Much has been written about the Anthropocene—a proposed new division of geologic time in which humans are a dominant force for planetary change: When did it begin? How might it unfold? And can we, the supposed masters of Earth, actually use our powers to make our planet a better place?
Understandably, most of the Anthropocene’s literature to date both in the popular press and in peer-reviewed publications has been decidedly Earth-centric. Yet in a series of papers and his 2018 book Light of the Stars: Alien Worlds and the Fate of the Earth, astrophysicist Adam Frank argues that the Anthropocene’s origins and implications are best understood in the context of astrobiology, the study of life in the universe. Climate change and other environmental effects associated with humankind’s global ascendancy, he says, most likely are universal phenomena for any and every technological civilization that emerges somewhere in the cosmos. Which means the most crucial insights governing the Anthropocene may come less from studying the ground beneath our feet and more from turning our gaze to the heavens.
Scientific American spoke with Frank, a professor at the University of Rochester, about the lessons to be learned from speculations about alien civilizations battling climate change. [An edited transcript of the interview follows.]
What motivated you to write this book?
The book was inspired by some frightening conversations I ended up having with climate change denialists in response to my pieces on that topic for National Public Radio and the New York Times. It was terrifying, really, to see how locked into their perspective these people are and to realize there’s this false narrative about climate change, which we’re stuck in. So this was motivated, in part, by my thinking about how to change the discussion.
Over the years what I’ve come to understand is that human-driven climate change is really an astrobiology problem. It’s not a problem of politics. It’s not a problem of businessmen versus environmentalists. We are talking about something much bigger—a planetary transition, which some scientists label as the Anthropocene. Climate change is just one aspect of this new human-dominated period. My argument is that Anthropocenes may be generic from an astrobiological perspective: what we’re experiencing now may be the sort of transition that everybody goes through, throughout the universe. And there are probably some common features to long-lived civilizations and the planets they inhabit.
I really started exploring this in 2014, when I co-authored a paper with Woody Sullivan of the University of Washington that proposed using dynamical systems theory to model some of these planetary transitions. We argued that it’s possible to identify the basic paths that “exocivilizations” might follow and the feedbacks that might occur when they begin altering their planetary climates. In a follow-up paper that I published with several colleagues, we went ahead and actually did some of that modeling.
Why would you have any faith in models examining the behaviors of exocivilizations—something no one has ever seen?
I like to draw a parallel to the Higgs boson. This is a fundamental particle that was “discovered” in 2012, but really you could say it was discovered in 1964. That was when three papers appeared extrapolating from well-understood physics to propose this particle that would wait nearly half a century before actually being seen. The details obviously would have to be filled in by actual data, but in that intervening time physicists went quite far in thoroughly extrapolating the particle’s nature.
Thus, when it comes to thinking about the interactions between an advanced technological civilization and its planet, well, we actually know a lot more about that today than people knew about the Higgs boson 50 years ago. We have lots of examples of planetary climates that we’ve studied right here in the solar system—Venus, Mars, Titan, Jupiter, and so on. And we’ve got computer models that can nicely forecast, for instance, the weather on Mars! So we really do understand climate pretty well. And a civilization, to some degree, is just a mechanism for transforming energy on a planetary surface. This gets us into the realm of thermodynamics on global scales, which is supercool.
As long as we ask the right sort of question—“What is a planet’s response to having this energy dumped into it?”—we have reasonably good “guardrails” that allow us to address it.
But that’s mostly planetary science. What about the social or biological aspects here? How are you modeling that?
Well, just as we understand planetary climates pretty well, we can use the basic, fundamental tenets of life to guide us, too. Organisms are born, some of them reproduce, and they die. Living things consume energy, and they excrete waste. That should be true even if they’re made of silicon or whatever.
The next step is to incorporate principles of population biology, in which the idea of “carrying capacity”—the number of organisms that can be sustainably supported by the local environment—is very important. This approach can also be mathematically applied to the state of a planet. So in our modeling work we’ve got an equation for how the planet is changing and an equation for how the population is changing. What ties them together is the predictable result that as environmental conditions on a planet get worse, the total carrying capacity goes down. A civilization with a population of n will use the resources of its planet to increase n, but at the same time, by using those resources, it tends to degrade the planet’s environment.
In our study, we used these basic ideas to address the question of if, and how, exocivilizations can get through their own versions of the Anthropocene. Our first models were pretty simple but gave us a pretty rich view of the possible trajectories for exocivilizations.
What were the results of your modeling? And do they make you feel optimistic or pessimistic about our own prospects?
In the models, we saw three classes of behaviors, three trajectories: A “die-off,” where the population overshoots the carrying capacity and then dwindles; a “steady state,” where the population growth slows and ends up within the bounds of carrying capacity; and a “collapse,” where the population and the carrying capacity both just drop like a stone.
It’s important to remember we aren’t trying to say any particular history is bound to play out on any particular planet. We are looking at the average properties of “successful” versus “unsuccessful” trajectories for civilizations reaching this Anthropocene-like planetary transition.
The results actually made me feel both optimistic and pessimistic. I was happy to see we did find sustainable steady states—it could’ve turned out that they didn’t exist. So our models predicted that long-term civilization/planet co-evolution is possible. Hooray!
But we also found trajectories where equilibrium could be reached only after 90 percent of your population died off. It’s not even clear that a complex technological civilization could survive losing nine out of every 10 individuals. It might well just descend into chaos.
And there was also a fourth and really chilling trajectory we found. It popped up when we looked at how a civilization might switch from high- to low-impact energy sources—such as switching from fossil fuels to solar power, for instance. In some of those scenarios, where the population is soaring and the planet is heating up, the civilization shifts to the low-impact energy resource, and everything seems to get better at first—but then a collapse occurs anyway. This fourth trajectory is really scary because it suggests you can make all the right choices and still have things not work out.
Why would that happen?
Because planets are complex systems that exhibit nonlinear dynamics. Messing around with a planet’s climate can be like rolling a big rock down a hill. Once the rock really gets going, there’s no turning back, and maybe it just shoots right off a cliff.
The climate is basically a giant planet-sized machine with lots of moving parts—the atmosphere, the lithosphere, the cryosphere, the biosphere—and the interactions among those moving parts may be quite sensitive. So if you push it hard enough, even if you stop pushing it shortly after, there isn’t always a way to recover. That’s one of the big messages of the book. We have to start thinking like a planet. Our view of climate change—the faux political debate—is so narrow because we think we’re the first time this has ever happened. We’re kind of like cosmic teenagers who are stuck in our own immaturity.
So where do you think Earth is in this spectrum of possibilities?
I don’t think anyone knows yet. More work needs to be done—better models with more realistic climates. There has certainly been a lot of discussion in the earth science literature about planetary “tipping points,” the idea that you push too far and, whoops, now you’re tipped over to another state. Clearly, people worry about this. But it’s unclear as to where and what exactly the tipping points are and where we may be relative to them.
But back to the idea of “changing the discussion”—your motivation for writing the book. Surely we could do more with these ideas than just discuss them. Don’t they recommend some action?
Of course, they do—but most of those actions are indistinguishable from ones that follow from lots of other work in climate science and policy.
I really do think, though, that the route to our making it through the Anthropocene runs through other planets. We aren’t going to become a sustainable planetary civilization by only dealing with Earth. I give lots of examples in the book, but one of the best is the fact that the climate models that revealed the possibility of “nuclear winter”—a global cooling caused by the atmospheric effects of a nuclear war—relied heavily on data about Martian dust storms. Talk about cross-fertilization! Those nuclear winter models totally changed the debate about nuclear weapons, and they came from understanding another world.
So we can’t just sit here studying tipping points on Earth at the expense of going out and exploring other worlds and looking for life and intelligence elsewhere, because the knowledge we gain from that is probably essential for our own future. Think of it this way: If you’re sick and go to the doctor to be cured, the doctor will have pretty limited abilities if he has only ever studied [just] you. If he has studied you and lots of other people, [however,] he’ll have a much clearer picture of what ails you. It’s probably like that with planets and civilizations, too.
FOUR SCENARIOS for the fate of technological civilizations and their planets, based on mathematical models developed by Adam Frank and his collaborators. The blue line plots the trajectory of the civilization’s population, and the orange line shows the co-evolving trajectory of the planet’s temperature (a proxy for climate).
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