Transcript: Hope for the Climate: Michael Mann, OUR FRAGILE MOMENT

We talk with eminent climate scientist Michael Mann about climate, past, present and future. His book is Our Fragile Moment: How Lessons from Earth’s Past Can Help Us Survive the Climate Crisis.

The climate crisis is ever more urgent. Is it too late to do anything about it?

What the models tell us is, if we fail to make meaningful reductions in carbon emissions and move away from fossil fuels, we can create a dystopian future that resembles some of the most dire events that we see in the past, mass extinction events. That's a possible future if we don't act. But if we do act, we can certainly avert that sort of future. So the message is indeed one of urgency — we do need to take far more action than we've taken so far — and agency. It's not too late to act to prevent the worst consequences. — Michael Mann

Introduction

We Are Not Doomed To Climate Apocalypse

The world is largely past climate denialism, except for the Republican Party and its fascist leader, Donald Trump. But what has replaced it is climate doomism, the notion that it's just too late to do anything about climate disruption, so we might as well continue with business as usual.

But as eminent climate scientist and communicator Michael Mann tells us, it's not too late to do something to save us from climate apocalypse, and there is resilience in the climate system if we can just give it enough support to kick in.

In Our Fragile Moment, Mann explores what past climate shifts tell us about that resiliency, and what factors have undermined it in the past to lead to the greatest mass extinctions, like when oxygen-creating bacteria depleted the atmosphere of planet-warming methane and caused the Earth to become encased in ice, Snowball Earth.

But enough of life remained in tiny refuges that a whole new oxygen-breathing form of life became possible, and eventually led to — us. Now we could be like those planet-killing bacteria.

But that fate is not pre-ordained. The conditions that allowed humans to live on this Earth are incredibly fragile, dependent on a climate system that is vastly complex, with influences that can drive us further away from a habitable planet, and others that can help restore balance.

In Our Fragile Moment, Michael Mann explains the complex science behind our climate system in a way that makes the subject easily understandable and compelling to read.

He explains why sea level rise is baked in for centuries, but if we stop polluting our atmosphere with greenhouse gases, global temperature will quickly stabilize. It's up to us to make sure that stabilization happens as soon as possible, so we can keep our planet within habitable bounds.

[The following transcript is lightly edited for reading ease.]

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Interview

Francesca: Michael Mann, welcome back to Writer's Voice.

Michael Mann: Thanks, Francesca. It's great to be back with you.

This is just a terrific book, and such an important one, Our Fragile Moment, how lessons from Earth's past can help us survive the climate crisis. It answered so many questions that I've had for years.

The book's key message is one of, as you say, urgency and agency. Explain what you mean by that.

Thanks. I really appreciate those comments.

What I wanted to explore here was what the paleoclimate record, the record of past change in Earth's climate, really tells us about Earth's climate system, particularly with respect to the challenge we face today of human-caused planetary warming and human-caused climate change.

One of the things that I had noticed — in fact, it was the subject matter of my last book, The New Climate War, was, as we move away from denialism, it's very difficult for climate deniers anymore to gain much currency in our discourse because it's clear to the person on the street that something's happening, that our climate is changing, [with] these unprecedented extreme weather events that we see so regularly now, the records that were just set this last year in global temperature. You can't deny it's happening.

So polluters and those sort of promoting their agenda of climate inaction, of sort of business as usual, continuing our addiction to fossil fuels, have engaged in other tactics. And that was what that last book was about.

And one of those tactics is doomism: convincing us it's too late to do anything. It's beyond our control. And ironically, you know, that potentially leads us down the same path of inaction. And a lot of good-hearted, well-meaning people have fallen victim to that framing, that doomism.

And some of it is premised on the paleoclimate record, claims of past events that somehow demonstrate that we have caused runaway warming and there's nothing we can do about it. So I wanted to drill down and really explore what the science has to say about those past events and explain what the science has to say.

And in the end, the lessons that we draw from Earth's past climate history actually are completely opposite to the doomist framing and messaging that we too often encounter.

What it tells us is that the climate models that we use today, the same climate models that tell us that we can still prevent catastrophic warming through a rapid reduction in carbon emissions, those models actually do a good job in describing what happened in the past. It's reason to have faith in these models and to take them very seriously.

And what the models tell us is, if we fail to make meaningful reductions in carbon emissions and move away from fossil fuels, we can create a dystopian future that resembles some of the most dire events that we see in the past mass extinction events. That's a possible future if we don't act. But if we do act, we can certainly avert that sort of future.

So the message is indeed, as you said, one of urgency — we do need to take far more action than we've taken so far — and agency. It's not too late to act to prevent the worst consequences.

And that is such a hopeful note, a hopeful note, of course, with the warning. The book does deeply go into the science of climate. And I want to thank you for making it understandable to the general public, because it did, as I said before, answer so many questions.

Embracing Scientific Uncertainty

One thing that struck me is how incredibly complex the science of climate change is. There are so many different factors that go into understanding it. So before we dive in into it further, talk about the scientific process of investigating climate change and how we must, as you write, embrace scientific uncertainty.

Thanks for that question. When I talk about the importance of embracing uncertainty, there's this anecdote that I tell from my good friend Ira Flato of Science Friday. Years ago, he reported on a congressional committee hearing about the dangers of supersonic transport back in the 1970s. And I think it was Senator Muskie, who was the chair of this committee.

And one of the scientists who was testifying came in with these two stacks of papers. And he pointed to them [and] said, “on the one hand, there are these scientists, there's this work, that suggests that this could be a real environmental problem, a real environmental crisis. On the other hand, there's this set of papers that doesn't really come to that same conclusion.”

And apparently Muskie got very frustrated and said, “Can somebody just bring me a one-handed scientist?”

And so I just had to tell that anecdote, because it underscores something that's intrinsic to science. There is uncertainty, but no, we can't look for one-handed scientists to save the day, because we have to understand that there is uncertainty, and we have to make decisions in the face of that uncertainty. And sometimes that uncertainty has the opposite implications of what some critics would like you to think.

Climate critics would like you to think that, because there's uncertainty in climate science, that's somehow cause for complacency or inaction, when it's just the opposite.

If we look at the history of how the science has progressed, the more we learn about the system — and it speaks to the complexity that you're talking about — the more we understand that there are very dynamic components of the climate system that are more sensitive to warming than our earlier models really captured.

And, for example, the ice sheets are very dynamic. They're not just piles of snow and ice, but they are structurally very complicated. And under certain circumstances, they can become very fragile, they can crack, you can get fissures with meltwater that penetrates to the bottom and lubricates the base of these ice sheets so they slide, and they can calve into the ocean far more quickly.

We're just starting to really capture the full dynamism of these ice sheets and the climate models that we use. And what we're finding is that they're more sensitive to warming, and there's a potential for greater loss of ice from Greenland and the Antarctic ice sheet, and the potential for greater sea level rise than we thought just a decade or two ago. So uncertainty isn't our friend. If anything, uncertainty is a reason for even greater precaution.

And so I felt it was important to really explore that in the book and to really delve into that early on so that the reader gets a sense of why we have to dig into sometimes seemingly arcane and technical matters. And the reward is that in the end, we'll really have a better appreciation of how not only climate science works, but how science in general works.

After all, if a doctor tells you you're pre-diabetic, that's not a license to go out and eat a lot of cake.

That's exactly right. It's close to home because I have to watch my own diet these days to make sure I stay healthy. So I appreciate that example there.

So you say, and I've heard this before, we live on a Goldilocks planet — not too hot, not too cold — still, in spite of the worrying temperatures we're seeing.

Yet the Earth has gone through climates in the past that were outside our current Goldilocks state when CO2 was higher, even much higher, and the planet was warmer, and life still flourished. So explain.

That's absolutely true. If we go far enough back in time — 100 million years ago, when we're in the middle of the Cretaceous period, dinosaurs are roaming the planet, the polar regions of the planet, no ice — carbon dioxide levels were several times higher than they are today.

And those carbon dioxide levels built up over time through very slow but steady volcanic outgassing over tens of millions of years [to] raise the concentration of CO2 in the atmosphere.

And then you have plate tectonics, and how that impacts what we call the chemical weathering, the rise of the Himalayas, which created rising air currents and more rainfall, which scours carbon dioxide from the atmosphere, and it actually becomes dissolved in rocks and streams, runs off into the ocean, [and] gets buried in the ocean bottom.

These processes play out over tens of millions of years, and they regulate the amount of carbon dioxide in the atmosphere: volcanic outgassing puts it into the atmosphere, these natural weathering processes take it back out, and there's a long term balance. But that balance can shift.

And so carbon dioxide levels actually increased for tens of millions of years, until they reached those very high levels in the early and mid Cretaceous.

And then they started to come back down, because those natural weathering processes started to outcompete the volcanic outgassing, which slowed down a little bit, and carbon dioxide levels came down. As carbon came out of the atmosphere, it got buried beneath the surface.

Those processes play out over tens of millions of years — we're talking about 100 million years since the mid Cretaceous — and carbon dioxide levels did come down over that time period, to pre-industrial modern levels. That's a large change in carbon dioxide concentrations, but it happened over 100 million years.

And what we're doing now is we're essentially unburying all of that carbon that nature had buried in the ocean bottom, beneath the surface of the earth, over 100 million years, and we're putting it back into the atmosphere on a time frame of about 100 years, a million times faster.

And that's the difference: we are creating rates of change that have no precedent as far back as we can go.

And if we get into a discussion of the PETM, there was this natural warming period about 56 million years ago, that is our best example of an analog for rapid warming in the paleo climate record.

But when we talk about rapid there, we're talking about a warming of four or five degrees Celsius (7 to 9 degrees Fahrenheit) that happened over tens of thousands of years. We're now warming the planet, once again, over a timeframe of 100 years. So even our best example of a rapid climate change event and a natural rapid climate change event was 100 times slower than what we're doing today.

The Gaia and Medea Effects

And that is terrifying. Now, you also write that the study of Earth's history betrays some climate resilience. What is climate resilience? And fold into that answer the two models of the Earth called Gaia, which posits a kind of self correcting thermostat for the planet, and Medea, which posits feedback loops that lead to runaway states like snowball Earth.

It's really a fascinating topic. You could write a whole book on just Gaia and the faint early sun paradox. The historical characters who are involved are just amazing: Lynn Margulis, Carl Sagan, James Lovelock. It's just a fascinating scientific story that goes back decades and involves some of the most significant players in all of planetary and Earth science.

What I tried to do is to distill the essential message from those past episodes. It was the great Carl Sagan who first brought this paradox to the fore: early on in Earth's evolution, let's say 4 billion years ago, when life first emerged in the oceans, microbes first emerged, the initial emergence of life, somewhere between 3.8 and 4 billion years ago. So, you know, the oceans couldn't have been frozen, because we know they were teeming with life. And so we had liquid oceans with a sun that was 30% dimmer, because the sun has gradually gotten brighter over time.

And if you do the calculations, you assume, say, a modern greenhouse effect, you come up with the answer that the Earth should have been a frozen ice ball, but it wasn't. The oceans were teeming with life, as I said, and what Sagan recognized is that there had to be a substantially higher greenhouse effect at that time.

And it turns out, we now know there was. There was more carbon dioxide, which, you know, is the greenhouse gas that's — obviously, there's a natural amount of carbon dioxide in the atmosphere — but we're increasing it through fossil fuel burning.

So there was, of course, carbon dioxide, but the early Earth was an oxygen free environment. There was no oxygen in the atmosphere. And that means that methane could build up in much higher amounts.

Methane today gets fairly readily oxidized by by oxygen. So it doesn't last very long in the atmosphere. But back then, methane could persist. So there were large amounts of methane as well as CO2. And that made the early Earth much warmer.

The sun got brighter over time. And as the sun got brighter, the greenhouse effect slowly got lower, in such a way as to keep the temperature of the planet within bounds that are habitable for life.

Is it a coincidence? Is it a coincidence that there are these restoring mechanisms as the sun was getting brighter and tending to warm the planet; that warming led to a more energetic hydrological cycle, more evaporation and precipitation; which again, [as] we talked about earlier, scours carbon dioxide from the atmosphere, and forms rocks that dissolve in streams and go off to the ocean. It's nature's way of cooling the planet back down.

And is it just a coincidence? Well, that's where the Gaia hypothesis comes in. And that was first formulated by James Lovelock, and Lynn Margulis, a great scientist in her own right, who was actually Carl Sagan's life partner at the time.

And there are just a number of things that to me are very fascinating about Lynn Margulis. I don't think she ever really got the recognition that she deserved. She was one of the few scientists in modern history that you can name who contributed not just one, but two paradigm-shattering discoveries.

One of those was the Gaia hypothesis, which is proven to be valid, in my view.

The other was the process of endosymbiosis, that bacteria that resembled what today is the mitochondria in our cells. It's the engine that metabolizes oxygen and generates energy. That was a self standing organism that got ingested into another unicellular organism. And that became a symbiotic relationship that persists today. There are mitochondria in every one of our cells that are the power stations of our cells. The chloroplast that is found in plant cells, that allows plants to photosynthesize, was once a self standing organism.

I could go on, as you can see, we could spend an hour talking [about this]. It's just remarkable all of the things that come together here.

But the bottom line is that the Gaia hypothesis is proven valid, that there are mechanisms — and it isn't that there were the teleological interpretations that somehow the Gaia hypothesis was implying that Earth is a sentient organism. That's not what Lovelock and Mergulis were saying.

What they were saying was, it just so happens that the physics, the chemistry and the biology of the Earth system, in a sense, conspire in such a way that life acts to keep the planet within bounds that are habitable for life.

For example, through the role that plants play in photosynthesis, and the global carbon cycle, life itself helps regulate our planetary environment in such a way as to support those restorative processes that keep the temperature within, again, habitable bounds. That's the Gaia hypothesis.

But there are certainly exceptions where that was not the case. And that's what fed the so called Medea hypothesis, this alternative hypothesis. Medea was the tragic Greek figure who killed her own children. And so the Medea hypothesis posits that life can act in a way that, in fact, is perilous to life itself.

The ultimate example of that is the great oxidation event that occurred about 2.8 billion years ago, when you had this rapid emergence and growth of photosynthetic bacteria that metabolize oxygen. It's the modern pathway that plants use today for photosynthesis.

That emerged, that innovation to take CO2 and process it and produce oxygen metabolism. Around 2.8 billion years ago, there was this rapid increase in oxygen in the atmosphere because of these oxygen-generating cyanobacteria. That rapid increase in oxygen scavenged the methane, which could now be readily oxidized. And so it basically removed all of that early atmosphere methane that had been keeping the planet as warm as it was with a fainter sun.

And temperatures dropped and ice formed. And as ice forms, it reflects more sunlight. It's a positive feedback, a self-amplifying mechanism — just the opposite of Gaia, which is restorative.

This is an amplifying mechanism. It's a destabilizing mechanism. And so it cools more. You form more ice and you get this cycle of colder and icier conditions, a runaway episode of global cooling. And we know from the geology, it really happened. Earth became encased, essentially, in a shell of ice, a frozen Earth.

So that nearly killed off all life on the planet. How did life make it through? It's been suggested that there were probably some refugia, places where life could retreat to, deep hydrothermal vents in the ocean, or maybe shallow pools of meltwater sitting on top of the frozen tropical oceans, where life persisted and just barely made it through.

So the lesson here is, yes, life can act in a way that is restorative, that gives resilience to the Earth system, but it can act in the other way as well. And we have to ask, which of those forces are we today? Which do we want to be? Do we want to be the stabilizing Gaia force, or do we want to be the destabilizing Medea force?

The difference between us and those photosynthetic bacteria is that we have agency. We understand our plight, and we can do something about it.

New Science: The Zero Emissions Commitment

And that is exactly the stark choice that we face, although it's not quite as simple as that, because there is some more resiliency than even I expected. I was just absolutely stunned and hope appeared again in my mind when I've heard you say, and I read it again in this book, that once we stop greenhouse gas pollution, the Earth's temperature will stabilize. In other words, we don't have warming baked in, but we do have sea level rise baked in. So explain how these two things work, stabilized temperatures and continued sea level rise.

So that is one of the more important developments in climate science over the last decade or so, the recognition and the refinement of what we call the Zero Emissions Commitment or the ZEC: the question, if we stop adding carbon pollution to the atmosphere, how much additional warming will we still get?

And we used to think that it could be substantial, maybe a half a degree Celsius, a degree Fahrenheit, even after we stopped carbon pollution, because of what we call the thermal inertia. The oceans are very sluggish, they tend to heat up slowly and continue to heat up even after you stop turning up the greenhouse dial, if you will.

And that's true, that is a real phenomenon. But what the models weren't capturing then was an essentially equal and opposite mechanism, which we sometimes call the carbon cycle commitment. And that turns out to be a negative commitment. So you get additional warming from the physical inertia, but you actually get cooling from the carbon cycle inertia.

What am I talking about? Well, when we turn off the carbon emissions, when carbon dioxide stops accumulating in the atmosphere, it actually drops, because in particular the oceans are pulling carbon out of the atmosphere. We've stopped adding it, and the oceans are pulling it out of the atmosphere, so CO2 levels actually drop, and the greenhouse effect slowly decreases.

And so those two different factors, the positive warming effect of physical inertia, and this cooling effect of the carbon cycle, the two things essentially cancel, and you get near as we can estimate, zero additional warming. So when we stop adding carbon pollution to the atmosphere, the surface of the planet stops warming up.

Now, there are some complications here, as you allude to. It is still true that the oceans are continuing to warm up below the surface, because of that thermal inertia effect that we talked about. And as the oceans continue to warm up, they continue to erode the ice shelves in the Southern Ocean that prop up the Greenland [and] the Antarctic ice sheet.

And ice sheets themselves have quite a bit of inertia. They tend to respond slowly and add a lag to the warming that we have caused. And so the ice sheets will continue most likely to lose ice for decades and even centuries after the surface warming stops. And that means that sea level rise will continue long after the surface warming stops.

And so we have to recognize that even in the best case scenario, we are going to have to adapt substantially to the changes that are in store in our global environment. But we can stave off the worst consequences of climate change — the amplification of these extreme weather events, more devastating hurricanes, the extreme heat that we've been encountering, summer after summer — now, all of that stops getting worse when the surface warming stops. And that happens when we bring our carbon emissions to zero.

And so once again, it comes back to this theme that we explored at the beginning of our conversation of urgency and agency. The fact that the surface warming stops when carbon emissions stops means that there's a direct and immediate consequence in our efforts to address the climate crisis.

Drawing Down Atmospheric Carbon: Nature-based or Geoengineering?

That's hopeful. And let me ask you just a quick question. If we can go further and employ things like carbon farming — or many different ways of drawing down carbon from the atmosphere — could we actually start adding to the ice again?

It's a great question…Bill McKibben, who started a whole movement, 350.org — which refers to the concentration of CO2 in the atmosphere. It was 350, 350 parts per million, I think, back when I was in high school or starting college, and now it's close to 420.

And, you know, we said that we can stop continued warming by bringing carbon emissions to zero, but surface temperatures will still stay elevated, basically at their current level for decades in that scenario.

And that means that we will be dealing with the already heightened risk and threats that we're facing today. We're going to be stuck with these devastating extreme weather events in particular. We're going to have to cope with far more challenging climate impacts.

And that's already in a world where we have more than 8 billion people competing for less food and less water and less space. One can argue that even in the current climate, if it stays as it is, just the aggravating effects of climate change really present a challenge to at least the flourishing of human civilization as we know it.

There are very compelling studies that tell us that we have the technology now to decarbonize our world, to decarbonize the global economy…So beware of bad actors, trying to deflect the conversation towards carbon capture and sequestration, to take our eyes collectively off the ball, which is: we need to stop burning fossil fuels and no other schemes or mechanisms are going to change that.

And so the argument goes that, just stopping carbon pollution isn't enough, we're going to have to bring carbon dioxide levels down substantially, back to the levels that they were when I started college, 350 parts per million, if we are to reduce the exposure that we already have to the devastating consequences of climate change.

And there's technology, there are natural climate solutions, as you allude to: restorative agriculture, nature based solutions, reforestation, afforestation. All of those things can help draw down carbon. There may be technology that will be scalable and meaningful at a global scale to capture and sequester carbon.

And so all of those should be on the table when it comes to the longer term challenge we face. What we have to be very careful about are the bad actors today, representing the fossil fuel industry, saying that those are the solutions to the problem; that somehow we don't have to get off fossil fuels, we just need to engage in massive geoengineering, massive carbon capture and sequestration.

Those things are not scalable today. We don't have technology that can be deployed at scale to do that today. And so that's something that's decades down the road. We've got to reduce carbon emissions by 50% this decade, and bring them down to zero by the middle of this century, if we are to prevent three degree Fahrenheit warming of the planet where we'll really start to see far worse consequences. And so the only way we're going to do that is by using the existing technology that we have, and it is adequate.

There are very compelling studies that tell us that we have the technology now to decarbonize our world, to decarbonize the global economy. The obstacles aren't physical, they're not technological. They're entirely political at this point.

So beware of bad actors, trying to deflect the conversation towards carbon capture and sequestration, to take our eyes collectively off the ball, which is we need to stop burning fossil fuels and no other schemes or mechanisms are going to change that.

The only real solution to this problem is reducing fossil fuel burning and the generation of carbon pollution today.

And I've actually heard that we have the technology to go 100% fossil free by 2030, if we had that political will.

Can We Keep Temperature Rise Under The 1.5 Degree C. Threshold?

Michael Mann, I also would like to ask you about this 1.5 degree centigrade limit. You know, the Paris Agreement has said that we need to keep global temperatures from rising more than 1.5 degrees centigrade to avoid catastrophic climate change. And I think it was Jim Hansen who said recently, we've blown past that, we're not going to make it. You have a more nuanced view of this target. Could you explain?

Sure. And I have the utmost respect for Jim; he's really one of my personal heroes. He was the first scientist to speak out publicly about the climate threat back in the 1980s, when most scientists weren't willing to say that human caused warming is here. He delivered very powerful testimony in Congress, alerting the world to the reality that we now face and has spent decades trying to communicate the science and its implications to the public and has contributed substantially to ongoing climate science.

That having been said, I have to politely part ways with him on this. He recently published an article where he argues that there's substantial warming in the pipeline; no matter what we do, it's impossible now to avoid 1.5 Celsius warming.

And he actually advocates for geoengineering, which I think is a dangerous prescription. And it's the sort of thing that people start talking about when they get desperate. If we really believe it's too late to solve this problem the safe way, we start becoming less risk averse and toying with the ideas like manipulating the global environment in some other way to try to offset human-caused warming.

I personally think that geoengineering is a very scary prospect. We could potentially cause far worse problems by engaging in that. And it provides a crutch, right? This idea that we can just engineer our way out of the problem. The fossil fuel industry loves that sort of talk because it's sort of a license to continue to pollute, as far as they're concerned.

So the science, in my view, doesn't support what Jim claims in that paper.

And there's another paper that was published at about the same time in Frontiers of Science. I wrote a commentary in Frontiers of Science that accompanied it. It was about that zero emissions commitment that I was talking about before. And it reaffirms the fact that the warming will stop when carbon emissions reach zero.

Now, one of the things Jim says — well, first of all, the scenario that he explores is one in which CO2 concentrations are maintained at current levels. And we know that's not what happens. The CO2 levels actually come down because of that ocean absorption. And so my view, the whole experimental setup that Jim uses here is a bit of a red herring. It bakes in the wrong answer, that surface temperatures continue to increase because it's not accounting for the absorption of CO2 by the oceans.

But the other thing that he talks about is the aerosol burden: that when we stop burning coal, we stop generating sulfur pollution that has actually had a cooling effect, which has masked some of the greenhouse warming. Sulfur dioxide forms small particulates we call aerosols in the atmosphere that are reflective, and they reflect sunlight back to space. So they're a cooling effect.

And the argument is, when we stop burning coal, when we stop generating that sulfur pollution, the aerosol pollution disappears and we get that extra warming that had been masked by the aerosols.

That is true, but it turns out that that it's a more minor factor today than it was, say, back in the 70s and 80s, because we passed the Clean Air Acts. And we now require coal-fired power plants in the US and Europe and elsewhere to use scrubbers that capture the sulfur dioxide before it gets into the atmosphere.

Some countries like China are still engaging in dirty coal burning, and so in India as well. And so that is part of the picture. But it's also true that that'll be offset: there'll be less black carbon particulates in the atmosphere, which are also generated from coal burning, and those have a warming effect. And if we bring down other greenhouse gases like ozone and methane, all of that extra stuff sort of cancels out.

What we're left with in the end is what we started with, the carbon dioxide. It's all in the end about the carbon dioxide.

And so I disagree with Jim. I would go further. The scientific community, by and large, disagrees with Jim. He takes on the Intergovernmental Panel on Climate Change. He's dismissive of the IPCC. Well, the IPCC is the global community of climate scientists and [it] produces these assessment reports every five to six years that characterize the collective state of understanding, the consensus of the world's scientists. And to be very clear here, Jim is parting way with the scientific consensus.

Now, we should be wary of dismissing James Hansen, even when he departs from the scientific consensus, because in the past, he's been right about some of these things. But I don't think he's right about this.

Do We Paradoxically Risk A New Ice Age?

So briefly, I'd like to touch on two other issues that you talk about in Our Fragile Moment, Michael Mann. One is the issue of the shutdown of the ocean conveyor belt, the Atlantic meridional overturning circulation. If people remember the movie The Day After Tomorrow, it famously posited an instant ice age as a result. And this, this circulation is slowing down. So I wanted to ask you, where are we now? And what are the dangers?

And then I'm going to ask you about the Arctic methane bomb. But let's get to the Atlantic overturning circulation thing first.

Yeah, it sort of rolls off the tongue, doesn't it? The Atlantic meridional overturning, we call it by its nickname, A-M-O-C, the AMOC. Or sometimes it's called the thermohaline circulation, because it's this overturning circulation of the ocean that's driven by contrasts in temperature and salinity, each of which impact the density of seawater and control this sinking motion that drives the delivery of warm surface waters to the North Atlantic and warms up the higher latitudes of the North Atlantic: parts of Europe, Greenland, Iceland, the Atlantic coast of Canada and New England.

And so this is part of the climate system. It today keeps those regions warmer than they would otherwise be.

And it's driven, again, by the sinking of seawater in the high latitudes of the North Atlantic that drives that overturning ribbon-like current. It sinks at depth and travels south. It rises in equatorial latitudes and travels north at the surface.

And so the surface limb of that ribbon-like current is the warm current we sometimes call the Gulf Stream, although the Gulf Stream really stops after it separates from Cape Hatteras off the North Carolina coast. And it continues on into the North Atlantic as part of what we call the North Atlantic Drift. That's no longer the Gulf Stream because the Gulf Stream is really the part that's driven by wind. And we're talking about the component of that current system that's driven by contrasts in temperature and salinity, hence “thermohaline.”

So that's the science. It's sort of complicated.

And of course, it's caricatured in the movie The Day After Tomorrow, as I am fond of pointing out. Even if that current system collapses, North America isn't going to instantly go into an ice age. That's unrealistic. Jake Gyllenhaal isn't going to win an academic decathlon. That's unrealistic. Sorry, it's a bad joke.

So everything that happens in the film is sort of a Hollywoodized caricature of the science. But there's a grain of truth to it, which is that, not only is there the potential for this current system to slow down — and let's talk about why.

The ice melts — the Greenland ice, the surface melting — that meltwater runs off into the North Atlantic Ocean, and it's fresh water. Fresh water is less dense than salty water. So that creates this lens, this cap of cold, light water at the surface in the polar latitudes of the North Atlantic.

Light water doesn't want to sink. It's the dense water that wants to sink. The saltier it is, the more it wants to sink. The fresher it is, the less it wants to sink.

And so that actually stops the sinking motion in the subpolar North Atlantic that is necessary to drive that overall ribbon-like current that is responsible for the warm surface waters that travel towards Europe and North America and Greenland and Iceland.

And so not only is there the potential for that to happen, we think it's already happening. The observations suggest that the current system is likely already slowing down earlier than models predicted.

Why might that be the case? Well, because we're seeing surface melt from Greenland earlier than we expected. And so you can see how there can be a cascade of these effects. If one thing happens earlier than we expected, it can trigger other things to happen earlier than we expected.

So that fresh water is running off into the North Atlantic. It's already contributing to sea level rise. And it's also freshening the North Atlantic and causing the slowdown of this ocean circulation pattern.

As I said, almost none of the impacts that are depicted in the film are going to come to fruition. We don't get another ice age, even if that current system slows down substantially or collapses. But we will get less warming in parts of the North Atlantic.

You might think that's a good thing. Well, the problem is, that changing ocean current system also inhibits the sort of convection, the turbulent motion in the ocean that brings nutrients up towards the surface where they're used by sea life. And so a collapse of this ocean current system could lead to a dramatic decrease in marine productivity.

In one of the great natural fisheries of the world, the North Atlantic Ocean, that we are so dependent upon for a primary source of protein. And for reasons I'm not going to get into, because it actually has to do with some pretty complicated oceanographic physics, the slowdown of that overturning ocean current system also requires that the sea surface rises along the east coast of North America. So we get even more sea level rise, maybe an extra foot of sea level rise along the east coast of the US from a collapse of the AMOC.

And so it wouldn't be the day after tomorrow, wouldn't be another ice age, wouldn't cause tornado outbreaks that destroy the Hollywood sign or super-cooled plumes of water that instantly freeze people in their tracks. None of that's going to happen, but some bad things could happen.

And it's a reminder that, yes, there are surprises in store in the greenhouse, but they're likely to be unwelcome surprises.

No Permafrost Methane Bomb?

And then to go to a more welcome surprise, you say that there is some indication that the permafrost melt will not create a methane bomb. Is that correct?

It is. And that's one of the reasons I go into the PETM. It's another one of those things that rolls off the tongue, the Paleocene-Eocene Thermal Maximum. (That's the reason we just say the PETM.) It's this episode of rapid warming that happened about 56 million years ago. We call it rapid; it was about a hundred times slower, actually, than the warming we're causing today. But it's our best analog for rapid warming in the past.

And there are climate doomers who insist that we have already triggered a runaway warming cycle because of the release of methane from the permafrost. And it will cause an extinction of humans and all other life on the planet, just like the extinction events that happened in these past natural warming events, like the PETM or further back, the end-Permian extinction, the greatest documented extinction in the history of our planet that happened 250 million years ago. At the end of the Permian period, 90% of all life went extinct.

And the doomers will point to those and they'll say that was driven by runaway methane, just like what's happening today. Both of those things are wrong.

And so what I wanted to document in the book is what really happened in those past events, like the PETM or the end-Permian extinction. And there's no evidence that methane actually contributed substantially to the warming. The warming instead was driven primarily by carbon dioxide.

Now, obviously not fossil fuel generated carbon dioxide, although in the book I do explore a thought experiment. How would we know if there were intelligent organisms that went on a fossil fuel spending spree millions of years ago, like we're doing today? What would be left in the geological record? Can we rule out that that's what happened?

And the spoiler alert? Yes, we can rule out there weren't lizard people burning fossil fuels tens of millions of years ago.

Instead, there were episodes of extreme and very intense, explosive volcanism, volcanic episodes that tapped into carbon rich reservoirs in the solid earth and spewed huge amounts of carbon dioxide into the atmosphere. So it was the CO2 that was behind the warming.

There's nothing that could have been done to stop those CO2 driven warming events. But there is something that can be done to stop the current CO2 driven warming event, because it's not from natural factors like volcanoes; it's from human carbon emissions.

And so I felt it was really important to look at those past episodes to establish what really happened. And when you look at what happened, it reaffirms the role of carbon dioxide. It really is about the carbon dioxide.

And it also reaffirms our climate model. So the same climate models that I'm talking about that tell us that we can avert catastrophic warming of more than three degrees Fahrenheit if we rapidly reduce carbon emissions, those same climate models adequately explain what happened in these past events, which gives us more confidence, not less confidence, that we can follow the guidance that these models are providing. And that guidance, again, communicates this message of urgency and agency.

Well, that is a great place to stop in this just fascinating conversation. Michael Mann, your book is Our Fragile Moment, How Lessons from Earth's Past Can Help Us Survive the Climate Crisis. I have more hope than I've had in a long time that we can do this. Thank you so much.

Thank you. It's a pleasure talking with you, Francesca.

About The Author

Michael Mann is the Presidential Distinguished Professor and Director of the Center for Science, Sustainability and the Media at the University of Pennsylvania. He’s the author of numerous books, including The New Climate War, which we spoke to him about in 2021.

Listen to the full interview with Michael Mann here or here.