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Illustration by Joe Kloc
Four-and-a-half years ago, Hurricane Katrina plowed into the coast of Louisiana, pummeling New Orleans for eight hours straight with high-speed winds and storm surges reaching 15 feet. Swollen beyond capacity, Lake Pontchartrain spilled into the northern part of the city, and the federal flood protection system, built to protect NOLA from a repeat of Hurricane Andrew, failed in more than 50 places. One day later, nearly every levee in the metro district had been breached, leaving 80 percent of the city underwater.
In the aftermath, Americans watched in disbelief as thousands of newly homeless poured into the Superdome for shelter and TV cameras captured those left behind clinging to rooftops, wading through the streets, and looting empty storefronts. Scenes of destruction, desperation, and poverty, made only more poignant by the overwhelming evidence of official negligence. New Orleanians themselves, as the New York Times put it, were left “terrified, stunned, gasping, speechless.”
But to some scientists, what happened in New Orleans, while devastating, wasn’t very surprising or unexpected. They see a system that was insufficiently robust to handle the blow it was dealt. They see a highly ordered, complex state—commercial districts and neighborhoods, social networks and infrastructure networks, cycles of water, energy, and food consumption—reduced to a state of chaos and disorder. From this perspective, the problem wasn’t merely an incompetent leadership and not enough FEMA trailers. It was a fundamental question of resilience.
Resilience theory, first introduced by Canadian ecologist C.S. “Buzz” Holling in 1973, begins with two radical premises. The first is that humans and nature are strongly coupled and co-evolving, and should therefore be conceived of as one “social-ecological” system. The second is that the long-held assumption that systems respond to change in a linear, predictable fashion is simply wrong. According to resilience thinking, systems are in constant flux; they are highly unpredictable and self-organizing, with feedbacks across time and space. In the jargon of theorists, they are complex adaptive systems, exhibiting the hallmarks of complexity.
A key feature of complex adaptive systems is that they can settle into a number of different equilibria. A lake, for example, will stabilize in either an oxygen-rich, clear state or algae-dominated, murky one. A financial market can float on a housing bubble or settle into a basin of recession. Historically, we’ve tended to view the transition between such states as gradual. But there is increasing evidence that systems often don’t respond to change that way: The clear lake seems hardly affected by fertilizer runoff until a critical threshold is passed, at which point the water abruptly goes turbid.
Resilience science focuses on these sorts of tipping points. It looks at gradual stresses, such as climate change, as well as chance events—things like storms, fires, even stock market crashes—that can tip a system into another equilibrium state from which it is difficult, if not impossible, to recover. How much shock can a system absorb before it transforms into something fundamentally different? That, in a nutshell, is the essence of resilience.
The concept of resilience upends old ideas about “sustainability”: Instead of embracing stasis, resilience emphasizes volatility, flexibility, and de-centralization. Change, from a resilience perspective, has the potential to create opportunity for development, novelty, and innovation. As Holling himself once put it, there is “no sacred balance” in nature. “That is a very dangerous idea.”
Over the past decade, resilience science has expanded beyond the founding group of ecologists to include economists, political scientists, mathematicians, social scientists, and archaeologists. And they have made remarkable progress in studying how habitats—including coral reefs, lakes, wetlands, forests, and irrigation systems, among others—absorb disturbance while continuing to function.
New Orleans, however, presents an interesting example to resilience scientists. If a lake can shift from clear to murky, could a city shift to a dramatically different stable state too? If biodiversity in ecosystems makes them resilient to disturbance, could diversity in urban systems serve a similar purpose? “Cities aren’t dominated by nature to the same extent as things like lakes and wetlands and coral reefs,” says Australian ecologist Brian Walker, “But we wondered, could we look at them in the same way?”
In 2008, a historic milestone was crossed, with more than half of the world’s population now living in cities. The UN estimates that by 2030, the planet’s current 2.9 billion urban residents will rise to a staggering 5 billion. By 2050, humanity may well be 80 percent urban.
Urban centers have always been hubs of innovation, creativity, and wealth, but they are also hubs of crime, disease, and environmental pollution. Cities can be models of resource efficiency—the average Manhattanite uses only 29 percent of the energy an average American uses in a year—but they also concentrate the need for huge amounts of power, water, food, and other resources. In the developing world, cities are changing faster than scientists can understand the diverse factors driving those changes, and to complicate matters further, many of those forces operate in contradictory directions and at differing scales.
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