Air Date: Week of March 27, 2026

Published in August of 2025, The Story of CO2 Is the Story of Everything explains how crucial carbon dioxide is for life on Earth. (Photo: Courtesy of Ecco Press)

Over billions of years of its history, the planet has frozen over almost completely and then lost all its ice as crocodiles basked in a balmy Arctic. Carbon-based life arose and adapted to all this change. And at the center of it all is the notorious greenhouse gas, carbon dioxide, the focus of journalist Peter Brannen’s book The Story of CO2 Is the Story of Everything: How Carbon Dioxide Made Our World. He joins Host Jenni Doering to describe the extreme climate whiplash of Earth’s past.

Transcript

DOERING: Over billions of years of Earth history, the planet has gone through a lot of change — to put it mildly. Earth froze over almost completely, more than once, and then lost all its ice as crocodiles basked in a balmy Arctic.

CURWOOD: Over and over, continents have collided to form supercontinents like Pangea and then been wrenched apart again. And, of course, carbon-based life arose, adapting to all this change and eventually leading to you and me.

DOERING: Well, much of all this has to do with the notorious greenhouse gas, CO2. And to explain how, journalist Peter Brannen wrote The Story of CO2 Is the Story of Everything: How Carbon Dioxide Made Our World. He joins me now. Welcome to Living on Earth!

BRANNEN: Thanks so much for having me.

DOERING: So one of my favorite quotes from the book is from the intro, and it goes, "Today, as in the beginning, life is still made out of carbon dioxide, and the world's problems are made out of carbon dioxide as well." This feels to me like a thesis for the whole book. Can you talk to me about that?

BRANNEN: Yeah, so my motivation for writing the book was sort of to pull back from the headlines and reintroduce people to this thing that they read about in the news, carbon dioxide as this industrial pollutant that comes out of smokestacks that causes warming and all these bad things on our planet. I mean, I sort of wanted to reintroduce the reader to this idea that this stuff, CO2, for some reason, really is fundamental to how the planet operates and has been maintained over hundreds of millions of years, and that while in certain times in Earth history, like right now, when lots of it goes into the atmosphere all at once, it causes warming and all sorts of scary stuff. But in the bigger picture, it has this sort of miraculous centrality to the story of life on Earth, where not only does it cause warming when there's too much of it, it also maintains a habitable temperature for animal life on Earth. If you took it all out of the atmosphere tomorrow, the temperature would drop by something like 60 degrees Fahrenheit in a half century, and probably freeze the ocean of the tropics. But there's also this other miraculous feature of it, that all life is literally made out of the stuff. So I'm sure people have heard that we're carbon based life here on Earth, and the source of that carbon is CO2. So our story, as the story of all animal life, has been one of living off of this magic trick, photosynthesis, that turns CO2 into the stuff of life. At the same time that we have this habitable planet where the temperature is just right for animal life, which is pretty finicky and can only live within a pretty narrow temperature range. I weave those two threads together and sort of today, the story is the cataclysmic collision of those two features.

DOERING: One of my favorite parts about reading your book was how much I felt like I was there watching Earth history unfold like some kind of film on fast forward. And one of the really fascinating parts about this Earth history is the numerous times when the climate really went haywire, and CO2 has a lot to do with that. So talk to me about what on earth happened when the planet turned into Snowball Earth?

BRANNEN: Yeah, so it's kind of incredible. Over hundreds of millions of years, for the most part, the planet has navigated this really narrow window of habitability, but sometimes things go haywire in ways that are relevant to our current moment. I talked about extreme greenhouses when CO2 goes up too fast in Earth history, hundreds of millions of years ago. But then, yeah, I also talked about this thing, Snowball Earth, around 700 million years ago. There's a couple amazing things about Snowball Earth. One is just how severe it is. So what it is — it's almost exactly what it sounds like — a global glaciation that lasts for 60 million years, briefly thaws, and then goes back into a basically global glaciation again for a couple million years longer. And so it's incredible, because it's both so extreme, the temperature at the poles might have been almost cold enough to freeze out CO2 from the atmosphere, like you only see that on Mars. So we're not even talking about Earth anymore. This is like a different planet.

DOERING: Wow, frozen CO2 at the poles. Wow.

BRANNEN: Yeah, which is potentially incredibly dangerous because you could potentially get into like a fatal, eternal Snowball Earth. Animal life would never arise. The other amazing thing about Snowball Earth is after it's over, after 4 billion years, where the most interesting thing the planet has made to that point is microbial muck. In the wake of Snowball Earth, you get this explosion of large, complex life, and eventually the rise of animal life. But it's a CO2 story like you know all the others in my book because one of the leading ideas for why the Earth suddenly plummets into this ice catastrophe is that, just how we're worried about CO2 going up too fast today and getting too warm, you can also have this other threshold on the other side, where, if it drops down too far, you can potentially drop into this ice albedo planetary catastrophe, where, you know, it almost freezes solid.

DOERING: Wait, so why did the world not stay forever frozen?

BRANNEN: Well, I guess to set this up I need to explain what these big geological processes are that sequester CO2. And the main one over millions of years is this thing called rock weathering, which is kind of just what it sounds like, which is when CO2 reacts with rain water, it makes it more acidic, and that rain water reacts with rocks, and eventually what was once CO2 in the air gets washed out into the oceans and precipitates as things like shells and limestone. And so, what was once CO2 becomes, you know, rock at the bottom of the ocean. That's the planet's main sort of thermostat for getting rid of the stuff. But in Snowball Earth, when you suddenly cover up all of the land with ice, none of that precipitation is reacting with rocks. So you're not burying any CO2, but you still have this steady stream of it from volcanoes that are emerging out of the ice sheets. And, you know, when aren't humans around, volcanoes are the main source of CO2 for the planet. They emit it at about 1/100 the rate that humans do. But you can imagine, if you're in a Snowball Earth situation, you have no CO2 being buried, and you're just in this ice world, but you still have these volcanoes puffing into the sky. So it's just building up and building up and building up over millions of years until suddenly it reaches this insanely high CO2 concentration. So, I mean, today, we're worried rightly, that CO2 is now 420 parts per million, which is concerning because CO2 hasn't been that high in 3 million years when the sea level was a lot higher and it was a lot warmer. With that context, now apply that to what might have been the case the thaw of Snowball Earth, where CO2 might have gotten up to something like 100,000 parts per million.

DOERING: 100,000 … oh, my goodness.

BRANNEN: Yeah, right. And I mean, you need it to get that high in order to thaw global glaciation. And so the aftermath of Snowball Earth is extremely hot and chaotic.

DOERING: Wow.

BRANNEN: Like we know something that crazy happened because the thaw out of Snowball Earth is absolutely wild, at least the fossil record of it. There's estimates that the whole thing melted within a few millennia, and suddenly the planet was covered in like a mile deep lid of 120 degree fresh water from all the melted ice. There's evidence for, like, the wildest weather in Earth history, where you just see these, like, really long period waves that left behind these ripple marks in the sea floor. You know, it's kind of amazing that life, or complex life, was forged by the most extreme climate catastrophe in the planet's entire history.

DOERING: Wow, it must have been a crazy world. One of the parts that I found really interesting in this book was the section about Pangea, and I think most of us think of it as the home of the dinosaurs, but it was also the setting for a series of mass extinctions. What was Pangea really like?

BRANNEN: Pangea? Yeah, I think there is this sort of popular understanding, as you said, like this is where dinosaurs lived, and the story of dinosaurs originates on Pangea, but they really take over once it starts to break apart at the end of the Triassic. And before that, it was this kind of miserable time for life on Earth where a few tens of millions of years, depending on how you count them, there are multiple mass extinctions, including two of the biggest ones ever, and the biggest one ever, by far, this thing called the End Permian mass extinction. So there's a sort of long, weird prehistory. If you imagine you have a giant supercontinent, it would be very hard for weather to reach the interior of it. And so for the most part, Pangea had this vast, arid interior, and the planet seem to really struggle to make it through. As I said, there's these two major mass extinctions. And the reason why I focus on these mass extinctions is that unlike the one that wiped out the dinosaurs, that seems to be mostly driven by a big rock falling out of the sky. That's not really relevant to our story today as human beings, where we're worried about CO2. But it turns out there are these older mass extinctions before the age dinosaurs that were caused by huge eruptions of carbon dioxide into the atmosphere from these mind-bending volcanic eruptions. So one I really focus on is the End Permian mass extinction. It's the biggest mass extinction by far. Paleontologists went back to this much bigger one looking for evidence of asteroid impacts. There really isn't any convincing evidence for an impact. And instead, what there is is there's this huge swath of Siberia, which you can even see it on Google Earth today. It's sort of this grayish brown stuff that covers a lot of Siberia, are these ancient lava flows, and they date exactly to the moment of the mass extinction 250, 200 million years ago. To give you some perspective for how mind blowing these volcanoes were, they erupted enough lava and enough magma intruded into the crust that it could cover the lower 48 United States, a kilometer deep in lava.

DOERING: And all that lava and magma comes with a lot of CO2.

BRANNEN: Right. As crazy as that is covering a lot of Russia in lava, it doesn't explain why things at the bottom of the ocean on the other side of the world are all going extinct at the same time. And for that, you really need the gasses coming out of the volcanoes to change the chemistry of the whole planet. And the one that geochemists have really honed in on is CO2 because geochemists have all these very clever ways of analyzing rocks, and they've teased out what looks like a huge change in the planet's inventory of carbon itself. Seems like there's a huge eruption of carbon dioxide. You can tell it gets really hot. The best estimates are like ten degrees C warming over a few thousand years. The oceans acidify, which is what happens when too much CO2 reacts with sea water. We're seeing it today on our own planet. So the Permian really is the worst case scenario. If you want to know what happens what we're doing today, just several centuries into the future, if we just keep our foot on the gas, you can eventually end up at this like planetary Armageddon, essentially, which is the End Permian. So it's sort of this helpful cautionary tale in the rocks of what can happen.

[MUSIC: Chris Isaak, Martin Winch, “Wicked Game” on Espresso Guitar, Murray Thom and Carl Doy, THOM PRODUCTIONS LIMITED 1998]

DOERING: We’re speaking with Peter Brannen, author of The Story of CO2 Is the Story of Everything. We’ll be right back with more after the break. Stay tuned to Living on Earth.

ANNOUNCER: Support for Living on Earth comes from the estate of Rosamund Stone Zander — celebrated painter, environmentalist, and author of The Art of Possibility — who inspired others to see the profound interconnectedness of all living things, and to act with courage and creativity on behalf of our planet. Support also comes from Sailors for the Sea and Oceana. Helping boaters race clean, sail green, and protect the seas they love. More information @sailorsforthesea.org.

[MUSIC: Chris Isaak, Martin Winch, “Wicked Game” on Espresso Guitar, Murray Thom and Carl Doy, THOM PRODUCTIONS LIMITED 1998]

CURWOOD: It’s Living on Earth, I’m Steve Curwood.

DOERING: And I’m Jenni Doering. Let’s get back to our conversation with Peter Brannen, author of The Story of CO2 Is the Story of Everything. That title isn’t exaggeration. All known life on Earth is made of carbon dioxide and the other carbon chemistries it cycles through. It’s also the primary thermostat for the Earth, and anytime the Earth has seen changes in atmospheric CO2, the planet has experienced extreme climate whiplash. Before the break, we took a wild ride through the Earth of hundreds of millions of years ago, from the very low CO2 world of “Snowball Earth,” to the hothouse planet that resulted from massive volcanic eruptions releasing astonishing levels of CO2. Now, humanity has its finger on the thermostat, as we burn fossil fuels and release tons of carbon dioxide and other planet warming gases.

BRANNEN: Climate, to put it charitably, "skeptics" in quotes will sometimes point to times deep in Earth history where CO2 was higher and it was warmer and life was happy, which is 100% true, but it's pulled out of its geological context. Where these changes usually take place over tens of millions of years, where CO2 will rise and fall based on planetary processes and changes in volcanoes and subduction zones and where continents are. And it's true that 50 million years ago, there were crocodiles and palm trees in the Arctic Circle, and CO2 was higher and life was happy. But it took tens of millions of years of planetary evolution to get to our world, which is significantly colder and lower CO2. And just reimposing that change in a few decades to centuries, where everything today is evolved for our world into sort of the greenhouse of the dinosaurs is sort of a shock that you don't see from Earth history. And it really is such a narrow window. Like, it's kind of mind blowing how little CO2 makes the difference. The difference between that world I was just talking about with crocodiles and palm trees at the Arctic Circle and the depths of the ice ages, that was difference between .1% of the atmosphere was CO2 and .02% of the atmosphere of CO2. So when things aren't going out of control and mass extinctions, or like since the Industrial Revolution, it's kind of incredible and sort of awe-inspiring that the planet manages to maintain it at just the right level for life on Earth. And it does subtly change, and it does change the climate over millions of years, and that does change life on Earth, which is very adaptable and can evolve, but there's speed limits to that, and what we're doing now is just exceeding the speed limit for life on Earth's adaptive capacity, like you see in the mass extinctions. Hopefully we don't go as far down that road as you see in Earth history, but it’s kind of amazing.

DOERING: With all of the change that's happened — I mean, huge swings in the climate — life has somehow managed to find a way to survive, but I suppose that this planet was always changing, and we always had those swings. And so life has really been pushed and pulled, and it's had to adapt, and here we are today, and for whatever reason, complex life emerged.

BRANNEN: Yeah, I talk about in the book how human evolution and the evolution of everything else on the planet really is fundamentally shaped by changes in CO2 over millions of years. The story of the age of mammals, so since the asteroid wiped out the dinosaurs, we basically inherited the high CO2 greenhouse world of the dinosaurs. And over tens of millions of years, CO2 has been declining until suddenly, in the last, you know, three million years ago, we started going in and out of these really deep ice ages where the planet had finally lost enough of its CO2 blanket that small changes in the planet's orbit and tilt and things could plummet the planet in and out of these huge glaciations that fundamentally shaped human evolution. And there's a similar story for plants started evolving form of photosynthesis that's more efficient at lower CO2, once CO2 had declined enough. There's an argument that baleen whales got so big during the ice ages as sort of an adaptation to this cold world. So life on Earth, fundamentally, is evolved for the world of the last few million years, not the world of 50 million years, 100 million years ago.

DOERING: So Peter, in the very last moment, basically, of Earth history, up till now, we humans arrive, and as you write, we are an ice age species. But you know, we're scrawny. We're hairless creatures. We prefer temperatures, at least, I prefer temperatures above 70 degrees Fahrenheit. So what do you mean by ice age, and what climate are humans evolved for?

BRANNEN: Yeah. So the last two and a half million years have been really volatile, where we have dropped into these deep ice ages. First they were 40,000 years, and then they started getting deeper and longer 100,000 years in the past, you know, million and a half years. And then you'll have these brief breaks between the ice ages called interglacials, where it's sort of these planetary spring times for a few 1000 years, but then you'll go back into an ice age. And so this is a really volatile world where you have to be incredibly adaptive to survive. And it wasn't our thick hides or our big fangs that kept us alive during this period, it was culture and the ability to pass down technologies over generations and reorganizing societies adaptively to a changing landscape. You can obviously imagine why having such a close relationship with fire would be a useful thing during ice ages. It allowed us to not only stay warm in higher latitudes, but also cook our foods, which allowed us to have these huge brains because a lot of other primates and mammals have to spend a lot of their day chewing their food and digesting it. And so you have to invest in larger colons and bigger chewing muscles and big molars and things. And we're just undersized in all those categories. And it's because we've outsourced all of our digestion to this stuff fire that does a lot of the work for us. And instead, we get to invest our energy in these massive brains that allow us to have language and culture and technology and all these things that allowed us to survive the ice ages. So there's a lot of reasons to be worried about what's going on today, but when people ask me, "What's your hopeful story?," I don't know what the next few decades are going to look like because I'm as worried about the headlines as everyone else. But if you look at our history, it's kind of an inspiring one of adaptation and our ability to innovate, both technology-wise, but also societally. So I think that ultimately, we're going to figure out a way of living on this planet that is more in keeping with these big global, planetary cycles that I talk about elsewhere in the book. So the very things that ice age forged in us to keep us alive, I think, are our best hope for keeping us alive in the future.

DOERING: Before reading your book, I don't think I had really understood just how much of an edge we get from this external metabolism, as you call it, you know, from using fire, using heat to transform lentils or grains into things that are more easily digestible, that give us the energy that we need to power the work that we do.

BRANNEN: Fire, yeah, is fundamental to our survival. I think someone in a science paper says we're the only obligate pyrophile. But I also tie it into the fact that, you know, this is a precondition for the Industrial Revolution. You know, we've been using fire in the same way that we had for the entire Pleistocene ice ages. But then you start having people use it to brew beer or evaporate brine to get salt, and so we've put it to use in all sorts of other ways. But then the thing that took the lid off the Industrial Revolution was the steam engine because finally you were able to use fire to literally do work on the surface of the planet and essentially automate human labor with these machines and things. And once you tie that ability to do work with fire through these weird steam engines, and you connect it with all of the plant energy that's ever existed in all of Earth history, these things called fossil fuels. So, basically, the legacy of the entire history of life on Earth in the past few centuries, we've brought up to the surface and basically just lit it on fire. So there's no way to do that without completely transforming the surface of the planet. And I think sometimes we don't really appreciate how uncanny and weird it’s that we're digging up all the plant life that's ever existed in Earth history and putting it to work for us.

DOERING: The reason we have this Industrial Revolution is because we are finding and digging up and burning coal at first, and then oil, and ultimately, that stuff is just the product of ancient photosynthesis. Tell me about how it’s that the Earth has collected so much of this coal and oil and other fossil fuels that we are now digging up out of the Earth.

BRANNEN: Yeah. So the planet has also not only compiled the history of life, but it's also literally, it's the burial ground for all of the history of life. So sometimes you'll find dinosaurs, but much more frequently, or much in much greater volumes, you'll find the remains of old plant life, essentially. So when it's on land, it's coal, and what's in the oceans, big algae blooms and stuff that turns into oil and gas. So yeah, I mean the same rocks we frack today for natural gas, you can find incredible fish fossils and things. And so, over hundreds of millions of years, as we've built up the fossil record, we've also built up this unbelievably huge reservoir of old, living stuff that is still carbon to this day. I remember going to Upstate New York and looking at fossils on Lake Erie, and you'll crack them open, and they'll smell like gasoline, basically. In the book I write about the eerie encounters people would have in Appalachia in their early 20th century, encountering this period called the Carboniferous, which, if Pangea is a long time ago, Carboniferous is even older than that, and it's an even more alien world, where it was a world of gigantic insects, and you have these vast rainforests from Kansas to Kazakhstan, as one geologist puts it evocatively. And this is the world that these miners would have been encountering. And I took a tour with a geologist in Appalachia. And if you go down there and you look in the mines, you look at the ceilings, there's these fern impressions. In fact, one of the leading causes of death for miners in the early 20th century was literally petrified tree stumps falling out of the ceiling and crushing them. So, they were having this encounter with this 300 million year old world in service of digging up this old plant life and using it to power industrial civilization. So we really do live in one of the strangest moments in all of Earth history.

DOERING: What did you take away most from writing this book?

BRANNEN: Even though it might sound gloomy, a lot of the stuff that I've been talking about, I ended the experience of writing the book just with this sense of cosmic gratitude that I was even alive to begin with, or that we're able to have this conversation. When you read about all the incredible contingent things that happened in Earth history to get us to the point where finally, I can be alive and have a breathable atmosphere. It's just kind of miraculous, A, that the Earth was never completely, you know, animal life was never wiped out completely, even though things got pretty close. But it really does take this four billion year span to get to the point where I get to be alive for a couple decades and look around this weird planet, meet all these cool people, and try and figure it out. And so I feel really lucky in that respect. The Earth is an unbelievable place. It's a miracle that we're alive. And given how precious it’s and how miraculous that is, it just redoubles my conviction about how important it’s to preserve it and be good stewards of the planet and be appreciative for being alive to begin with.

DOERING: Peter Brannen's book is The Story of CO2 is the Story of Everything. Thank you so much for joining us, Peter.

BRANNEN: Thanks so much for having me.

 

Links

Purchase a copy of The Story of CO2 Is the Story of Everything (Affiliate link supports Living on Earth and local bookstores)

Learn more about Peter Brannen’s work.