radiation that comes from the sun that the ozone layer protects us from. And that radiation breaks the molecules up into pieces. And those pieces are very radicals.

And they're the things that they chomp on ozone and regenerate themselves. I picture it's almost like a Pac-Man, as it's just. chewing its way through the atmosphere and creating the holes that we saw at the Antarctic and started almost a sea in the Arctic. And I kind of use the Thomas Midley story sometimes and people say, we can just use technology to fix this or that. I say the history of humans trying to make things better isn't always a good story. Do you have a sense that, you know, the history of humans' relationship to the atmosphere during like, you know, the golden age of science and engineering is kind of this succession of moments of,

hey, we've got this great new development that's going to make everybody's life better, follow decades later by, oh, crap, we broke the atmosphere again. We broke the atmosphere again. I think that it really is a history. And I think one of the reasons is that the atmosphere is so fabulously complicated. It's very hard for us to know what interventions will have the way that circulation happens, the way that wind happens, the way that the chemical constituents happen. And the massive implications they have for what happens on the surface, this ocean of air above our heads, it's not just something to breathe,

and it's not just something that blows things around. It's something that affects everything about the surface of our planet and everything about how we can make a living, how we can eat, how we can shelter ourselves. It's really, it's miraculous stuff, but we mess with it at our peril. Which we still seem to be doing. This year, carbon dioxide levels in the atmosphere reached a record high of 430 parts per million. That's 50% higher than at the beginning of the Industrial Revolution. The air has changed its composition over time, but we've never seen. seen such a quick change as we have in the past 250 years or so.

And quicker warming than even the most dramatic warming episodes in Earth's history. And the one that we probably understand the best is the Paleocene-Thermal Maximum at 56 million years ago. It took about 1,000 years for the Earth's surface temperature to increase by 8 degrees. So 8 degrees over 1,000 years, we've seen 1 degree temperature increase over about the last 50 years. So that would be more like equivalent to 20 degrees over 1,000 years. We're probably at least twice as fast now as any known natural warming event. How much more apt are we to change the air unwittingly than purposefully? I think we're more apt to change it unwittingly simply because we don't think about the long-term consequences of our actions in a lot of ways.

We have changed it unwittingly, and we're doing that for probably about 200 years or so before scientists and then the general public realized what was going on. If we do it wittingly, we usually see something. You know, the air turns a funny color, we smell something. We're usually pretty good about jumping on those kind of things because we know it's bad for us. But so far, we're just kind of doing it. I mean, we were doing it unwittingly at first, and now we're doing it wittingly. And we are kind of performing an unfortunate experiment with the air right now. How do you account for the fact that humans seem to have such a kind of almost antagonistic sort of self-sabotaging relationship with air?

If you look at places like Delhi or across cities across China, one of the reasons that they're acting on shifting away from coal is because they can't breathe. And that's very visceral, and that's a good driving force for why China is acting on climate change. So, you know, maybe part of it is that we, if we do connect our ability to breathe, we do something about it, but we don't connect air with warming temperatures or fires or floods.

It's a bit of a harder connection to make. But it's getting harder not to notice the air or its effects. 15,000 deaths are caused by air pollution per year in Canada, and wildfires are devastating air quality along with forests. We're also more aware of the air simply because of its heat, how clingy and oppressive it feels. Warmer air can hold more water vapor, and that makes it feel hotter still, and warmer, wetter air also means more extreme weather.

And there's another thing warmer air does. It triggers feedback mechanisms that warm the air and increase, greenhouse gas levels, yet more. There's quite a lot of methane stored in permafrost. And when that permafrost breaks down and that soil gets eroded, the methane is released. And that's a significant greenhouse gas. There's also methane stored on the seafloor in a form that we call methane hydrates. It's always been there.

Past big climate changes have probably resulted in release of some of that, and that's a feedback. And there is the potential in the future, not in decades, but maybe within centuries, that deeper parts of the ocean will warm enough to destabilize that seafloor methane hydrate. There's as much warming potential in the seafloor methane hydrate as there is in all of the coal, oil, and gas that's available to us at surface. It's potentially a huge warming. It probably was part of what caused the Paleocene-Eocene Thermal Maximum. It's probably part of what caused the big extinction 250 million years ago. So that's really important.

And we need to think more about that for our future. So if we did replicate that kind of thermal maximum, what would the implications be for life on the planet and human civilization? Human civilization would take a really big hit because we're not set up to, withstand several degrees of warming. We're suffering under what we now have is close to 1.5 degrees and things like food production would start to decline rapidly and our civilization depends on food production and it's not going to last very long if the temperature increases as fast as it could with all these feedbacks coming. That kind of warming would likely also affect the course of

evolution, including our own. So you see more extreme weather events right now. You see warming in places where creatures just can't handle it. Islands, mountains, these sort of vulnerable environments. So you see species being driven extinct from that. So in the short term, that's what is doing to evolution. Over the long term, it could remake our body in some ways. We'll probably be shorter than we are nowadays in a much warmer world. Our hearts will probably get smaller. We don't need as large a heart in a warm world. We'll probably have bigger ears to help dissipate heat from inside our body. And we'll probably have longer limbs to help dissipate heat as well. How long is the carbon dioxide that we've put up in the atmosphere? How long are we stuck with it?

It will eventually come out of the atmosphere, but it's pretty stable up there. We're probably stuck with it for a thousand years. Photosynthetic life will continue to take some of it out, but there are other processes that will continue to put carbon dioxide into the atmosphere. So, yeah, we are stuck with it for quite a while. So we need to start drawing down the carbon dioxide level. We haven't actually even seen all the warming that that will produce, just because it takes time for that kind of warming to actually come into effect.

So even if tomorrow we stopped using fossil fuels and started using other forms of energy and other ways of getting around, the carbon dioxide level and the methane level are certainly not going to drop overnight or even within a few years. They might even continue to go up a little bit, but then they'll start to drop, but the temperature isn't going to respond as quickly. So even if we stopped using fossil fuels,

now. We're going to see more temperature increase and some of the feedbacks that we have triggered might still keep going because they're slow processes, but it's what we need to do to start turning this around because our civilization can't survive the kind of climate change that is likely to be happening. But we did manage to stop the production of CFCs with the Montreal protocol. We also had, you know, there was the problem of acid rain that really came to the four in the 80s, and that was addressed by a treaty between the U.S. and Canada, stopped putting lead and gasoline. What do you see is the difference between the way humanity, leaders, governments, civil society addressed those kinds of atmospheric crises and climate change

and the general kind of inertia around getting serious about reducing. green-hose gas emissions. So I've asked myself this question a lot because we certainly did. We understood about acid rain. It took a little while and then we figured out what the problem was and we fixed it. The same with CFCs and we fixed that too. So why not climate change?

I think there's several reasons. One of them is that climate changes, it's a very slow paced. It happens over decades the changes that you're seeing. Days pass, years pass and things get a little worse, a little worse. But again, it's that cumulative effect over time. It's hard

for human beings to really grasp that. We're just not wired for that kind of thinking. I've been working on climate change. I've been speaking about it, writing about it, and working on it for more than 30 years. And at the beginning, it was quite hard to find images to illustrate my talks to say, this is what we're predicting, will come,

and now it's quite hard to choose, which wildfires, devastating continents, which floods, which storms, which intensification of rainfall, which rising sea levels, and the effect that they're having. There's so many now that it's really become not subtle. But by now, something else is kicking in, really,

which is that we depend for all of our living, really, for our successful ways of doing business on this stuff that we've got addicted to, which is coal and oil and natural gas. Burning that has made us rich, burning that has made our lives comfortable and good in many parts of the world. And in other parts of the world,

who aren't able to use those things, they're suffering disproportionately from the consequences. And so those countries are saying, why shouldn't we be able to get rich the way that you have? And in the meantime, the countries that have, like the US and Canada and the UK, that have made themselves rich on the back of fossil fuels, don't want to give up those lifestyles. And so I think that there is a widespread perception

that the only way to handle this is to go back to the caves, have to give up our things that we really care about. I think it's a very wrong narrative, but it's one that's taken hold in a lot of people's minds and hearts. Really, we need to be getting inventive about creating solutions rather than saying this just means we have to give up everything. I think we underestimate collective action because we all have a tendency to think, well, it's just one small thing that I'm doing.

It's hard for the human mind to grasp the magnitude of 8 billion people doing one small thing every day that's contributing to it. our imaginations struggle with that. This isn't really the same atmosphere we humans evolved to live in. This isn't even quite the same atmosphere your grandparents grew up in. It says something about our relationship to air in the Anthropocene that we've made it hot enough that now we have to artificially cool it. Air conditioning isn't a luxury in parts of Canada.

In extreme heat, it can be a matter of life and death. And if we're going to slow down or ultimately a rest or even reverse climate change, humans will have to alter the composition of the air, intentionally this time. What everyone says about reducing what we consume and mitigating the effects, those are going to be an important part. So I don't want to act like that's not a good idea or reject that. But as I talk about in the book, human beings are not very good about doing those kind of things. We all have our little luxuries that we're reluctant to give up.

So some things we are looking at technologies involve getting greenhouse gases out of the air, so kind of stripping the carbon out of the air. Another wilder solution that people have talked about is releasing sulfur dioxide high in the atmosphere. So when we've had giant volcanic eruptions in Earth's history, that releases a lot of sulfur dioxide and that goes up in the upper atmosphere, and it reflects sunlight back into space. So that could be one way to at least lower the temperature somewhat. The problem with that is that you need to continually be putting sulfur dioxide up into the atmosphere.

So it's a very labor-intensive process. It's sort of like getting on a treadmill. You can't stop once you're on this treadmill. The other problem would be it would probably change the color of the sky too. So we would lose the blue skies that we're used to, which would obviously be quite heartbreaking and disappointing. Another possibility is using bacteria, essentially seeding large parts of the ocean to increase the activity of certain microbes that can also get carbon dioxide and other pollutants out of the air. So those are some of the ideas that people have thrown out there to try to mitigate the mess that we're in. And it all sounds a lot more like a big Rube Goldberg kind of device than actually maybe not producing so much carbon dioxide.

dioxide. Yeah, that would be a better solution, clearly. It's just that we're kind of on this path, and I do think more people are taking it seriously, which is good. I think, sadly, we're seeing the dynamic weather and the more extreme weather. You know, wildfires, hurricanes are getting more intense, things like that. So people are starting to wake up in some ways. And I do think that the protocols and things are helping and have help. I just, again, am skeptical. I'm skeptical. that human beings are going to sort of stop doing what we have been doing for years and we're just not doing that. And so I think in some ways the technological fixes are kind of crazy sounding, but I think in some ways they might be our best bet.

But that's also why I'm working on carbon removal, which is actually reversing this process of just pouring these pollutants into the atmosphere and watching them destroy our climate and then just hoping for the best. What we need to do is say, let's stop creating the problem, let's shift from burning fossil fuels to solar power and wind and cleaner forms of energy and electrification and all of that. Let's use our human ingenuity to stop polluting the atmosphere. I don't think about it as engineering the air.

I really think about it as kind of cleaning up our mess and taking back out the CO2 that we put in. And I'm really optimistic about this. It feels like every day there's a vivid new, approach to how you could reverse this process and take CO2 out of the atmosphere. So it turns that you can do it with trees. Trees are fantastic carbon capture devices. They make their entire bodies out of thin air. That still blows my mind that they don't get their bodies out of the soil or anything. They get it out of the air. And so they're great at capturing CO2. But you can

also trap it in soils. You can do this thing. There's quite a lot of work on this in Canada, which is fantastic. It's turning rocks into sponges that take up CO2. Rocks naturally do that over tens of thousands of years. But if you grind up the rocks, the way that grinding up coffee beans means that you can make coffee more quickly, if you grind up the rocks and spread them on fields, they act as sponges for CO2 over maybe 10 years. And you can also use fans to blow air over capture devices and literally catch the CO2 in a blimp. And in many cases, they're putting it back where it came from, reversing the valves. So it goes back where the oil and gas came from in the first place. And so I think, you know, poor Thomas

immediately humans try to invent something new and make a mess of it are on one side. But on the other side, the humans who say we understand what we've done, let's use our ingenuity to take it back. And I think we really will be at the stage where we can take billions of tons of CO2 back out of the atmosphere and keep it out in the next 10, 15 years. Well, I hope you're right. Watch this space. You know what they say, you can't predict the future, but you can create it.

And so that's what we're aiming to do. Well, thanks very much, Dr. Walker. I really appreciate it. That was great. I enjoyed it. Gabriel Walker, a climate scientist and the author of An Ocean of Air and Snowball Earth. You also heard acclaimed science writer Sam Keene, whose books include Caesar's Last Breath, and Stephen Earl, the author of A Brief History of Earth's Climate. This episode was produced by Chris Wadskow. Our website is cbc.cai.c.com, and you can find us on the CBC News app and wherever you get your podcasts.

Technical production, Emily Kiervasio, Sam McNulty, and Danielle Duval. Our web producer is Lisa Ayuso, senior producer Nicola Luxchich. Greg Kelly is the executive producer of ideas, and I'm Nala Ayyad. For more CBC podcasts, go to CBC.ca slash podcasts.