Scatter, Adapt, and Remember: How Humans Will Survive a Mass Extinction

WE’VE SEEN HOW life-forms like cyano, birds, and mammals made it through mass extinctions, and we’ve explored the strategies humans used to deal with threats to our species. But we’ve also seen a lot of failure modes that consigned whole ecosystems and classes of people to death. How will we convert our guardedly hopeful stories of a human future into a real-life plan for survival that avoids some of the worst failure modes?

We’ll start by changing our cities, which are a powerful expression of human symbolic culture and a perfect example of why we have a lot to learn about adapting mass societies to our environments. Cities have always been central to human civilization, but now they’ve become almost indistinguishable from it. Certainly they’re the sources of our greatest economic, scientific, and artistic productivity. They’re also a good way to organize communities when you’re an invasive species with a population that just passed the 7 billion mark. It’s easier to provide standard levels of good hospital care, sanitation, housing, and education to 1.6 million people packed into the island of Manhattan, for example, than to the less than 1 million spread out over the state of Montana. But cities are also a problem. They’re death traps during pandemics and natural disasters like the 2004 Indian Ocean tsunami. Though cities are efficient in their use of energy, they still use far too much of it—especially given that most of them run exclusively on fossil fuels that are not sustainable and harm the environment.

Still, cities have become the dominant form of human community today. In the past decade, the number of people on Earth living in cities surpassed those living outside of them. And those numbers are expected to rise—the United Nations’ Population Division estimates that 67 percent of humanity will live in urban areas by 2050. Certainly it would be better for people and the planet if we could dramatically decrease our population, as Alan Weisman argues in his book The World Without Us, but that idea simply isn’t pragmatic in the next few decades. It would require us to regulate the bodies of billions of women, leading into a morally gray area from which we might never return. For now, we must accept that our population is growing. And that means human survival in the near term depends on whether we can build cities that protect their masses of inhabitants while also preserving and sustaining the environment. In short, we need cities that don’t collapse at the first twitch of an earthquake, that aren’t hives of disease, and that offer sustainable energy and food sources to their citizens.

To get there, we must first understand how cities work and what makes them survive over the long term.

The City Is a Process

A city is more than its brick and mortar. It is the sum of its cultural history. That’s why the urban planning philosopher Jane Jacobs, in her groundbreaking 1961 book The Death and Life of Great American Cities, makes the case that what attracts people to cities is “sidewalk life.” By that, she means the everyday social world of the city, the comings and goings of neighbors, strangers, and events. The city, Jacobs believed, was profoundly social. People flocked to them for the excitement of new kinds of human interaction, not to admire great works of monumental architecture or simply to make money.

Jacobs’s interpretation is just one of many ways to express a certain ineffable aspect of city life. Some call it an emergent property, a system of organization that arises spontaneously out of chaotically interacting parts. Others call it a cultural legacy. And the fantasy author Fritz Leiber dubbed it “megapolisomancy.” The point is that cities draw their vitality from a mix of social, political, and cultural practices that are hard to quantify scientifically. But they are also undeniably products of technology and engineering. They are financial powerhouses too, fueling their inhabitants’ cultural and scientific undertakings in massive, elaborate marketplaces that link cities to each other across the world.

Successful cities are what physicists might call stochastic, meaning a structured, repetitive process that contains an element of randomness. Certain structures appear in cities again and again. Even the very earliest cities, located in what are today Turkey and Peru, contain monumental architecture in honor of religious and political leaders. They also contain private homes where people lived in family units, cooking, sleeping, and raising children together. And yet every city has its own character, its own random, emergent sensibility that’s a product of a particular group of people at a particular time in history. Some cities, like Istanbul and Paris, manage to nourish this stochastic process over centuries and even millennia. Others, like Detroit, flash brightly for a few decades and then crumble into ghost towns. To make our cities long-lived, shaping them into “battle suits for surviving the future” as the industrial designer Matt Jones calls them, we have to respect their stochastic natures. We must build cities with safe, sustainable structures, but always leave room for randomness and social change.

Anthropologist Monica L. Smith, who researches the development of cities in the ancient world, has noted with some frustration that there is really no good way to define what makes an area “urban.” Key components of urban life include a high population density, specialized forms of work, social stratification, and monument building. But listing the ingredients of a city doesn’t adequately address the problem of definition, because cities are what Smith calls “a process.” The brilliant urban planner Spiro Kostof suggested the same thing, writing that “a city, however perfect its initial shape, is never complete, never at rest.” In other words, a city is always shifting, perhaps possessing some aspects of urban life at one time and other aspects later on. Moreover, what felt urban 5,000 years ago probably wouldn’t feel urban today—and indeed, what feels urban in Canada might not feel urban in China. We may know a city when we see it, but the idea of a city is itself a moving target.

Cities were born in two very different regions of the world: along the coast of Peru in South America, and in the area once known as Mesopotamia, where southern Turkey, Syria, and Iraq stand today. The Peruvian cities, clustered along mountain rivers speeding toward the sea, date back to 3200 BCE. They boasted large sunken plazas surrounded by platforms, winding stairs, and rooms that were probably living quarters. The largest of these cities is believed to be Caral, which dates back to 2800 BCE and may have housed up to 3,000 people who left behind art, carvings, and woven textiles. Most likely, Caral and its outlying cities lived on fishing and agriculture, trading goods and ideas back and forth.

Unlike the cities around Caral, which were elaborately planned around large, central public spaces, the even more ancient city Çatalhöyük, in southern Turkey, looks more like a honeycomb made out of mud. Anthropologists believe it was probably constructed in roughly 7500 BCE, and inhabited for hundreds of years after that. The people of Çatalhöyük built their simple one-room houses right next to each other, with no streets in between. Doors were built into the rooftops, and residents clambered across each other’s roofs and down ladders to reach their pantries and beds. When the mud walls of a Çatalhöyük house began to crumble, residents would just build a new structure on top of the old one. Many ancient cities are called “mounds” because over time, ancient city people literally created hills by building new homes upon the ruins of the old. Anthropologists today often find the remains of these cities by using satellite photos to look for suspiciously symmetrical mounds in regions of the world known for early urban development.

One of the great debates among anthropologists is whether urban life or agricultural life came first. Though we may never know the answer—and it may have varied from region to region—most anthropologists today agree that cities like Caral and Çatalhöyük would have required people to develop highly efficient agriculture. After all, farming is only necessary when there are hundreds or even thousands of hungry mouths to feed in one permanent location. Did the city therefore predate the farm? Tantalizing evidence from a southern Turkish site called Göbekli Tepe, dating from 10,000 BCE—a fascinating circular formation of monuments covered in bizarre human-animal imagery—suggests that the very earliest urban formations were built before evidence of agriculture. Still, it’s possible that humans’ first efforts at crop cultivation would be impossible to distinguish from wild plants, meaning the people who visited Göbekli Tepe might have had small farms that we simply can’t recognize from their remains. Debates aside, what’s certain is that by the time people were living in the extremely ancient cities of Caral and Çatalhöyük, farming was the main occupation of most urbanites. Cities cannot exist without agriculture.

Cities didn’t just change the environment with agriculture; they changed humanity, too. Stanford University anthropologist Ian Hodder, who has led excavations at Çatalhöyük since the early 1990s, believes that cities “socialize” people. Their routines are transformed by what he calls “bodily repetition of practices and routines in the house,” as well as the “construction of memories.” He writes about one house in Çatalhöyük whose residents rebuilt the structure six times over a couple of centuries, each time with exactly the same layout. Like their neighbors, these people shared a religious tradition of burying the bones of their ancestors in the floor of the house. As time passed, the house became more than just a dwelling. It was a monument to previous versions of the house, to the family, and to the city itself. This is a useful way to think about cities in general, and helps illuminate why we attach so much significance to preserving ancient structures in our modern cities. Our cities are monuments to our shared history. Though the bones of our ancestors aren’t literally built into the floors of our homes anymore, they remain there in a symbolic sense. That ineffable megapolisomancy that gives cities their allure comes from the way they are constructed of memories as much as they are constructed from brick and steel.

Cities That Endure

Anthropologist Elizabeth Stone has been excavating ancient cities in the Mesopotamian region, especially Turkey and Iraq, since the early 1980s. When I asked her why some cities manage to survive for thousands of years, she cautioned me that cities don’t ever remain the same over time; they have broken histories, collapsing and rising again. Ancient cities, for example, were organized in a way dramatically unlike cities of today. “If you look at pictures of Baghdad today, you see different districts that are segregated by class. It’s so fundamental that it’s visible from space,” she said. But if you look at the layout of ancient Pompeii, it’s impossible to say where the rich and the poor lived. There is variability between neighborhoods, but there are no visible differences in wealth. As she’s mapped Mesopotamian Era cities, Stone has been struck by how little variability there is in the size of houses. Everybody seems to have homes that are roughly the same dimensions, though some might have more rooms than others.

The differences between ancient and medieval cities are just as stark. The imperialist Rome of antiquity wasn’t the same as the Church-dominated Rome of the Middle Ages. The former glory of the ancient world was reborn as a new city for the medieval world. Medieval city growth moved slowly, often funded by the aristocracy or the church. But starting in the nineteenth century, industrialization pushed city growth into the hands of wealthy entrepreneurs and developers, whose greatest monuments became skyscrapers devoted to various corporate headquarters. This era also witnessed a steep rise in urban populations, culminating in our majority urban population today. And now it’s become a completely different city again. People have always been drawn to Rome because of its dramatic history, but the urban experience during each stage of its life was notably transformed.

Long-lived cities survive by going through periods of collapse and rejuvenation. It’s possible that cities tend to collapse when people have less social and economic mobility. “People at the bottom may retreat into the countryside and leave the sphere that’s controlled by the city,” Stone speculated. As soon as there is more opportunity in the city, peasants return and try to climb the social ladder again. Most cities that last for more than a few hundred years are located at the heart of shifting empires, like Istanbul (formerly Constantinople) or Mexico City (formerly Tenochtitlán). Both cities have been inhabited for centuries, but by peoples from successive, often adversarial political groups. Their fates rise and fall with the empires that claim them. Cities may be built on memory, but they are also processes, always changing.

Longevity isn’t the only measure of a city’s success, however. As Harvard economist Edward Glaeser puts it in his book Triumph of the City: How Our Greatest Invention Makes Us Richer, Smarter, Greener, Healthier, and Happier:

Modern cities survive by offering people a space where they can form social groups that would be impossible outside them. Kostof calls cities “cumulative, generational artifacts that harbor our values as a community and provide us with the setting where we can learn to live together.” The city community’s “values” are part of the urban structure itself. This helps explain why some cities remain politically distinct from their countries, their cultures proving stronger than the culture of their nations. In the last century, West Berlin and Hong Kong found themselves in this situation. Both cities had strong ties to other nations and urban areas, and used those ties to remain relatively democratic cities devoted to capitalist trade, despite being located inside and alongside powerful communist nations. Other examples include cities like New York and Budapest, whose citizens have often defined themselves by being at odds with the countries that contain them. Cities socialize citizens into certain habits of mind, and these can be hard to break. In fact, sometimes a city breaks with its nation rather than breaking away from its own social norms.

Case Study: San Francisco as a City of Tomorrow

How can we ensure that tomorrow’s cities will harbor thriving communities that don’t decay into insignificance like Detroit or disappear into the fog of history like Çatalhöyük? We need to incorporate mutability into urban design. But as we face the future, that mutability must also include ways of building sustainability into the very structure of our cities. Urban geographer Richard Walker believes the San Francisco Bay Area provides a useful template for how that could happen. In his book about San Francisco, The Country in the City, he explains how the Bay Area’s green spaces are as much constructions as the houses and buildings. The region’s designers often built verdant parks on top of barren dunes and scrub, including both “country” and “city” in their plans for how they would convert the wild lands of Northern California into an urban space. The results are visible everywhere in the Bay Area. To get from the BART commuter-train station to Walker’s Berkeley home, I followed a winding path through several public parks full of play equipment and flower beds. Along the way, I passed more bicyclists, pedestrians, and green spaces than I did cars.

Still, the Bay Area isn’t built on environmental principles alone. It’s also a successful region because its residents have consistently been on the cutting edge economically. “Going back to the Gold Rush, San Francisco has always had a big skilled labor force full of young, creative people,” Walker said. “That was true when they were inventing new kinds of mining equipment in the nineteenth century, and it’s true now with financial innovation and retail innovation, as well as electronics and biotech.” The Bay Area’s financial heart is truly in the long, braided terrain of farms, parks, and cities that make up Silicon Valley to the south. They pump cash from the innovative tech and science industries into a region that includes Marin County to the north and Berkeley and Oakland to the east. Today, many young people who are attracted to the culture of San Francisco come to the region to settle in its most famous city. But they commute every day to Silicon Valley in one of hundreds of sleek, Wi-Fi-enabled buses dispatched by Google, Genentech, Apple, and other companies to make commuting easier on their employees—and reduce emissions in the process.

Just as important as its economic success, however, is San Francisco’s status as what Walker called a “wide-open city.” By that, he means a city prepared to tolerate, and even embrace, experimental ideas. In the early twentieth century, the Bay Area was home to the nation’s earliest environmental groups, racially integrated unions, and a large gay community. In this way, San Francisco in the 1920s and ’30s was like Los Angeles and Berlin. But unlike those cities, the Bay Area never suffered a political crackdown on its most rebellious citizens. During the rise of fascism in Berlin, the Nazis drove out (and occasionally murdered) progressives and openly gay activists like the psychologist Magnus Hirschfeld. And in 1950s Los Angeles, the House Un-American Activities Committee persecuted people with leftist sympathies working in Hollywood. Many lost their jobs and had to leave the city. Meanwhile, in San Francisco, the radicalism continued virtually unchecked. Citizens founded environmentalist groups like the Sierra Club, and a general strike in the 1930s brought the city’s bosses to their knees. In the 1960s, an odd set of local environmental groups, industrialists, and politicians came together to battle developers who wanted to top up the bay with landfill so the city could sprawl from the Embarcadero in San Francisco across to Alameda in the east, and all the way down to Redwood City in the south. The environmentalists won that round, and the bay was protected from destruction.

Out of struggles like these arose a city unlike its predecessors, an urban environment that was green almost from its very inception. “The environment in the Bay Area welded many local opposition movements into a larger radical vision of a green city,” Walker explained. “The feeling here wasn’t ‘protect my neighborhood and screw everybody else.’ It was ‘protect my neighborhood and come hike in my green space.’ It was very public-spirited.” By the mid-1960s, the city’s coalition of local green groups had become so powerful that California passed the first of many environmental-protection laws to prevent anyone from ever filling in the bay for development.

In building the Bay Area, urbanites realized that success meant destroying the false division between country and city. But San Francisco is just one example of a city that has changed over time by getting greener. People in many cities, from Tokyo to Copenhagen, want to preserve local environments not just with protection laws, but also with solar power, high-efficiency buildings, and urban farms. Cities of the future are changing to include many aspects of the country within their boundaries.

As we’ll see in the next few chapters, urban planners, architects, and engineers are coming around to the idea that cities must be as much part of their environments as coastlines and trees are. Government and private industry are pumping billions of dollars into the development of energy-efficient buildings, solar power, smart grids, urban gardens, green roofs, and many other eco-technologies. The city of the future, most agree, will be planned the way the Bay Area has been for almost 50 years.

It may seem bizarre for the Bay Area to represent urban life of the future, given that an enormous earthquake or tsunami could wipe out the whole region tomorrow. But as we’ll discover in the next chapter, new engineering techniques could help our cities survive all but the worst natural disasters.

THERE’S ONE THING that never changes when it comes to city life. Disaster will always strike. Whether it’s from storms, floods, earthquakes, fires, or just urban decay that’s turned buildings into deadly hulks of rotting wood, cities fall apart. One of the biggest questions for urban planners and engineers is how to build cities that can withstand common calamities. It turns out the best answer is to destroy a lot of buildings on purpose. Engineers innovate city-building technologies by using enormous labs to re-create the worst disasters you can imagine—and then inventing structures that survive them.

Many of these labs are in remote facilities that you might at first mistake for storage warehouses, missile ranges, or airplane hangars. Several years ago, I crisscrossed the United States, trying to visit as many disaster labs as I could. I started with the Energetic Materials Research and Testing Center, a 40-square-mile swath of blue-veined rocky hills covered in sage brush next door to the White Sands Missile Range in Socorro, New Mexico. Between peaceful hillsides mostly dominated by wildlife, researchers from New Mexico Tech collaborate with government and industry scientists to study how explosions affect city environments. The day I was there, emergency responders set off a car bomb to see whether a specially reinforced brick wall could protect a test dummy from the blast. The dummy survived, though the “control” dummy behind a standard wall was shredded, as was the car. Analysts pored over the crater the car left behind, measuring the distance that the engine had traveled, trying to analyze every factor in the explosion. Other tests at the facility measure the effects of tanker explosions, gunfire, and even tiny suitcase bombs. Their results could help city planners and rescue workers design streets and walls to protect residents from harm.

Tests like these also help rescue workers learn new ways to pull people from wreckage that can be even more dangerous than the blasts that created it. Rescue innovation is a big part of what scientists and emergency responders study at Texas A&M’s Disaster City, another enormous open-air facility devoted to destruction for the sake of survival. Here, engineers can build whole city blocks just to blow them up in a re-creation of a meth-lab explosion or a house fire. They can simulate a train crash or root around for survivors in a collapsed parking structure. When I visited, engineers were testing experimental reconnaissance robots designed to fly or climb around in dangerous, unstable environments to find people trapped in rubble. Next to Disaster City is a fire field with a mock chemical-processing plant. While I watched, the technicians opened the valves on gas lines that fed into a maze of pipes and tanks, emulating what would happen if such a plant caught fire. Firefighters struggled to contain the two-story flames. I stood in the heat-mangled air outside the painted safety lines that bracketed the area like the sidelines on a basketball court.

While these facilities specialize in pyrotechnics, another network of labs in America and Japan are filled with huge machines that can simulate earthquakes and tsunamis. At Oregon State’s tsunami lab, engineers carefully erect scale-model cities around the “shoreline” in a 160-by-87-foot water tank, then create carefully designed tidal waves with huge paddles to see where the water washes ashore. The tank is lined with sensors that measure the movements of tiny beads of glass suspended in the water—this allows researchers to understand how waves propagate through oceans, and better predict how tsunamis will behave when they hit the shore. Sitting high above the tank in a control room, scientists use a computer to control the paddles, generating exactly the kinds of waves they want to send crashing down on the model city. They can imitate the conditions that would affect the speed and shape of a tsunami in a very specific region, such as the northern coast of Oregon or the San Francisco Bay. Ultimately, these tests help city planners determine a safe distance to build from the water, as well as the optimal places to put escape routes in case of flooding.

As scientists in these labs struggle with floods and fires and quakes, they are also struggling with a fundamental contradiction at the heart of city design. As the urban planning historian Spiro Kostof explains, cities are the result of ongoing conflicts between centralized planning and organic, grassroots development. To prevent people from dying in quakes and floods, for example, we need rules about how and where developers are allowed to build. But city governments can’t control everything. City dwellers aren’t going to be happy if they don’t have the freedom to change their living spaces and neighborhoods. Not everyone can afford to build homes that are robust against every kind of possible disaster, either. That’s why engineering a disaster-proof city isn’t about magically conjuring damage-proof structures. Instead, it means building urban areas that will kill the smallest number of people possible during a disaster. This is pragmatic optimism at its most literal.

Inside the Apocalypse Lab

I met the UC Berkeley civil engineer Shakhzod Takhirov inside a three-story warehouse that’s home to UC Berkeley’s Earthquake Simulator Lab. Located in the city of Richmond, the lab is easily identified by its proximity to piles of shattered wood beams, twisted girders, and giant cracked columns of concrete. But this was no junkyard. As I wandered through the rubble, I noticed that every crack and break had been carefully labeled with measurements in permanent marker.

The instruments of destruction that created these piles occupy most of the lab. Towering over my head as I walked in was a 65-foot-tall steel piston that can deliver up to 4 million pounds of compression to whatever structure or material is unlucky enough to be in its grip. Want to simulate traffic load on a bridge support, or the pressures that a skyscraper might deliver to its foundation? This machine can help.

Behind the mega piston, I could see that day’s main experiment. Lab technicians had built a life-sized frame for a single-story building in the middle of the warehouse-sized lab space. Attached to the frame were huge hydraulic motors that looked a bit like pared-down robot arms that were braced between the building and a strong concrete wall. These motors were controlled by researchers in a room packed with computers. With the press of a button, the engineers could deliver small, precise earthquakes to the building—or bone-rattlingly big ones. Sensors on the structure would measure every deformation and shake propagated through it.

Takhirov, who bounced around the control room taking obvious delight in the powerful machines working outside, has always lived with the threat of earthquakes. His birthplace in Uzbekistan is known for its massive quakes, as is the San Francisco Bay Area, where he’s spent much of his adult life. Though he began his career as a mechanical engineer studying wave dynamics, over time he left theory behind and got interested in real-world applications. The day I visited, the researchers were deforming one wall of their building with the motors. The process was slow, involving tiny shifts in the slightly crushed structure, and a great deal of muttering from graduate students about the waveforms we could see undulating across several computer monitors.

There are two ways to simulate earthquakes. Researchers can use a shaking table, which is exactly what it sounds like. They build a structure on top of a platform that can be shaken from underneath, creating an earthquake, so they can watch what happens and learn from it. The second way is what Takhirov’s colleagues and students were doing. They used their giant actuators to imitate how earthquake forces would deform the building, but they were doing it in slow motion. There was none of the violent motion you would see in an earthquake, but those robot arms carried the same force as a quake would. “Essentially we do this so we can look at each step,” Takhirov said. Using their computers, the researchers can also create a “hybrid simulation” that combines a mathematical model of a building with the physical object they’re manipulating in the lab.

The experiment that I was watching with the one-story building turned out to be a model of a two-story building—the second story existed only in software. We know enough about earthquake engineering at this point that we can actually extrapolate how a second story might behave based on what the first story does when it is slowly crushed by giant motors. Hybrid simulations make it easier for engineers to calculate how city buildings might respond in a quake, even if they aren’t able to build an entire 50-story building and wiggle it.

This particular hybrid simulation would ultimately reveal what happens to a multistory building during a quake if the second floor had been “isolated,” or built with a damper—usually a layer of flexible material—between it and the first story. Isolation stops the quake’s motion from propagating through a building unchecked, preventing it from swaying, torquing, and crumbling. Usually isolators are built into the bases of buildings, but the experiments I saw would demonstrate whether isolation units could be helpful between stories, too. If the isolator prevented significant damage in that simulated second story, these researchers would move on to the next phase of their work—getting their engineering discovery implemented in the real world.

How to Prevent Death with Engineering

What Takhirov and his colleagues learn in the Earthquake Simulator Lab gets translated into the building code, a set of safety rules that constrain how structures are built. These codes exist all over the world, varying slightly from region to region. When engineers like Takhirov make a new discovery about earthquake engineering, their next step is to petition to change the rules that govern city development. “I can conduct several tests, and then I can approach the coding committee with my results and say, ‘I should change things here,’” Takhirov said.

Failure to update building codes is a major reason so many lives are lost in cities during disasters. Takhirov visited Haiti soon after the series of quakes that nearly leveled the capital, Port-au-Prince. He and his team documented the damage, using conventional cameras as well as sophisticated laser-imaging devices that produced 3-D representations of the shattered city. A lot of the damage could have been prevented with better engineering. They found buildings that never would have collapsed if they’d used simple reinforcements. Unfortunately, however, the local building code lagged behind recent discoveries. But some buildings weren’t up to the local code, either—mostly because builders couldn’t afford the reinforcements and structural planning required. The more earthquake-proof a building is, the more expensive it gets. That’s why Takhirov tries to be pragmatic about earthquake engineering. When builders have to cut corners, they should always prioritize human safety over a building’s durability. “Sometimes it’s more cost effective to have a building that will be damaged but not collapse,” Takhirov explained. “That way people can escape, even if you have major damage.”

His thoughts turned to what Bay Area residents call the Big One, or the next massive earthquake that could hit the region at pretty much any time. “We must be aware that the Big One will be strong, but I have some confidence that it’s going to be okay, and a minimal number of lives will be lost from collapsed buildings,” Takhirov said. Still, he wasn’t sanguine. “Unfortunately, the Big One is going to happen no matter what,” he said. And then, like a true engineer, he began imagining the discoveries such an event would yield. “When it happens, we will deploy all our cameras, and that will be our next big project.”

Other engineers are more fatalistic than Takhirov about how many lives they can save. One state north of Takhirov’s earthquake-simulation lab, on a hillside in the middle of Oregon’s Willamette National Forest, a U.S. Geological Survey (USGS) engineer named Richard Iverson has created hundreds of landslides to learn more about how these often deadly disasters start. He does his work at the USGS “debris-flow flume,” which is pretty much what it sounds like. It’s an outdoor laboratory that consists of a massive enclosed slide, adorned with cameras and embedded with sensors that measure everything from pressure to sheer force while fast-moving globs of mud, rocks, and water rush down the slope. When I spoke to him, he’d just finished a series of experiments where he and his colleagues sent debris flying into mud dams at the base of the flume. They were imitating a common and deadly scenario, where a mudslide temporarily dams a canyon, water builds up behind it, and then homes below are destroyed when the whole mess breaks open in a terrifying flood. After each experiment, Iverson feeds the data he’s gathered into predictive models, or computer programs that forecast disasters based on current conditions. Already, he said, he and his colleagues had learned more about flood warning signs after mudslides.

Research at the flume has led to an extremely sophisticated warning system on Mount Rainier in Washington. Several communities on the mountain suffer from periodic landslides due to water runoff, but Iverson and his colleagues were able to plot where these slides were most likely to start. They set up a warning system, a network of sensors that get tripped when a landslide’s characteristic ground vibration begins. When that happens, an alarm system is immediately set off and residents below get 30 to 45 minutes’ warning so that they can escape an event that often ends in death. Engineers at the flume also tested specialized wire nets that now lie like spiderwebs across the hillsides and cliffs above many highways in California, preventing small landslides from spilling onto cars or blocking the road.

Still, Iverson said, he feels like people in the United States don’t think enough about natural disasters when building cities and towns. “Some places really do make use of our predictions for guiding future development,” he replied. “But frankly, in the United States, with our history of zoning laws and development, it doesn’t get taken into great account.” He said that the big problem is that a lot of risky areas, such as the flood-prone Los Angeles canyons, were built up before anyone knew about the danger of mud slides. “You don’t always get to change much, so you do what you can.”

Ideally, Iverson said, he and his team would have enough resources to get detailed topographical maps of any part of Earth so that they could run landslide models of them and determine the safest places for people to build. “We could create probabilistic models for any area that we had data for, showing a range of possible events, from very likely and not so bad, to unlikely and very bad. Showing this information on maps would be very useful for planning purposes.” With the right amount of data, Iverson believes, he could give any planner a fairly realistic prediction about whether future cities might be in danger of getting buried in mud slides the next time a storm hits.

By destroying buildings and causing mud slides, Takhirov and Iverson are able to study disaster as scientifically as possible. What they’ve learned has already affected how cities are built, and how people evacuate flood zones. As we move into the future, however, we want cities that can do more than collapse without killing us. We want cities (and city emergency services) that can change instantly in response to imminent danger. Such cities, though they sound like science fiction, are already in the process of being designed.

Smart Cities and Disaster Prediction

City planners looking to the future often talk wistfully about data acquisition. With enough data about how natural disasters have unfolded in the past, prediction becomes much easier—especially when computers are involved, juggling thousands of data points every nanosecond to create a likely model of the future. That’s why IBM recently launched its Smarter Cities program, which is essentially a suite of software and services that the company sells to cities whose governments want to predict everything from traffic and crime patterns to the best exit strategy in a flood. The goal is to create cities whose traffic, food systems, energy grids, water management, and even health care are managed in a “smart” way, based on real-time data that reveals what’s needed where. This “big data” can come from almost any networked gadgets, including sensors, mobile phones, and GPS devices.

George Thomas, a former structural engineer, heads up the company’s Smarter Cities sales efforts, and has helped implement the program in several urban areas around the world. One of their first projects was to reduce traffic in Stockholm. First, IBM installed cameras over heavily trafficked roads near downtown to gather data. Once they had enough information, they were able to predict peak traffic hours every day. To reduce traffic, the city installed a ring of sensors around the city center that identify the license plates of every car passing through. If cars pass through during a period of high traffic congestion, drivers will automatically be charged a “congestion tax” at the end of the month. Almost immediately, the city found that more people took public transportation, carbon emissions went down, and city revenues went up. Most important, the traffic snarls around the Swedish city were gone.

One of the group’s current projects uses data that engineers like Iverson have been gathering about how mud slides and floods behave. Their goal is to give residents of Rio de Janeiro two days’ warning before the notoriously flood-prone region is inundated with water and mud gushing down from the mountains that ring the city. In the past, emergency responders have only had a six-hour window in which to evacuate, but that’s not long enough. With the city set to host the Olympics and soccer’s World Cup, Rio’s mayor decided to work with IBM to create a system that could predict floods as far in advance as possible. They needed what Thomas called a city operating system—a piece of software that could integrate streaming data from sensors on local flood plains and weather monitors. Working with all this data, the city’s operating system could convert many types of information into a predictive model that would change in real time. With the new system in place, people in Rio will have a full 48 hours to leave their homes and get out of the city before disaster strikes.

Of course, even the best-prepared regions are still going to suffer setbacks. Japan was unprepared for the calamity of the March 2011 earthquake and tsunami. Though the damaged Fukushima Daiichi Nuclear Power Station did have flood-protection walls, they weren’t high enough. And switches that would have brought backup power to the plant’s cooling units hadn’t been adequately flood-proofed either. Could a predictive system with enough data have helped disaster workers prepare for the event? Possibly, though in the wake of the disaster, officials discovered that workers had known about problems at Fukushima for years without addressing them. Predictions are only helpful if city builders are willing to act on them.

The question, as always, is how to build based on what we know. Takhirov thinks the solution lies in the building code, which changes as new discoveries are made. But as Iverson explained, it’s not always easy to change cities that have already been built. All we can do in those situations is to make our cities “smarter.” That’s why engineers around the world are gathering all the data they can about disasters that might hit, in order to offer accurate predictions about when they’ll happen, and how to escape. Cities are more than buildings; they are the people who inhabit them. The philosophy of disaster science is that it doesn’t matter if our structures are damaged as long as people survive. Those people will come back to rebuild the city.

As we’ll see in the next chapter, engineers weren’t the first ones to come up with the idea of modeling urban disasters to save lives. It’s a strategy that works with pandemics, too.

THERE ARE SOME disasters so catastrophic, and so rare, that we have very little data on them. Call them extreme radiation events. As we learned in chapter two, such an event may have caused the second-worst mass extinction on Earth 450 million years ago. Some scientists speculate that a gamma-ray burst coming from a nearby hypernova may have abruptly ended the Ordovician period, frying the ozone layer off our atmosphere and exposing the Earth’s newly diversified multicellular creatures to high doses of radiation. Creatures deep in the sea would have been protected by the radiation-absorbing water, but all the plants and light-loving swimmers near the surface would have been cooked instantly. Those not boiled to death would have been eaten away by radiation fairly quickly as the sun’s ultraviolet rays beamed down on the unshielded planet. A gamma-ray burst like that could hit the planet at pretty much any time, with very little warning. We would likely be able to see the hypernova with our naked eyes, and would have a few short hours before its stream of radioactive particles showered down on the Earth.

Such gamma-ray bursts are a very real threat, but they’re extremely unusual. Even less likely than a hypernova is the probability that its gamma-ray burst would be aimed directly at us. A far more likely cause of sudden radiation bombardment on Earth is human warfare. Even a limited nuclear war could pour ionizing radiation down on the planet in the form of nuclear fallout, causing radiation sickness in the short term and triggering cancers that could kill in the long term.

For people living in cities, it won’t matter if the radiation comes from space or nuclear bombs. To survive, we’ll need to go underground, into subterranean cities whose walls are made of thick layers of rock that can block radiation. We’ve known this for a long time. One of the greatest underground cities of the modern world, the NORAD (North American Aerospace Defense Command) complex beneath Colorado’s Cheyenne Mountain, was designed during the Cold War to protect up to 5,000 residents from atomic blasts and the subsequent fallout. But this isn’t the only underground city humans have built to protect themselves during war. Nearly two millennia ago in what is today central Turkey, Jews and Christians fleeing Rome built villages on top of vast underground cities that could protect thousands of people from Roman raiders—and later, from Muslims during the Crusades.

We’ve been surviving underground for a long time. And city planners today are building more and more underground structures. You may not think you have a chance of surviving during a radiation emergency, but you’re closer to an underground city than you think.

Underground Life

The mounded hills and deep, curving valleys of Göreme, Turkey, are famous for their beauty, and for thousands of undeniably phallic rock columns known as “fairy chimneys.” Though these structures elicit everything from giggles to New Agey declarations about “lingam power” from tourists, what’s most interesting about them isn’t their peculiarly erect shapes. Wind and water have worn them down in this way because the fairy chimneys, like the valleys and cliffs they emerged from, are made of tuff, a pale, crumbly rock composed of highly compressed volcanic ash. Early settlers in Göreme and many neighboring towns in Turkey’s Cappadocia region discovered that tuff was incredibly frangible, and easy to dig out and remold. Small groups of Judeo-Christian mystics driven out of Rome in the second century CE came to central Turkey to hide, and dug spartan monk’s cells into the tuff.

Over the next several hundred years, these tiny settlements of hermits and outcasts grew. Villagers carved out homes, churches, and vast food-storage pantries, eventually creating a breathtaking architectural style in which gorgeous classical columns and arched church doors appear to emerge from solid rock. Local aristocrats funded incredible subterranean art projects, deep cave churches whose high ceilings are painted with gorgeous biblical scenes that could only be seen in torchlight. Many of the most awe-inspiring examples are still preserved in Göreme’s Open Air Museum, a cluster of churches and monasteries carved into the creamy tuff above a valley full of patchwork farms. From a distance, the ornate, sculpted complex looks like an otherworldly city from a Lord of the Rings movie. During the Byzantine era, however, the need for these cave and tunnel cities was all too real.

Cappadocians built dozens of underground cities in the era between the fifth and tenth centuries. Historians have conflicting theories about why, but one major reason would no doubt have been raids from neighboring groups and from Muslims during the Crusades. These underground cities don’t just shield inhabitants from the elements—their entrances are hard to reach, or hidden. They are designed to be invisible.

To imagine how future humans might survive a radiation disaster underground, we need only pay a visit to subterranean Cappadocia. On a drizzly day spent near Göreme, I ducked out of the summer rain to visit Derinkuyu, the most extensive of the excavated underground cities in the region. Now open for tourists, the city’s maze of tunnels, living quarters, and community areas extends five levels and 55 meters underground. Cool and sandy, its often cramped corridors are well ventilated by several air shafts. My tour group and I squeezed down a long stairway, then entered a large room that was once a stable. It could easily have housed a dozen goats, sheep, or cows, chomping contentedly from mangers carved right into the walls. Our guide pointed out that villagers typically entered Derinkuyu via secret tunnels from their aboveground homes. These entrance tunnels were small enough in many places that I was forced to bend quite far down as I walked, and I’m a fairly short person. The city’s builders engineered these areas to discourage anyone trying to enter with bulky weapons or armor. Punctuating many of the stairways were deep crevices that held enormous rock discs designed to roll out and block the corridor from invaders.

Living quarters were honeycombs of interconnected rooms and bed nooks hollowed out of the tuff walls. Though the place looked barren when I saw it, a thousand years ago it would have been very different. People built wooden doors into the round doorways, covering the floors in thick carpets and the walls in draperies. Families from the city above had their own quarters below, full of furniture, favorite pottery, food, and wine. In the living areas of the city, ceilings were high and rooms were cozy rather than cramped. The underground dwellers even had a sanitation solution for long-term sojourns. Waste was packed into clay containers, sealed up, and buried in deep pits below the city’s lowest level. Large public rooms for cooking and eating, as well as wine-making and worship, would have been places where villagers could gather to make decisions about how long to remain underground and hide from danger.

This ancient city, carved out over centuries, was constantly changing and growing. A deep passage connected Derinkuyu with another underground city several kilometers away. The peoples who made these passages their refuges were employing the same survival mechanisms used by Jews over the past 2,000 years—they had scattered from distant communities in both the west and the east, and adapted themselves to the remote landscapes of central Turkey to protect themselves from persecution and ethnic cleansing. Not only did these communities survive for centuries, but they also created an entirely new way of life—one that many people in the area still enjoy today. Traditional villages in Cappadocia are full of homes built into the tuff of fairy chimneys, with narrow stairways spiraling around the rocks’ girth, leading to sturdy wooden doorways in their cone-shaped tops. Some homes are hewn from the cliffs, where they share space with countless pigeon roosts that locals tend for the fertilizer. Tourists are invited to spend the night in refurbished cave homes, as bed-and-breakfasts take over abandoned dwellings. I spent several days in one such hotel, my bed stashed deep inside a cave that had been modified to have large picture windows overlooking the city of Göreme. With the exception of the windows, my bedroom could have been torn from a future world where humans had to relocate underground for protection.

But without those windows, the place would have been much more dismal. And that’s why urban planners creating modern underground cities worry as much about the psychological effects of living underground as they do about the structural integrity of underground spaces.

The Trouble with Tunnels

If we’re going to survive a nuclear war, a meteor strike, or a radiation event, there is no doubt that we’ll have to live underground for months, or even years, as the planet recovers. In the unlikely event that a gamma-ray burst burns off the ozone layer, it could be centuries before life could thrive on the surface again—whenever we stepped outside our underground homes, we’d need to wear protective covering to shield us from the sun’s ultraviolet radiation. The good news is that three feet of packed dirt over your head can significantly reduce the intensity of radiation, and a layer of concrete can provide more safety still. We have the engineering ability to create radiation-shielded cities by going underground. The question is how we would live there.

In the event of a radiation emergency, people might find themselves having to create cities in already-existing underground spaces like subway tunnels, mines, sewer systems, and service tunnels. Already-existing underground cities like Montréal’s “RÉSO,” a 20-mile system of tunnels that connect shopping centers, metro stations, schools, apartments, and more, are basically larger and more complicated versions of mining shafts. To make the long, dark corridors more livable, developers build structures inside the bare rock walls, covering up the stone surfaces.

Making these spaces inviting is crucial to our survival. John Zacharias, a city-planning professor at Montréal’s Concordia University, has studied several underground cities, especially in Japan and China, and told me that the biggest challenge is psychological. Studies on people who work all day in underground space without any access to the outside show rising stress levels. “It’s not dramatic, but is measurable,” he said. “Going down very deep is also something people don’t like.” The new Oedo subway line in Tokyo is 55 meters below the surface, and Zacharias said people tend to avoid it in favor of an overcrowded line it was supposed to relieve. In Finland and Sweden, where underground buildings are common, studies have shown that people are disturbed by the process of descending into the Earth, and that they complain of the monotony in subterranean buildings. The solution, argue civil engineers John Carmody and Raymond Sterling in Underground Space Design, their underground-engineer omnibus, is to make sure underground spaces are “stimulating, varied environments” that give the impression of spaciousness and daylight.

Many underground cities, like RÉSO, use skylights to bring in daylight, but our future troglodytes won’t have that option because they will need radiation shielding. So they’ll have to arrange underground areas to be different sizes and shapes, with architectural features that make the space interesting to inhabit. Even the residents at Derinkuyu knew this, and their interior spaces were all uniquely arranged, with a wide variety of floor plans. Carmody and Sterling also caution that one of the main complaints people have underground is that they become disoriented without windows, so a good underground city would need a simple layout or clear signs that help inhabitants find their way. Because people get anxious about going deep underground, transitions between levels should be gradual. Ideally, different areas of the city would have dramatically different designs to give the feeling of neighborhoods and landmarks that we use aboveground to figure out where we are. Privacy will also be a premium in spaces like these, where people have a tendency to feel trapped. As we turn our tunnels into our homes, we’ll want to remember to create places to be alone, as well as vast, high-ceilinged rooms that will make us feel as if we’re outdoors even if we aren’t.

If we are turning mines into cities, or excavating a brand-new subterranean metropolis, there are also a few basic engineering issues we should keep in mind. Agust Gudmundsson, a geology professor at Royal Holloway, University of London, studies underground structures, and he explained that earthquakes will be a threat to life belowground. “Fractures that form or are reactivated during an earthquake may lead to water flowing into parts of the underground city,” he said. Water leakage is one of the main causes of destruction in these developments, and leaks recently led to partial collapse of some tunnels in RÉSO. When we build underground, Gudmundsson cautioned, we have to be vigilant about whether we’re building in regions with faults or cracks—especially if the city will be near a body of water. Just building the city could cause tremors that allow water to come seeping through cracks, causing damage or collapse over time. At the NORAD facility in Colorado, the water-leakage problem was so severe that people walked under umbrellas through the long rock tunnel that winds deep into the mountain and to the massively reinforced city gates.

Nowhere to Go but Down

“The construction of major transit projects such as metros and road tunnels is just a prelude for the true nature of underground development,” argue Dmitris Kaliampakos and Andreas Barnardos, two engineers who specialize in underground development at the National Technical University of Athens. In 2008, the two helped organize an international conference to deal with questions about building underground. Over the past few decades, many cities have witnessed the proliferation of underground building projects, ranging from individual homes expanding underground to RÉSO-like structures such as the one Amsterdam considered building beneath its canals in the late 2000s. “The main driving force behind the process is the continuously growing urban areas,” write Kaliampakos and Barnardos. Building underground saves energy, they point out, because subsurface temperatures stay comfortable year-round; in addition, it allows cities to expand without destroying historic places or producing suburban sprawl. The problem is that most cities don’t have a lot of regulations and codes in place to help developers make these underground spaces. It’s hard for real-estate agents to value underground spaces that don’t exist, and most laws don’t make it clear who owns the land below our feet. These factors, along with the cost of building down, make developers shy about breaking ground.

Still, the laws are catching up with urban needs. And geologists like Gudmundsson are working with engineers to provide accurate maps of the kinds of rocks and fissures that lurk beneath us, so that we can plan the right spots to tunnel below. As John Zacharias said, “We are going to have a lot more space underground in future, especially as cities build new transportation systems underground.” He predicted that the movements below will also be related to concerns about energy. “We will need places to store water, especially as cities get round to recycling water,” he asserted. “Power plants will go underground. Theaters and libraries are already there. The future city is three-dimensional, and all big cities will be looking to see how they can better use the underground resource.”

As more cities send vital roots underground, we create a world that is inadvertently preparing itself for a radiation emergency. The more we make the subsurface livable, the more likely it is that humans will survive to see the next several millennia.

In this description of underground cities, we’ve considered city designs that would make us comfortable living underground, and we’ve learned that our worst enemy underground will be seeping water. But we’ve danced around the real issue we’ll confront in our radiation-proof cities: food. As the atmospheric scientist Alan Robock of Rutgers University points out in one of his many papers on nuclear winter, the biggest issue we’ll face may not be radiation at all. It will be starvation in the wake of extensive burning:

Famine will also be a problem if one of our planet’s many megavolcanoes goes off. Ash and soot from such an enormous eruption would be blasted into the stratosphere, cutting the planet off from life-giving sunlight. The atmosphere would likely be full of sulfides and dust as well, both of which we’d want to avoid. So we might be looking at generations who live much of their lives underground. Our underground cities will have to be farms as well as shelters. In the next chapter, we’ll explore in greater detail how such farms might work.

Just like underground cities, farm cities are being built already, for many of the same reasons. Farm cities, like the green cities the urban geographer Richard Walker described in his book on San Francisco, are far more energy efficient and environmentally sustainable than the industrial cities most of us inhabit today. They are also less likely to suffer famine. In the next chapter, we’ll speculate about what cities might look like in a century or two. It’s possible they’ll be nearly indistinguishable from the natural surface of the planet.

WE’VE EXPLORED HOW cities are not static objects to be feared or admired, but are instead a living process that residents are changing all the time. Given how much bigger and more common cities are likely to become in the next hundred years, we’ll need to change them even further. Using predictive models from the fields of engineering and public health, our future city designers will plan safer, healthier cities that could allow us to survive natural disasters, pandemics, and even a radiation calamity that drives us underground. But there is a yet more radical way we’ll transform our cities. Over the next two centuries, we’ll probably convert urban spaces into biological organisms. By doing this, we make ourselves ready to prevent two of the biggest threats to human existence: starvation and environmental destruction.

Eventually this biological transformation might result in cities unlike any that have existed before. But for now, the best way to understand how such a shift would begin is by paying a visit to a city park or garden. These are places that we’ve built in the middle of cities to closely resemble the natural world. Usually they are just as engineered and artificial as the buildings surrounding them, but they do a lot of things that buildings typically can’t do, such as sequester carbon, absorb runoff storm water, and provide a cool, shady environment without drawing any energy from the grid. Many city parks today are reclamations of previously blighted areas. In Vancouver, Canada, for example, residents of the Fairview neighborhood converted a stretch of abandoned railroad tracks into dozens of garden plots where locals grow vegetables, flowers, and grains around the still-visible iron rails. And in New York City, a group of enthusiasts lobbied the city to let them convert a historic elevated-train structure into a park, which is now called (appropriately enough) the High Line. This once abandoned viaduct now features trees and grasses that seem to sprout from its concrete columns. People in these cities and many others throughout the world are slowly blanketing their barren causeways in habitats where plants and animals can thrive.

If we want the populations of our cities to survive, however, we’re going to have to do a lot more than plant flowers in lower Manhattan. We’ll need to transform urban areas into regions that can, as much as possible, feed themselves. That means prairie cities can’t rely on distant countries for bananas, nor can people living in desert outposts expect to get grain from fertile basins hundreds of kilometers away. More pressingly, we need to build cities that draw energy from their local ecosystems. By growing biofuels, and using sunlight for power, we make it less likely that humanity’s home planet will one day no longer sustain our need for energy. The biological city could provide us with food and energy security for millennia to come.

Food on the Streets

When I visited Cuba in the early 2000s, the best places to buy fresh food in Havana were street markets where urban farmers sold whatever they’d cultivated on roofs or in window boxes, sidewalk gardens, and yards. I wandered around in one of these markets, located in a large, airy warehouse where a couple of dozen people had set out their goods in baskets and on blankets. One woman was selling four eggs, a few eggplants, and a cellophane bag of spices. Another sat back on her heels behind a blanket heaped with greens. Street markets occupied a precarious legal position under communism because they encouraged private enterprise. But instead of cracking down, the Cuban government was paying agricultural engineers to study the most productive methods of urban farming. The need to prevent starvation overrode ideological concerns.

Though that ad-hoc urban farmer’s market in Havana felt like a medieval oasis in the middle of a bustling, cosmopolitan city, it was actually a good demonstration of how people might grow and buy their food in the cities of tomorrow. They’ll do it by slowly converting cities into farms. At the time I was in Cuba, Raquel Pinderhughes, an urban planning professor at San Francisco State, wrote that there were over 8,000 farms in Havana, covering about 30 percent of the region’s available land. If you rode into the countryside on a bus that picked you up on Havana’s busy Malecón, a promenade along the seawall, you’d find that the high-density city quickly shaded into suburban residential areas peppered with farmland. Land planners sometimes call this system periurban agriculture. It transforms suburban consumer sprawl into a rich source of food production.

In the hot, dry valleys of Pomona, California, a nonprofit group called Uncommon Good has helped set up an urban farm where unemployed immigrants with farming experience grow organic food to sell in local markets. This Pomona farm, like many others, uses the “small-plot intensive farming” (SPIN) model, designed by urban farmers in Canada to maximize crop yields in areas of less than an acre. The idea behind SPIN is both agricultural and economic. Farmers vary their crops and use sustainable fertilizers to keep their small plots of soil fecund, and they sell by direct marketing in their local areas. This maximizes food production and minimizes the resources that the farmers need to transport that food to buyers. It’s easy to imagine many cities transformed by a SPIN model over the next 50 years, where people grow their own food to eat and sell to neighbors—who in turn sell different food, so that local diets can remain varied.

But will cities transform farming as much as urban farmers hope their methods will transform cities? In his book The Vertical Farm: Feeding the World in the 21st Century, Columbia University environmental-health professor Dickson Despommier argues that cities of the future might feed themselves by creating farms inside enormous, glass-walled skyscrapers where every floor is a solar-powered greenhouse. All water in these skyscraper farms would be recycled, and the structures themselves would be designed to be carbon neutral. While critics question whether it would be possible to heat, power, light, and tend skyscraper farms without wasting a lot of energy, Despommier’s thought experiment is a good one. We are going to need ways to produce enormous amounts of food in cities, often indoors, and trying to figure out how we’d do that in a skyscraper—or an underground cavern, for that matter—is a step in the right direction.

Our future buildings may be sprouting gardens on the outside, too. A popular way to transform cities in Germany is by building green roofs, which are basically special systems designed to convert rooftops into gardens. This isn’t just a matter of heaping some dirt up and throwing seeds on it. Green roofs are a complex system of layers designed to protect the roof, absorb water, and hold soil in place. Though they are unlikely to be useful for farming, some studies have shown that green roofs help cut energy costs by keeping buildings cooler in the summer months. They also reduce storm-water runoff, which is a huge issue in cities. Because most cities are covered in nonporous, nonabsorbent surfaces, all the grime, toxins, and trash in the city are washed out by rainwater during storms—and carried into nearby waterways, farms, and oceans. Having a roof that can absorb rainwater does a tremendous amount of good for the local environment and cuts costs related to water purification and treatment.

Bringing natural environments into cities isn’t just about feeding ourselves. It’s also about figuring out how to manage our energy consumption using tricks borrowed from nature. Growing shade plants on our roofs can help cut energy costs in summer, just as designing photosynthetic antennae like the ones mentioned in chapter 11 can help us power computers without burning coal. Natural ecosystems conserve energy remarkably well. As we learn to imitate that, our cities might become highly advanced technological entities that look strangely like the postapocalyptic jungle version of New York City in The World Without Us.

Managing the Land

MIT’s environmental-policy professor Judith Layzer offered me a vivid picture of what life might be like in such a city. She believes that, ideally, most future human communities would be based in cities, leaving enormous stretches of land free for farms and wildlife. “We need to re-regionalize,” she told me. “A global economy doesn’t make sense environmentally. So your ecosystem would become your bioregion.” She described a world where communities would be organized around bioregions like the dense forests and rocky coasts of the mid-Atlantic states or the prairie grasslands of North America’s Great Basin. “Most of your food should come from your region,” she said, and farm labor would be done by people rather than machines. But, she asserted, “nobody would be working as hard as they are now” because life would have a much slower pace. “You’d have goats mowing lawns,” she said, her face quirking into a grin. “It would be less efficient in the contemporary sense. Long-distance travel would be more of a hassle. You’d bike everywhere.” In her ideal city, where food was local and energy carbon neutral, “you’d do everything with natural systems.” And the population of a city would never rise above a few million.

This kind of regionalism might be good for our ecosystems, but it probably couldn’t be as “natural” as Layzer imagines. Obviously, if people are depending on their bioregion for food, they’ll be more vulnerable to the vicissitudes of climate and seasonal drought. We’ll need cutting-edge technology to help these bioregional cities weather periods when the local ecosystem can’t support the population.

One possible way we’ll do this is by looking to outer space. At UC Santa Barbara, an international group of climate scientists, geographers, and geologists use satellite data to predict where drought will strike next. They call themselves the Climate Hazards Group, and their success at predicting drought is almost uncanny. Currently, they focus most of their efforts on Africa. Amy McNally, a geography researcher with the group, said she and her colleagues helped predict the summer 2011 drought in Somalia by correlating data drawn from satellite images of rainfall in the region with rain gauges on the ground. “They predicted the drought and the resulting famine a year in advance,” she said. Unfortunately, “even with that much forewarning, response didn’t make it in time for it to not get to a famine-level crisis.” But the group had gained more evidence about what signs indicated droughts to come.

One of the key indicators comes from satellite observations of greenery on the ground. Just as green roofs keep buildings cooler, a green ground cover keeps the soil cooler, wetter, and more likely to yield a good crop. When plants die back too much, drought may be on its way in the next season. McNally said the satellite she uses measures the wavelengths of light reflected back from the West African region she studies. Plants reflect green light back into space, where the satellites measure percentages of green light versus other wavelengths. As a result, McNally can get an extremely precise picture of how much green is required on the ground to guarantee a good growing season. The big issue in Africa is that most regions don’t use extensive irrigation, so farmers are dependent on rainfall for a successful crop. A dry season can mean death. But it doesn’t have to.

Knowing we’ve got an impending drought might mean shoring up water supplies for irrigation that could keep a valuable plant cover protecting the soil. As our cities become more closely tied to their bioregions, science teams like the Climate Hazards Group could become crucial to urban planning. With the technology and data we have now, McNally said, “we can make predictions like ‘In the next twenty years, you’ll have five droughts, which is two more than usual.’” This kind of information could prove invaluable to farmers planning their water usage, or governments trying to set up trade arrangements with areas that won’t be affected by the drought. As we gather more data on how droughts happen, we may be able to make more accurate predictions about when famine is likely to strike—and stop it before it starts.

Satellite imagery and technology are not a panacea for food-security problems. In fact, as we discussed earlier, famine is usually caused by political and social upheaval. Fixing that will require more than good science. You could say the same thing about our energy problems. But it’s possible that our political priorities will change along with our changing urban environments.

The Biological City

As we move further into the future, our cities won’t just be swaddled in gardens and farms. They might also become biological entities, walls hung with curtains of algae that glow at night while sequestering carbon, and floors made from tweaked cellular material that strengthens like bones as we walk on it. New York architect David Benjamin is part of a new generation of urban designers who collaborate with biologists to create building materials of the future. I met him in Studio-X, a branch of Columbia University’s school of architecture located in a bare-bones whitewashed work space south of Greenwich Village. Students focused on monitors full of three-dimensional renderings of buildings, or sketched at drafting tables between concrete columns. It looked like the kind of place that could, in 50 years, be sprouting a layer of grass from its walls—or something much stranger than that.

Benjamin described the shift to biological cities using quick, precise gestures that reminded me of someone penciling lines on a blueprint. “It might look the way it looks now,” he said. “The city could be made with bioplastics instead of petroleum plastics, but it would look very similar. A machine for making genetically modified organisms (GMOs) would exist in factories the way they do today for making medicine and biofuels.” So the plastic fittings around windows would be manufactured from modified bacteria rather than fossil fuels, but as a city dweller you’d notice little difference. Benjamin and a group of other architects and biologists have worked with Autodesk, the company that makes the popular AutoCAD software many architects use to design buildings, to create a mock-up of AutoCAD for biological designs, called BioCAD. Pulling out his laptop, Benjamin showed me a demonstration of the biological-design-software interface. The designer can choose between biological materials with different properties, like flexibility or strength. Having chosen those, the designer directs the program to create structures that look like marble cake, a multicolored swirl of substances combined into a single structure that gives in the right places and holds steady in others.

Over time, these living cities would start to look different. They’d be transformed by synthetic biology, a young field of engineering that crafts building materials from DNA and cells rather than more traditional biological materials like trees. Benjamin described a recently created synthetic-biology product called BacillaFilla, designed by a group of college students in England. The students engineered a common strain of bacteria to extrude a combination of glue and calcium when put into contact with concrete. They applied the bacterial goo to cracks in concrete, and over time it filled the cracks completely and then died, leaving behind a strong, fibrous substance that has the same strength as concrete. The students described BacillaFilla as the first step toward “self-healing concrete,” and their efforts are just one among many designed to create biological substances that could heal ship hulls, metal girders, and more.

Extrapolating from this development in synthetic biology, Benjamin mused, “Maybe you could program a seed to grow into a house. Or maybe cities would be so in tune with ecosystems that they would grow over time, and then decay over time, too.” Synthetic biology might also help solve one of the biggest problems with new buildings, which is water leakage. Architects could design a building that is semi-permeable, with membranes that allow the circulation of air and water at various times. It’s easy to imagine a future architect fashioning just such a thing with BioCAD, with patches of permeable materials built right into the fabric of the walls. The water could be purified and used, and the air would become part of a natural cooling or heating system. This building might also use computer networks to monitor its community of local buildings to figure out when to gather solar energy and send it to the grid to share, and when to lower louvers to keep residents cool. “I sometimes imagine urban landscapes that are integrated into their ecosystems with a combination of vegetation and constructed materials,” Benjamin said. “They look almost like ruins in the jungle but they’re actually fully functional, occupied cities.”

Benjamin’s visions of the future end where his fellow synthetic-biology designer Rachel Armstrong’s begin. Armstrong, who is based in London, is an outspoken advocate for what she calls “the living city,” or urban structures that she told me we’d create in the same way we cook or garden. We met in a café in the heart of London, overlooking the busy Tottenham Court Road, and almost immediately Armstrong was imagining how she’d rebuild the city around us. “We’d have biofuel-generated façades, or technology based on algae,” she said, pointing at the windows. “You’d have surfaces creeping down buildings like icing. Strange, colored panels would glow through windows at night, and you’d have bioluminescent streetlights. Bridges will light up when we step on them.” She paused, but continued staring outside, deep in thought. “We’d keep the bones of buildings steel and concrete, but rewrap those spaces with increasingly more biological façades. Some will be porous and attract water; others will process human waste. Mold won’t be something you clean off a surface but will be something you garden.”

Armstrong is fascinated by bacteria and mold, which she and other synthetic-biology designers view as the building blocks of future cities. “We are full of microbes,” she asserted firmly. “Maybe instead of using environmental poisons to create healthier environments inside, we should be using probiotics.” Glowing bacteria could live in our ceilings, lighting up as the sun goes down. Other bacteria might purify the air, scrubbing out carbon. Every future urban home would be equipped with algae bioreactors for both fuel and food.

Her vision isn’t just science fiction. Recently, Armstrong worked with a group of biologists and designers who hope to use experimental proto-cells—basically, a few chemicals wrapped in a membrane—in a project that could prevent Venice from sinking into the water. Proto-cells are semi-biological, and can be designed to carry out very simple chemical processes. In Venice, engineers would release proto-cells into the water. Designed to prefer darkness, the proto-cells would quickly head for the rotting pilings beneath the city’s dwellings. Once attached to the wood, the cells would slowly undergo a chemical transformation in which their flexible membranes transformed into calcium shells. These calcium shells would form the core of a new, artificial reef. As wildlife discovered the calcium deposits, a natural reef would form. Over time, the city’s shaky foundations would become a stable reef ecosystem. Already, Armstrong and her group have had some success creating small-scale versions of the proto-cell reef in the lab, and they’re moving on to experiments in controlled natural areas.

If our cities do evolve to be more like biological organisms and ecosystems, it could change the way communities form within their walls. “We might start to experience the city as something we have to take care of the way we take care of our bodies,” Armstrong suggested. In a biological city, using toxic chemicals in your kitchen might cause your algae lights to die. “We’ll take more care of the city because we feel its injuries more deeply,” Armstrong said. It’s possible that this would generate a sense of collective responsibility for our buildings and avenues. Neighbors would tend their buildings together, trading recipes for making fuel the way people today trade recipes for holiday cakes.

Armstrong’s hyper-technological biometropolis shares something in common with Judith Layzer’s vision of small, slow cities devoted to farming. Both of them arise from the belief that city dwellers will become producers rather than consumers. With home bioreactors, Armstrong said, “our spaces will become a place where we can generate wealth.” This idea is central to the SPIN model of urban farming, too. “It’s about decentralizing energy and food production, basically,” Armstrong concluded. Of course, it’s impossible to predict what the consequences would be for people in cities whose buildings were half-alive. Armstrong is willing to admit her ideas are utopian, and that’s the point. “You need something to aim at,” she said with a smile.

As we look further to the future in the next part, we’ll be taking aim at something even more speculative than self-healing cities that look like glowing ruins and sprout food and power from every surface. We’ll see what humanity might become if we manage to survive for another million years. To do this we’re going to need to do more than rebuild our cities. We’ll need to rebuild the entire Earth. And then we’ll start striking out for the territories beyond our planet, lifting ourselves into space and colonizing the solar system. What will humans be like after tens of thousands of years of evolution, especially in space? It’s possible that our progeny will be as unlike us as we are from Australopithecus—and yet they will still be as human as our distant hominin ancestors were.