Carl Sagan (right) with Armenian astronomer Hrant Tovmassian (center) and other participants at the first international SETI meeting at the Byurakan Observatory in Armenia in 1971.
If, over the course of billions of years of cosmic evolution, some species make it through their Anthropocene into long-term, sustainable versions of civilization, what do they end up with? What do their planets look like? How do these worlds function in terms of their coupled systems of air, water, rock, life, and the new addition of a planet-spanning, technology-intensive, energy-hungry society? These are the questions we care about most, because this is the target we must aim for.
There is a great deal of wishful thinking involved when the terms planetary and sustainability are parked next to each other. These are visions of “green utopias,” with sleek, electric-powered trains gliding into elegant eco-cities of vertical farms and buildings mimicking natural forms. While it’s easy to imagine what a single sustainable city might look like, imagining a sustainable planet is another thing entirely. Cities have always been the domains of human control. They are spaces our project of civilization carves out of nature. A planet, however, is a different beast.1
Planets are their own masters. That’s what the astrobiological perspective shows us. The processes shaping worlds are powerful, complex, and subtle. Planets channel vast energies through ever more refined networks of cause and effect. These networks are embodied in winds that pick up fine dust grains and carry them across thousands of miles, or chemical compounds blown into the air by volcanoes, only to end up, millions of years later, embedded in rocks lying deep beneath oceans. Add life to the mix, and planets become almost infinitely more complex, as the planetary systems can now include a coevolving biosphere.
So, how does a healthy planet with a healthy, long-term project of civilization work? To answer this question, we must take our investigation to the final level. Crossing to the safety of a fully sustainable project of civilization on Earth requires not just thinking like a planet, but understanding the profound consequences of planets that have themselves learned to think through their civilizations. What, in other words, does it mean for a planet as a whole to wake up?
THE RUSSIAN MEETING
Ten years after their famous encounter at Green Bank, Frank Drake, Carl Sagan, and two other members of the original meeting found themselves together again. This time, the setting wasn’t the forests of West Virginia, but a mountain in Armenia. Drake and his compatriots, along with a squad of Russian scientists, had come to the Byurakan Observatory for the first true intraplanetary (or international) meeting on interplanetary civilizations.2 While Green Bank had been an intimate affair, with just nine members, the 1971 Byurakan Observatory meeting had more than forty participants, including luminaries from both the Soviet and American scientific establishments. There were Nobel laureates like Francis Crick (co-discoverer of DNA) and Charles Townes (inventor of the laser). Other notables included artificial-intelligence pioneer Marvin Minsky and Canadian neurophysiologist David Hubel, who would go on to win a Nobel Prize for his brain studies.3
Carl Sagan played a central role in organizing the Byurakan meeting. At the height of the Cold War, Sagan understood the symbolic value of an international conference devoted to our place among other, hopefully more mature, civilizations. Getting the meeting placed in the Soviet Union, the United States’ bitter enemy, had been no small task, however. To pull it off, Sagan needed a partner on the Russian side who was just as charismatic and passionate about life in the universe as he was. He found that counterpart in Nikolai Semenovich Kardashev.
Carl Sagan (right) with Armenian astronomer Hrant Tovmassian (center) and other participants at the first international SETI meeting at the Byurakan Observatory in Armenia in 1971.
Just a year and a half older than Sagan, Kardashev was a radio astronomer who had already made important contributions to the study of galaxies and the interstellar medium.4 He had been the force behind the first Soviet search for exo-civilizations, carried out just a few years after Project Ozma. He’d also led the Soviets’ first internal SETI conference in 1964, a few years after the Green Bank meeting. The report he had written on that meeting established his international reputation as a leading thinker about life and the evolution of other worlds.
In that paper, Kardashev laid out a scheme for the technological progress of exo-civilizations. His ideas played an important role in the Byurakan meeting, where freewheeling discussions of the long-term fate of civilizations went on until the small hours of the night. But the impact of what came to be called the Kardashev scale would last beyond the Byurakan meeting and would, in its way, prove to be as enduring as the Drake equation.5
THE KARDASHEV SCALE
When Nikolai Kardashev proposed his scale for measuring the progress of civilizations, he was primarily interested in finding them. Kardashev’s question can be rephrased in a straightforward way: What are the milestones that mark a civilization’s advancement up the ladder of technological sophistication? The basic idea that civilizations evolve through distinct, quantifiable stages as they progress offered Kardashev a lever to lift the discussion about exo-civilizations above pure speculation by providing a means to quantify their advancement. While his main interest was finding radio signals from exo-civilizations, his scale gave us a way to think about their evolution. But within the Kardashev scale lay an essential and mistaken bias concerning the relationship between civilizations and their host planets. Correcting that bias is an essential step in finding a wise astrobiology-based path through the Anthropocene.
Kardashev based his classification scheme on the energy a civilization had at its disposal. The scale had three levels.
•Type 1: These civilizations can harvest the entire energy resources of their home planet. In practice, this means capturing all the light energy that falls on the world from its host star, since stellar energy will likely be the largest source available on a habitable-zone planet. The Earth receives the equivalent of thousands of atomic bombs’ worth of energy from the Sun every second.6 A Type 1 species would have all this power at its disposal for civilization building.
•Type 2: These civilizations can harvest the entire energy resources of their home stars. The total output of the Sun every second is a billion times larger than the sunlight that falls just on Earth. The physicist Freeman Dyson anticipated some of Kardashev’s thinking in a paper written in 1960, in which he imagined an advanced civilization constructing a vast sphere around its star.7 This solar system–sized machine would capture stellar light energy, perhaps via an inner surface covered in solar cells. Such “Dyson spheres” became the archetype for scientists imagining how a Kardashev Type 2 civilization would go about its energy-harvesting business.
•Type 3: These civilizations harvest the entire energy resources of their home galaxy. A typical galaxy contains a few hundred billion stars. Perhaps Type 3 civilizations envelop all their galaxy’s stars within Dyson spheres, or perhaps they have even more exotic technologies at their disposal.
The Kardashev scale represents the scientific imagination working at the grandest, and therefore most mythic, scale. A single Dyson sphere would be a machine of staggering capacity and size. The inner surface of a Dyson sphere built around the sun, with a radius the size of Earth’s orbit, would cover more than ten thousand trillion square miles (the equivalent of almost a billion Earths). Building a machine of this size would require grinding up whole planets for construction materials. We won’t be building one of these anytime soon. Dyson spheres are truly the stuff of science fiction.
But by focusing on stellar-energy capture as the yardstick for a civilization’s evolution, Kardashev’s science fiction–sounding evolutionary scheme could be set firmly in the real world of real physics. That is what gave the Kardashev scale its reach, and why it has endured. For example, a number of researchers, such as Jason Wright at Penn State University, have conducted astronomical searches for the radiation signatures of Type 2 civilizations via their Dyson spheres.8 Thus, as astronomer Milan M. Cirkovic wrote in 2015, “Kardashev’s scale remains the most popular and cited tool for thinking about advanced extraterrestrial civilization.”9
A large part of the appeal of the Kardashev scale lies in its combination of science and mythic-scale optimism via a technologically coherent road map for the progress of civilizations. Its implications are undeniably hopeful. If we continue to advance as a technology-building species, we should naturally pass through each Kardashev type on our way to a future of unimaginable power and reach. A civilization that could build a Dyson sphere would be the equivalent of technological demigods to us. In physics, power is defined as energy used per time. Since the Kardashev scale is explicitly based on energy use, the links between a civilization’s physical power and its metaphorical power—between the science and the mythic—are baked into the scale’s application. Make it far enough, the scale tells us, and you will become as the gods.
More than one author has tried to calculate where on the Kardashev scale human civilization falls today. In 1976, Carl Sagan suggested a way of calculating “fractional” values of Kardashev status based on world energy production.10 In Sagan’s calculation, we end up at about Type 0.7. Freeman Dyson went further, suggesting that human civilization will reach full Type 1 status in approximately two hundred years (with Type 2 requiring another hundred thousand to one million years).11
That sounds pretty good. In just a couple of centuries, we are going to become a true Type 1 cosmic civilization. The problem, of course, is that we may never get there. Our project of civilization has a bottleneck to navigate right now, and our progress through it is anything but assured.
The Kardashev scale originated from a particular historical moment in thinking about exo-civilizations. Like Sagan and Drake, Kardashev was raised on a techno-utopian vision of the future. Technology was imagined in terms of sleek, gleaming machines that were destined to be humanity’s salvation. We could expect that technology’s growth and power would be unconstrained. That was why the Kardashev scale focused solely on energy. Civilizations were expected to rise up the ladder of energy harvesting to ever-greater heights until the entire galaxy would become a resource to be mined. And at each stage (each Kardashev type), the feedback from all this energy use on the physical systems from which the energy was drawn could be ignored. Planets, stars, and galaxies would all simply be brought to heel.
While it is possible that stars and galaxies might not care what you do with their energy, planets are another story. That is the painful lesson of the Anthropocene.
The engineering of entire solar systems or galaxies is so far into the realm of speculation that it’s impossible to know what challenges it will require. But for planets—the focus of Type 1 civilizations—we already understand enough to see how the Kardashev scale represents a kind of planetary brutalism. It inherits a vision of advanced civilizations living in perfect, world-girdling cities where nature is fully controlled. Science fiction is full of this kind of thing. There is Trantor, the home world of the galactic empire in Isaac Asimov’s classic Foundation trilogy. Trantor’s surface lies hundreds of miles below the many shells of machinery that make up its single planet-scale city.12 A more recent example is Coruscant, the home world of the galactic republic in Star Wars, with its continuous stream of “air cars” traveling amid the city’s towering spires. These are visions of planets conquered by the mighty energy-wielding capacities of their civilizations.
But in the years since Kardashev proposed his classification system, we have learned the hard way that planetary biospheres are not so easily ignored. From the work of Lovelock, Margulis, and others, a new scientific understanding of planets and life emerged. Even when they lack life, we now know planets are complex systems. And if a vibrant biosphere is present, it becomes part of that complex whole. The living and non-living parts of the system coevolve across time. In this way, the coupled systems that make up a planet have their own internal dynamics—their own logic. That logic must be fully embraced when mapping out the trajectories of civilizations, as Kardashev hoped to do.
Once again, we are forced to stop seeing civilizations like our own as standing apart from the world that gave them birth. All civilizations, including those that might occur on other worlds, are expressions of their planet’s evolutionary history. From this perspective, our project of civilization is just one consequence of the Earth’s history, not its future master. Every civilization must be seen as a new form of biospheric activity arising within a planet’s history of transformation and evolutionary innovation.
So it is not simply energy consumption (the focus of the Kardashev scale) that must be considered. Instead, we must learn to think in terms of energy transformations. We need to look at those physical laws that constrain energy as it flows through a planetary system. This means we must take a fully thermodynamic perspective as we follow the energy of sunlight being turned into the energy of rising air columns, which turns into the energy of falling rain, and so on, all the way to the energy of living cells.
Recognizing the limits on energy transformation is the fundamental lesson of the Anthropocene. You can’t just bring a planet to heel, meaning you can’t use energy to build a civilization without expecting feedback. Instead, we must begin with a richer understanding of biospheres and civilizations as part of the coupled planetary systems. That means a new kind of map for how civilizations rise to the Type 1 stage and, possibly, survive long enough to become something more. The development of long-term, sustainable versions of an energy-intensive civilization must be seen on a continuum of interactions between life and its host planet.
Sustainable civilizations don’t “rise above” the biosphere, but must, in some way, enter into a long, cooperative relationship with their coupled planetary systems. But what does that look like?
EARTH AS A HYBRID PLANET
Planets are nature’s way of turning starlight into something interesting. The evolution of a planet across billions of years depends on which processes it can harness to absorb starlight and, by doing work, transform that energy into something else. From rainstorms to forests to civilizations, the story of planetary evolution across cosmic time is the story of these energy transformations.
Energy flows are the domain of thermodynamics. The engine in your car is a thermodynamic system. It’s a “heat engine.” Gasoline gets ignited in the cylinders, converting chemical molecular-bond energy into hot gas, or heat energy. The hot, expanding gas pushes on the pistons, converting heat into motion via kinetic energy. The motion of the pistons gets transferred though the gears into the motion of the wheels.
So, it’s not just the energy in the gas tank that matters. It’s the transformation of that energy from chemical form into kinetic form that you need to pay attention to. Some of that original chemical energy gets dissipated (meaning it’s lost and can’t help in doing the work of moving the car) through the heating of the engine block or the friction of the tires on the road.
The science of thermodynamics tells us about the limits of those transformations. It tells us that not all the initial energy (contained in the fuel in the gas tank, for example) can be used to do useful work. Some of it, by necessity, must turn into “waste.” Nature has built these limitations into the universe through the laws of thermodynamics.13 That is why thermodynamics is the right way to think about planets and civilizations and their combined fate.
For a planet with no atmosphere, like Mercury, the available energy transformations are pretty limited. Sunlight hits Mercury’s surface. The surface warms up and emits heat radiation back into space. Once the planet’s surface reaches its equilibrium temperature, there is not a whole lot more to the story, which is why Mercury has looked pretty much the same from one day to the next for the last three billion years or so.14
Add an atmosphere to the planet, however, and the story gets a lot more interesting. When sunlight warms the surface of a planet with an atmosphere, the air near the ground is also warmed. Then the air rises, creating large-scale “convective” circulation. Atmospheric gas rises, and then cools and falls back toward the surface to start the circulation over again. Atmospheric convection is a kind of planetary heat engine, converting sunlight into motion.
If the atmosphere also includes molecules like water, CO2, and other “volatiles,” then evaporation and condensation can occur in the circulation.15 Water, for example, will evaporate near the planet’s surface, turning into a gas that rises with the rest of the air. When the air cools at higher altitudes, the water condenses back into a liquid (in the form of droplets). This is how interesting things like rain or snow can occur—things that could not happen on an airless world.
Just these ingredients—an atmosphere with stuff that can evaporate and condense—are enough to give a planet climate and weather. It’s why even a relatively “dead” world like Mars can still look different from one day to the next, as dust storms, fog, or frost roll in and out.
The presence of liquids flowing across the surface, in the form of rain runoff and rivers, adds a new layer of “interesting,” as the strong weathering of rocks can begin. Elements once locked up in minerals get exchanged with the air and the surface liquids, launching “cycles” of these materials between the planetary systems.16 The branching pathways of these cycles and their feedbacks bestow a new richness to the planet, allowing it to evolve in even more complex ways.
The point here is that all of these processes are fundamentally transformations of energy. The presence of an atmosphere turns solar energy into motion energy as air rises and falls. With water or CO2 in the atmosphere, the energy of motion feeds into the energy associated with evaporation and condensation. Weathering and the breaking of chemical bonds in rocks is yet another form of energy transformation. So, even without life, a planet can take its sunlight and use it for ever more complex work, driving change, evolution, and innovation.
Thinking this way about evolution and energy led Marina Alberti, Axel Kleidon, and me to propose a new classification for planets.17 While the Kardashev scale focused on the total energy falling onto a planet, we were interested in what happens to that energy once it gets within a planet. Here, “within” doesn’t mean underneath the surface of a world, but within the coupled planetary systems. What happens when a sun’s energy, in the form of incoming light, feeds through the linked networks of atmosphere, hydrosphere, and so on, including a biosphere?
Unlike Kardashev, our goal in making a new planetary classification scheme was not detection (though it proves useful for this). Instead, we wanted to use the laws of physics, chemistry, and biology on planetary scales to see where planetary evolution might lead. In particular, we wanted to use the planets we already understood to map out the properties of the ones we don’t understand—the planets with sustainable civilizations.
Working together, the three of us saw that the universe’s vast census of planets might be grouped into a spectrum of five main classes.
An airless world like Mercury is a Class 1 planet in our scheme. The transformations of sunlight are simple, and so the degree of work that is done and the complexity generated are limited. Class 1 planets are truly dead worlds.
A world with an atmosphere but no life, like Mars or Venus, is a Class 2 planet. The flow of gases and liquids driven by sunlight represent work being done within the planetary systems. That work can make things happen on a range of time scales, like the daily appearance of fog or the yearly appearance of dust storms.
Class 3 planets are those with what we called a “thin” biosphere. These are worlds where life has gotten started. It’s affecting the rest of the coupled systems, but does not yet dominate these systems. One way to quantify this is to look at what’s called the net productivity of a planet, meaning how much energy its biosphere harvests. Donald Canfield has estimated the net productivity of the Earth’s early Archean biosphere and found that it was a hundred times smaller than today.18 So Earth during the Archean was a Class 3 world. If Mars had life during its wet Noachian period, four billion years ago, then it too might have been a Class 3 world.
Class 4 planets, on the other hand, have been hijacked by life. They have “thick” biospheres that are deep networks of animal, plants, and microbes, all feeding on each other and all feeding back onto the other planetary systems. The existence of our oxygen atmosphere, created in the Great Oxidation Event, tells us that we are living on a biosphere-dominated planet where life plays an outsized role in planetary evolution. So the Earth, before civilization appeared ten thousand years ago, was a Class 4 world.
Our scheme was based on the fact that we had real examples of the first four planetary classes. Through these known worlds, we could understand how solar energy feeds through the planetary systems and drives evolution. That knowledge gave us purchase to see something essential about our hypothesized fifth class: a world hosting a sustainable civilization.
Going from Class 1 to Class 4 worlds, we see an increase in the complexity of their energy flows and transformations. Class 1 worlds could do little in terms of turning solar energy into work and change. Class 4 worlds comprised rich networks of processes channeling solar energy into work and change. From the perspective of thermodynamics, we could see how planets in each successive class had “found” new ways to transform their incident starlight into evolution. On a world without life, this evolution can be rich, but the pathways are constrained purely by physics and chemistry. In a sense, its details are fairly predictable. Once life appears in Classes 3 and 4, biological evolution takes over. Life figures out entirely new ways to do work, yielding new processes that feed back on the rest of the planet.
The relationship between complexity, work, and energy flows gave us a key to understanding what our fifth class of planet might look like. A thick biosphere on a Class 4 world channels more energy into work than a thin biosphere on a Class 3 world, which itself channels more energy into work than on a Class 2 world. That means a planet with a sustainable civilization—a Class 5 world—might be even more adept at wringing work and change out of sunlight. On a Class 5 planet, the biosphere—which now includes a globe-spanning civilization—becomes even more productive than Class 3 and Class 4 worlds. The civilization not only harvests more energy, as Kardashev imagined, but also figures out how to put this energy to work in ways that do not push the planet into dangerous territory. The civilization, as part of the biosphere, adds what philosophers call “agency.” The civilization makes choices with goals in mind. Thus, Class 5 planets have agency-dominated biospheres. The civilization is now deliberately working with the rest of the natural systems to increase the flourishing and productivity of both itself and the biosphere as a whole.
Perhaps the civilization converts its planet’s deserts into productive ecosystems. Such “desert greening,” if done correctly, could stabilize a changing climate. Or it might engineer plants that can both photosynthesize and produce electricity (there are researchers studying this now).19 Or it might cover regions with solar cells in ways that also increase (or at least don’t decrease) the total biospheric productivity and health of the planet. The possibilities are rich, and our study was meant only to suggest the right direction a Class 5 agency-dominated biosphere might take. There is much fruitful work to be done in turning the basic concept of Class 5 worlds into strategies for the future.
So, where does Earth fit into our classification scheme right now? As we enter the Anthropocene, we are clearly leaving the Class 4 state. Our activity and choices are strongly modifying the state of the biosphere and other planetary systems. But we are making these changes without a long-term plan, as planetary scientist David Grinspoon and others have pointed out.20 We are evolving the planet toward something new, but we can’t say if that novel state will include us in the long term. So, Earth at the beginning of the Anthropocene is no longer a Class 4 world but is not yet, and may never be, a Class 5 planet. As of now, it’s a hybrid world. It’s evolving toward something other than it was, and it’s doing so in a way that’s dangerous for our project of civilization.
The key point in developing these five classes of planet was the necessity of putting civilizations back into the context of the biosphere, rather than above it. From this perspective, sustainable civilizations are extensions of the long process of planetary evolution. Biospheres without civilizations are already agents of novelty. From oxygen-producing microbes to grasslands to megafauna (like wooly mammoths), they produce new things that then enter into the web of positive and negative feedbacks on the planetary system as a whole. The great lesson of Lovelock, Margulis, and their Gaia theory was that the biosphere could evolve feedbacks that kept the system stable. A sustainable agency-dominated biosphere should be no different.
After his pioneering work on the biosphere, Vladimir Vernadsky went on to consider the possibility of planets “waking up” via what he called a “noosphere.” Coined from the Greek noos, for intelligence, a noosphere was a shell of thought surrounding the planet. It was the result of a biosphere evolving creatures that could think and develop technology. From geology to life to mind, the emergence of the noosphere was, for Vernadsky, a next stage in planetary evolution.21
Class 5 planets might be seen as worlds that have evolved a noosphere. The pervasive wireless mesh of connections that constitute today’s internet has already been held up as an initial version of a noosphere for Earth. Thus, we might already make out the contours of what a sustainable world will look like. To truly come into a cooperative coevolution with a biosphere, a technological civilization must make technology—the fruit of its collective mind—serve as a web of awareness for the flourishing of both itself and the planet as a whole.
Beyond the Kardashev scale’s focus on energy as the currency of planetary dominance, we now encounter an essential lesson the stars might teach us about our next moves. Planets are engines of innovation. But, from Class 1 to Class 4, those innovations are blind. They are the result of pure chance and pure mechanics—the laws of physics, chemistry, and biological evolution. They do not have an end in mind. There is no teleology.
Recall that one of the loudest criticisms of Gaia theory was that it could be interpreted to imply that life on Earth “wanted” to steer the planet in some direction. It was in response to these criticisms that Gaia morphed into the less controversial Earth systems theory. There, evolution was once again blind. But when a civilization emerges and triggers its own version of the Anthropocene, the age of blindness must come to an end.
In the deepest sense, Class 5 planets would represent the completion of Gaia. They would be worlds where the planet as a whole has an evolutionary direction, a goal. That is what an agency-dominated biosphere means. The civilization, working for its own continued existence, recognizes itself as an expression of the biosphere and chooses a direction.
So, we cannot bring the world to heel. Instead, we must bring it a plan. Our project of civilization must become a way for the planet to think, to decide, and to guide its own future. Thus, we must become the agent by which the Earth wakes up to itself.
THE WAY FORWARD
Ultimately, the problem we face is confronting a twenty-third-century dilemma armed only with a thirteenth-century mind. Our project of civilization has been successful on scales we could not have imagined when we began it ten millennia ago. But with that success has come consequences that will last for centuries.
Across the long history of our project, we didn’t know our true place in the universe and could not, therefore, know our place within the planet’s own evolution. But now, through science, we can see a new truth. The Earth is but one world among trillions, and we are not a one-time story. Now we can—and must—make this our story. We must make it the human story, one that cuts across cultures, nations, and politics.22
We are, most certainly, not the first species that has dramatically changed the Earth’s climate. It has happened before, and we can see how that story played out in the past. Earth is possibly, and even likely, not the first planet that has evolved a civilization. Using all we have learned about planets, we can see how that story, including climate change, might also have played out in the past.
But what the Anthropocene means for the planet, and what it means for us, are different things. If we continue to do nothing about our use of fossil fuels and the other drivers of the Anthropocene, it is more than conceivable that we’ll push the planet into domains that prove difficult for our kind of complex global civilization. If our project of civilization collapses for a time, or even permanently, the Earth will happily move on without us. In that sense, our urgency in dealing with climate change and the Anthropocene has nothing to do with “saving the planet.” Our entry into the Anthropocene shows that our project of civilization has now become its own kind of planetary power. It’s a new story we have to tell about ourselves, and everything now depends on learning and acting upon it.
Across the pages of this book, we’ve assembled this new narrative through smaller stories of that story’s own evolution. We have encountered heroic scientists who took us up to the mountain so that we might see farther. There were Frank Drake, Jill Tarter, and Nikolai Kardashev, who braved the scorn of their colleagues to take the existence of exo-civilization seriously as a topic for scientific inquiry. Through their efforts, we could begin to see life and the stars in a new light. There were explorers like Jack James and Steven Squyers, blasting robots across space to the other worlds in our solar system. Through their work and the studies of researchers like Robert Haberle, we learned the laws of climate and evolution for all planets. Army corpsmen and scientists like Willi Dansgaard braved Camp Century on Greenland’s ice sheet to help us see more deeply into the transitions of Earth’s climate. Then came people like Donald Canfield, who traveled the world to unpack the deep history of our planet and its life. Putting all this together were visionaries like Vladimir Vernadsky, James Lovelock, and Lynn Margulis, who lifted our sights to see how that life can partner with its planet to evolve into something greater, something more. Finding other planets was the job of scientists like Michel Mayor, Bill Borucki, Natalie Batalha, and others. Their work answered a millennia-old question and, in doing so, filled the night sky with a trillion trillion worlds and possibilities. And finally, appearing at almost every turn, there was Carl Sagan. More than almost anyone else, we owe the possibility of this new story to his genius.
Science has given us a new perspective, a new vision, and a new story that can help us find a way forward as we face the challenge of the Anthropocene. But this can only happen if we listen carefully and truly make this new story our own.
It is time to grow up.
The central argument of this book, and one that Carl Sagan already understood, is that humanity and its project of civilization represent a kind of “cosmic teenager.” We are likely just one world among many that has grown a civilization to the point where it has gained power over itself and its planet. But, like a teenager, we lack the maturity to take full responsibility for our ourselves and our future.
Gaining the astrobiological perspective is the first, essential step in our maturation and our ability to face the Anthropocene. It means recognizing that we and our project of civilization are nothing more than the fruit of Earth’s ongoing evolutionary experiments. Any civilization on any planet will be nothing more than an expression of its home world’s creativity. We are no different from those we would call “alien.”
So our focus has to shift. It’s time to leave the tired question, “Did we create climate change?” behind. In its place we must take up our bracing new astrobiological truth: “Of course we changed the climate.” We built a planet-spanning civilization. What else would we expect to happen?
But we should also recognize that creating climate change wasn’t done with malevolence. We are not a plague on the planet. Instead, we are the planet. We are, at least, what the planet is doing right now. But that is no guarantee that we’ll still be what the planet is doing one thousand or ten thousand years from now.
As children of the Earth, we are also children of the stars. If nothing else, the Anthropocene can make that fact as real to us as the shriek of a howling storm, the oppressive heat of a desert landscape, or the cool silence of a deep forest. Through the light of the stars, through what they can teach us about other worlds and the possibilities of other civilizations, we can learn what path through adolescence we must take. And in that way, we can reach our maturity. We can reach our full promise and possibility. We can make the Anthropocene into a new era for both our civilization and the Earth. In the end, our story is not yet written. We stand at a crossroads under the light of the stars, ready to join them or ready to fail. The choice will be our own.