Does climate change threaten international peace and security? The British government thinks it does. As this month’s head of the United Nations Security Council, Britain convened a debate on the matter last Tuesday. One in four United Nations member countries joined the discussion — a record for this kind of thematic debate.

Countries rich and poor, large and small, and from all continents — Bangladesh, Ghana, Japan, Mexico, much of Europe and, most poignantly, a large number of small island states endangered by rising seas — recognized the security implications of climate change. Some other developing countries — Brazil, Cuba and India and most of the biggest producers of fossil fuels and carbon dioxide, including China, Qatar and Russia — either questioned the very idea of such a link or argued that the Security Council is not the right place to talk about it.

But these skeptics are wrong. Evidence is fast accumulating that, within our children’s lifetimes, severe droughts, storms and heat waves caused by climate change could rip apart societies from one side of the planet to the other. Climate stress may well represent a challenge to international security just as dangerous — and more intractable — than the arms race between the United States and the Soviet Union during the cold war or the proliferation of nuclear weapons among rogue states today.

Congress and senior military leaders are taking heed: Legislation under consideration in both the Senate and the House calls for the director of national intelligence to report on the geopolitical implications of climate change. And last week a panel of 11 retired generals and admirals warned that climate change is already a “threat multiplier” in the world’s fragile regions, “exacerbating conditions that lead to failed states — the breeding grounds for extremism and terrorism.”

Addressing the question of scientific uncertainty about climate change, Gen. Gordon R. Sullivan, a former Army chief of staff who is now retired, said: “Speaking as a soldier, we never have 100 percent certainty. If you wait until you have 100 percent certainty, something bad is going to happen on the battlefield.”

In the future, that battlefield is likely to be complex and hazardous. Climate change will help produce the kind of military challenges that are difficult for today’s conventional forces to handle: insurgencies, genocide, guerrilla attacks, gang warfare and global terrorism.

In the 1990s, a research team I led at the University of Toronto examined links between various forms of environmental stress in poor countries — cropland degradation, deforestation and scarcity of fresh water, for example — and violent conflict. In places as diverse as Haiti, Pakistan, the Philippines and South Africa, we found that severe environmental stress multiplied the pain caused by such problems as ethnic strife and poverty.

Rural residents who depend on local natural resources for their livelihood become poorer, while powerful elites take control of — and extract exorbitant profits from — increasingly valuable land, forests and water. As these resources in the countryside dwindle, people sometimes join local rebellions against landowners and government officials. In mountainous areas of the Philippines, for instance, deforestation, soil erosion and depletion of soil nutrients have increased poverty and helped drive peasants into the arms of the Communist New People’s Army insurgency.

Other times, people migrate in large numbers to regions where resources seem more plentiful, only to fight with the people already there. Or they migrate to urban slums, where unemployed young men can be primed to join criminal gangs or radical political groups.

Climate change will have similar effects, if nations fail to aggressively limit carbon dioxide emissions and develop technologies and institutions that allow people to cope with a warmer planet.

The recent report of Working Group II of the United Nations Intergovernmental Panel on Climate Change identifies several ways warming will hurt poor people in the third world and hinder economic development there more generally. Large swaths of land in subtropical latitudes — zones inhabited by billions of people — will experience more drought, more damage from storms, higher mortality from heat waves, worse outbreaks of agricultural pests and an increased burden of infectious disease.

The potential impact on food output is a particular concern: in semiarid regions where water is already scarce and cropland overused, climate change could devastate agriculture. (There is evidence that warming’s effect on crops and pastureland is a cause of the Darfur crisis.) Many cereal crops in tropical zones are already near their limits of heat tolerance, and temperatures even a couple of degrees higher could lead to much lower yields.

By weakening rural economies, increasing unemployment and disrupting livelihoods, global warming will increase the frustrations and anger of hundreds of millions of people in vulnerable countries. Especially in Africa, but also in some parts of Asia and Latin America, climate change will undermine already frail governments — and make challenges from violent groups more likely — by reducing revenues, overwhelming bureaucracies and revealing how incapable these governments are of helping their citizens.

We’ve learned in recent years that such failure can have consequences around the world and that great powers can’t always isolate themselves from these consequences. It’s time to put climate change on the world’s security agenda.

Thomas Homer-Dixon, director of the Trudeau Center for Peace and Conflict Studies at the University of Toronto, is the author of “The Upside of Down: Catastrophe, Creativity and the Renewal of Civilization.”

Five Years After the Reverberations of 9/11: Considering the causes of terror is neither softheaded idealism nor the appeasement of evil, says conflict analyst Thomas Homer-Dixon

Since 9/11, millions of words have poured from our popular media into our brains about the nature of al-Qaeda, about divisions and discord within the Islamic world, and even about the ingredients for liquid explosives. This torrent of information has enlightened us about terrorism in some ways, but in others it has left us as befuddled as ever. And nothing has confused us more than the question of whether it’s worthwhile, or even morally justified, to talk about terrorism’s “root” causes.

Are there deep economic, social, political, or psychological causes of terrorism — things such as economic inequality, militant religious fundamentalism, or feelings of alienation and humiliation — and, if so, should we discuss them, analyze them, and then try to address them through our domestic and foreign policies?

To many people — including this paper’s editorial board and several of its columnists — any discussion of root causes is simply an exercise in making excuses for terrorism. It shifts blame from where it should reside — squarely on the heads of the terrorist perpetrators themselves — to other people or impersonal external forces. In particular, the claim that the West’s foreign policy is the root cause of Islamic terrorism amounts to little more than blaming the victim. At its best, consideration of root causes is softheaded idealism. At its worst, it’s appeasement of evil.

In the passion that marks the aftermath of a terrorist attack, such arguments are understandable. But that doesn’t make them sensible. In fact, they’re downright dangerous. They could deprive us of knowledge and insights that might be decisive in our long-term struggle with terrorism. None other than Hans Morgenthau, one of the architects of the conservative realist school of international relations scholarship, recognized the vital importance of a “respectful understanding” of one’s adversaries. “The political actor,” he wrote more than 50 years ago, “must put himself into the other man’s shoes, look at the world and judge it as he does.”

To argue against analysis and discussion of root causes is to argue for blind ignorance, and in our new world — where small groups of people may soon be able to destroy entire cities with nuclear or biological devices — blind ignorance could be costly indeed.

That being said, the issue of terrorism’s causes is truly a minefield. I’ve followed scholarship and popular commentary on the topic for 20 years, collecting shelves of books and many thick files of clippings and articles. Taken as a whole, this literature covers just about every imaginable cause. Some of it is thoughtful and well-researched, but too much of it, alas, is little more than ideological posturing by commentators on the political right or left. And a surprising amount of it is handicapped by some very basic analytical mistakes.

Take, for instance, the common tendency to conflate moral and causal assessments of terrorism. Conservative commentators, especially, often say that terrorism’s fundamental cause is nothing more than human wickedness or evilness. To argue anything else, they say, is to justify and legitimize atrocity. Yet, while it’s satisfying and morally appropriate to condemn terrorist attacks as evil, such condemnation doesn’t really tell us much about why they happen. To say that evil happens because people are evil is circular. And the effort to diagnose terrorism’s underlying causes — the roots of the evil, if you will — doesn’t imply moral approval of the terrorism.

When it comes to terrorism, we need to have two kinds of discussion within our democracies. One should be about the moral character of terrorism and its perpetrators — and here it’s entirely appropriate to use words such as “evil.” The other should be about the social and psychological factors that contribute to terrorism. The two discussions, both vitally important and inevitably connected, are nevertheless distinct. We can condemn terrorism as a moral abomination at the same time we try to figure out why it happens, just as we do with criminal behaviour in our societies, such as murder and child abuse.

Another common mistake is to say that terrorism is caused by one thing — such as poverty, Islamic radicalism, capitalism, rapid modernization, or cultural insecurity. We all have our favourite cause, and it’s usually something that makes sense within our ideological worldview. Conservatives, for instance, will often emphasize deep-seated cultural factors as the cause — such as a tendency, supposedly intrinsic to Islamic culture, towards radicalism and violence. Those on the left of the political spectrum, on the other hand, will often stress economic factors such as poverty and inequality.

Once we’ve identified our favourite single cause, we frequently set up opposing arguments as straw men. A popular strategy is to find a few cases where the opposing argument doesn’t work and to assert that, therefore, it’s always wrong. For instance, if we believe that the cause of terrorism is Islamic radicalism, while our opponent argues that it’s poverty, we’ll try to discredit our opponent’s argument by pointing to cases — such as 9/11 — where the terrorists were relatively well off. Or we’ll note that the vast majority of poor people aren’t terrorists. Of course, our opponent can do the same kind of thing by pointing to cases where Islamic radicalism isn’t a factor in terrorism, including Tamil suicide attacks in Sri Lanka.

Such mudslinging over the relative merits of single-cause explanations of terrorism is utterly pointless. It gets us nowhere, because complex social events are never caused by one thing. Any particular event — whether a war, economic recession, treaty negotiation, or instance of terrorism — is always the product of the combined influence of an incalculable number of factors. The influence of any one factor will depend on the specific constellation of other factors operating in that case. So sometimes poverty might be an important cause of terrorism, and sometimes not, depending on what else is going on.

Does this mean that every terrorist attack is different? Yes it does. Does it mean that we can’t say anything in general about terrorism’s root causes? No it doesn’t. Careful research can identify common patterns of factors across cases — factors that occur frequently enough that we can say with confidence that they’re significant causes of the general phenomenon we call terrorism.

Since 9/11, scholars have carried out and published an enormous number of studies. They’ve run statistical analyses of reams of data on the characteristics of terrorists and their backgrounds, and they’ve interviewed thousands of terrorists and their friends, acquaintances, and family members.

From this research, a clearer picture of terrorism’s underlying causes is beginning to emerge. This picture suggests that participants in terrorism tend to be men in their twenties or thirties who are ferociously angry because of powerful feelings of humiliation. The humiliation can have many sources, but it’s likely to arise when relatively well-educated young men are deeply frustrated by a lack of political and economic opportunity and when, at the same time, they strongly identify with a group, society, or culture they perceive as oppressed or exploited. Extremist leaders then inflame and manipulate these feelings of humiliation, partly by defining the “enemy” — the group or society that’s responsible for all problems and that should be the target of attack.

So far this research hasn’t had much influence on our public conversation about terrorism in Western societies. Instead, too many commentators seem mainly interested in scoring cheap ideological points. But if we don’t prepare ourselves better to deal with terrorism, especially by understanding and doing what we can about its deep causes, we’ll eventually pay a heavy price. It’s very unlikely we’ll defeat this menace through military force alone.

“If there’s another major attack, people will leave the city in droves.”

Andrew, a colleague of mine in New York City, was sitting in his office in a building not far from Grand Central. It was October 2001, and I’d phoned him from Canada to discuss some business. But our conversation quickly turned to the city’s fevered mood. After the attack on the World Trade Center and a string of anthrax letters, New York’s normally thick-skinned inhabitants were near their tipping point.

Of course, another attack never occurred, so we’ll never know just how close New Yorkers came to the leaving the city en masse. But Andrew clearly thought that the psychological pressure on the city’s people had reached a critical threshold.

I’ve been reflecting on Andrew’s comment since hearing the awful newsflash about the second round of subway bombings in London last Thursday. His comment highlights, I think, the first of three factors that together make modern societies increasingly vulnerable to terrorism: how we define or “frame” these attacks in our minds. The second is the increasing brittleness of the hyper-complex technological and social systems. And the third is the rising technological power of terrorists to hurt us.

We can do a lot about the first factor; we can do quite a bit about the second; but there are only a few things—albeit critically important things—that we can do about the third. Unfortunately, the third factor may turn out to be most important, and ultimately it may override the other two.

In the last fifteen years, researchers have learned that the way we frame events in our minds crucially shapes how we respond to these events. In the wake of the 9/11 attacks, many New Yorkers were terrified. Little was known about the attackers or their methods and capabilities. So people filled in the blanks and jumped to the conclusion that their lives and the city as a whole were in imminent mortal danger. Across the country, the attacks primed Americans to interpret the small number of anthrax letters that were later sent through the postal system as the precursor of a devastating bio-weapon attack. The result was near hysteria, as people besieged their doctors for antibiotics and buildings were evacuated at the sight of anything resembling a white powder. Because people had framed the danger in such extreme terms, another terrorist strike in New York in late 2001—an attack on the scale of 9/11 or larger—would likely have caused huge numbers of people to leave the city.

The same could happen in London if the current attacks continue and escalate in severity, and if the attacks are framed in the wrong way. News reports on Thursday’s bombings indicate that Londoners didn’t respond with the calmness they’d shown two weeks previously. “Witnesses spoke of a panic,” The New York Times reports, “after passengers smelled something burning on one subway car and rushed onto another to escape it, abandoning bags and shoes.”

Many experts on terrorism say we need to learn a lesson from Israel—a society that frames terrorist attacks as horrible but nonetheless manageable instances of chronic, low-level conflict. Even at the height of the suicide bombings in Israel, the country’s citizens for the most part went about their daily lives. The attacks led Israelis to adopt a range of procedures to protect themselves—they inspect bags at the entrances to restaurants and nightclubs, for example—but the attacks weren’t showstoppers and they didn’t induce panic, because most Israelis didn’t frame them as a cataclysmic threat.

The second thing that’s increasing our vulnerability to terrorism is the rising brittleness of many systems critical to our well-being.  Our financial systems, manufacturing industries, transportation networks, information systems, and energy grids are, in some cases, extremely susceptible to attack.  Some of these systems have critical “chokepoints”—like a key tunnel in a subway system or a high-voltage line in an electrical grid—where flows of people, materials, or energy can be easily disrupted. Also, in our endless quest to maximize efficiency and to squeeze out the last bit of waste, we’ve reduced inventories, buffering capacity, and slack within all our economic and technological systems. We’ve made them “tightly coupled,” to use the jargon of systems analysts. At the same time, our demand for services from these systems has soared—as we’ve seen with our hunger for electricity. This combination of factors sharply boosts the risk of cascading breakdowns.

People in southern Ontario had a rude introduction to such brittleness during the blackout in August 2003.  We learned that, especially in our cities, we’ve become so specialized in our abilities and so dependent on complex systems for survival that when things go wrong—when portable phones, ATMs, water systems, subways, traffic lights, and the Web stop working—we can quickly find ourselves in desperate straits. If the blackout had lasted for a couple of days, instead of only ten hours or so in the city core, the situation could have become grim, especially for seniors living in condominium high-rises. Many of these buildings are thirty or more stories high, and some don’t have windows that open. With the power off, many residents had no elevators, air conditioning, or water.  After a couple of days of 35-degree temperatures, we would have been taking some of them out in body bags.

There’s much we can do to increase the resilience of our cities and societies in the face of sudden shock—by loosening coupling within critical systems, increasing inventories (which means reducing our reliance on just-in-time production), and making it possible for individuals to help themselves when systems break down. But almost without exception, we aren’t doing these things. So, despite the lesson of the blackout, and even though we’ve been warned that Ontario faces a critical electricity supply shortfall in coming years—a shortfall that makes repeated brownouts and blackouts more likely—few if any high-rises are being fitted with standby generators.

The third thing that’s increasing our vulnerability is the rising power of terrorists to hurt us. Londoners were lucky that the recent attackers used only conventional explosives. They were also lucky that—in the case of Thursday’s attack—the terrorists were apparently incompetent. But our luck won’t last forever, especially given the rapid diffusion of knowledge about how to make devices that can kill large numbers of people. Most experts believe that sooner or later, a terrorist group will succeed in using a nonconventional biological, chemical, radiological, or nuclear device.

The most appalling possibility is, of course, the detonation of a nuclear bomb in major city. Even a relatively small nuclear explosion would do catastrophic damage. It’s hard to make such a bomb, so the probability of this kind of attack is low, perhaps very low. But it’s still vitally important for nations to gather up and render unusable the world’s huge stockpile of fissile material, especially highly enriched uranium, much of it sitting in insecure facilities in the Former Soviet Union.

As long as terrorists continue to use conventional weapons, our best response is to frame the danger appropriately—these attacks are not a mortal threat, and they don’t pose a great risk to any one individual. We can adapt to the risk, as we go about the tasks of tracking down and eliminating the perpetrators and making sure our vital infrastructure and technological systems are more resilient. But if and when terrorists start using non-conventional weapons, these responses won’t be enough.

And if terrorists get hold of the bomb, it could well be game over: it’s hard to imagine how Western societies could sustain their liberties, institutions, and economic vigor in the face of such a threat. We should be doing everything we can to make sure it never happens.

I’m absolutely delighted to be with you this evening. I’m delighted because this occasion gives me a terrific opportunity to present the argument of my next book, which is tentatively titled: Synchronous Failure: The Real Danger of the 21st Century. The book will sketch out a vision of the future — one that is, I believe, distinct from, and in some cases radically at odds with, the visions that currently prevail in the media and public-policy discourse.

I say “vision,” because prediction is impossible. We can’t possibly know the future’s precise contours. Human affairs are too sensitive to serendipity and chance, to fad, to the whims of leadership, and to the unexpected advent of new technologies. Within our complex and turbulent social, technological, and ecological systems, small events can have macro consequences, while big events can turn out to have far less consequence than we anticipated.

The desire to predict our future dies hard, however, so it’s worth reflecting, for a moment, on just how woefully wrong most attempts at precise prediction are. Let’s look at the track record of technological prediction. In my recent book The Ingenuity Gap, I tell an interesting story about one prominent attempt. In 1967, two of the world’s most competent futurists, Herman Kahn and Anthony Wiener of the Hudson Institute, released a set of predictions of year-2000 technologies, as part of a project undertaken by the American Academy of Arts and Sciences.

Kahn and Weiner listed one hundred technological innovations that would — to quote them — “almost certainly occur.” Some they got right: they foresaw video-players, automated banking systems, and the use of high-altitude cameras for mapping and land use investigations.

But many of their projections were wrong, sometimes laughably wrong: Kahn and Wiener anticipated the widespread use of nuclear explosives for excavation and mining, of robots “slaved” to humans, of large-scale desalinization, and, most remarkably, of “inexpensive and reasonably effective” systems for defending against ballistic missile attack. They also missed some of today’s key technologies entirely, including personal computers, video games, and the World Wide Web. Overall, despite their self-assurance and sense of certainty, their success rate was about 30 percent.

If we’re not very good at predicting the direction and nature of technological change, we are even worse at predicting major social and ecological changes. Thirty years ago who anticipated the fall of the Soviet Union, the collapse of the seemingly infinite Grand Banks cod fishery, the development of AIDs, or the opening up of a vast hole in the stratospheric ozone layer over the Antarctic?

Prediction is a tough business. We generally rely too heavily on linear projections of incremental change in technologies and social arrangements. We are almost hopeless when it comes to anticipating the sharp, sudden non-linear changes that regularly punctuate human affairs.

You try it. Try to come up with a plausible scenario for what this world will look like in, say, 2025 or 2030. After a moment’s reflection, you’ll realize that the range of possibilities is almost infinite and that, given the rate of change in technology and human affairs, there’s something profoundly unknowable about the future, even a future that may arrive well within our lifetimes.

When such a range of possibilities is open, there is little constraint on our underlying biases. Personal temperament, that tendency — deeply embedded in our personalities — towards optimism or pessimism, starts to dominate.

Well-grounded psychological and social-psychological research shows that human beings have, on average, an optimistic bias when it comes to assessing both threats and our efficacy in response to those threats. In other words, we tend to underestimate the risks or threats in our surroundings, and we tend to overestimate our ability to respond to those threats.

This hard-wired optimism, which is the root of our capacity for hope even in the direst circumstances, has enabled our species to overcome extraordinary challenges and to come to dominate this planet.

So as prognosticators, we come hard against two formidable obstacles: the systems we are embedded in are too non-linear and turbulent for precise prediction, and we can’t free ourselves of the biases of temperament.

But we can still, I believe, sketch a vision of the future. Such a vision must be derived from clear assumptions about the deep trends and forces that will shape humankind’s path and that will define the general boundaries within which our precise future will lie. We may not know exactly what things will look like, but we can have an intuition about what is probable and what is wholly unlikely. And it is this kind of vision that I’ll try to provide to you this evening.

I have, in some respects, a pretty grim vision. While most commentators see a future of broadened and deepened global capitalism, of widening democracy and respect for human rights, and of steady – and liberating – progress in science and technology, I believe that the next one hundred years will be a time of great instability and, quite likely, of extraordinary violence and human hardship.

Humankind is creating economic, social, technological, and ecological systems that are planetary in scope. This is the true character of “globalization.” It’s not only about greater economic interdependence. It’s a much broader phenomenon — a relentless increase in the connectedness, complexity, pace, and scope of all humankind’s activities.

The systems we’ve created and now live within are often tightly linked in ways we don’t remotely understand. Taken together, they are potentially highly unstable. They include an international financial system prone to flip between stable and turbulent modes, a perturbed climate that may be on the cusp of dramatically new patterns of behavior, and a global political-economic regime that’s generating immense stresses and potential for mass violence.

Many of the challenges our species now faces are unlike anything we’ve confronted in the past. Never before have we being able to disrupt the fundamental processes of Earth’s climate and ecology; and never before have we created economic, technological and social systems – from continent-wide industrial agriculture to the international financial system – with the enormous connectedness, complexity, and speed of operation that we see around us today.

Whether we are talking about new antibiotic resistant diseases or shiploads of migrants from poor countries dumped on our shores, the problems that we face spill across geographical and intellectual boundaries, their intricacies often exceed our wildest imaginations, and they converge and intertwine in totally unexpected ways.

Humankind, I argue, is on the cusp of a planetary emergency. We face an ever-greater risk of a synchronous failure of our social, economic and biophysical systems, arising from simultaneous, interacting stresses acting powerfully at multiple levels of these global systems.

In reflecting on this vision of the future, I’ve probed my own temperament a lot recently, asking why I have such a deep sense of foreboding about where we’re heading as a species. If anything, this has now biased me against jumping to pessimistic conclusions.

Certainly, we must all acknowledge that many things are going very well in the world today. On average around the world, people are living far longer, healthier, and happier lives then they were even a generation ago. A larger proportion of the human population is living in democracies than ever before. Market-based economic policies are now accepted around the world. There is a general concert of views among the great powers. The spectre of nuclear cataclysm has largely vanished. In many ways, this is the best of times.

And yet . . . and yet, something tells me that this positive story is far from complete. I keep coming back to another set of unassailable facts. These are facts about a formidable array of powerful, underlying pressures — what I’ve come to call “tectonic stresses” – building beneath the superficial activity and buzz of human affairs. Many of these tectonic stresses are not clearly visible on a day-to-day basis for those of us in rich countries. Yet they are nonetheless growing in force, and there’s a risk that they are becoming interconnected and self-reinforcing in a way that could eventually overwhelm the adaptive capacity of our societies.

What are these deep stresses? I’ll identify five that are particularly powerful, and I’ll also identify two additional factors that powerfully multiply the effect of the five stresses. Given my time limitations this evening, I’ll discuss each of these seven factors only briefly. Nevertheless, we should keep in mind that not one of them is being effectively managed at the moment, and any one could cause global society immense hardship in coming decades.

Many of these tectonic stresses are, it might be said, existential — they are directly related to, or affect, the biophysical substrate of human existence on this planet. The first is human population growth and the demographic imbalances that this growth is producing around world.

By the time our population stabilizes, we will see, almost certainly, at least 50 percent further growth from the current 6 billion. We will see, in fact, as much absolute growth in the next fifty years — about three billion people will be added to the world’s population — as we saw in the last 40 years. Conservative commentators are wrong: the population explosion is not over, by any means; indeed, we are probably just past its halfway point.

Ninety-five percent of the future growth will occur in poor countries. It sustains a destabilizing youth bulge in many of these countries’ populations. In some countries in Africa, over 50 percent of the population is below 15 years of age. The youth bulge, in turn, produces large numbers of urbanized, unemployed, young males — the most dangerous social group of all, and the most easily recruited to radical political causes.

Of particular concern are differential rates of growth between regions, especially between the world’s rich and poor regions. These are most noticeable at the interfaces between these regions, such as the boundary between Europe and Africa.

In 1900, Africa’s population was about one-third that of Europe. In 2000, the populations of the regions were roughly equal. By 2050, Africa’s population will be three times that of Europe.

Already we are seeing bodies washing up on the shores of Spain as thousands of migrants try to cross the perilous Straits of Gibraltar, and we’re seeing riots outside the French entrance to the Chunnel train system to Britain. Rich countries have experienced only a tiny fraction of the migration pressures they will experience in coming decades.

The second tectonic stress is the rising capacity of humanity to fundamentally perturb its natural environment and Earth’s biogeochemical systems.

At the micro or local level, this capacity is seen in greater scarcities of renewable resources — such as fresh water, cropland, forests, and fish stocks — for the three billion people on the planet who directly dependent on these resources for their day-to-day livelihood.

These scarcities are caused, in part, by population growth; but they are also due to the interacting influence of other factors — such as failed markets and governments.

By 2025, two-thirds of the world’s population will live in water-scarce regions; about one-third will face severe water shortages.

Overgrazing, erosion, and salinization of cropland, and loss of soil nutrients, already affect tens of millions of hectares of vital agricultural land in poor countries around world.

Forests are important because they maintain and stabilize hydrological cycles. Moreover, sixty percent of the world’s population depends on traditional fuels — charcoal, wood, straw, or cow dung — as a principal energy source. For 40 percent, some 2.5 billion people, it’s their only energy source. Yet currently virgin tropical forests are disappearing a rate of around 15 million hectares per year or 0.5 to 1 percent of the world’s total. While this rate might not seem extreme, the forest loss is highly concentrated in certain countries — including Brazil, Indonesia, and Malaysia — with severe effects on local populations.

And regarding fish supplies, according to latest statistics,  the situation is far worse than previously thought. It turns out that China has been grossly overstating its catches for many years, which means that total global landings probably started to decline some time ago. Well over half the world’s fisheries are over fished or severely over fished (and in a state of collapse), which critically affects the 1 to 1.5 billion people who depend on these stocks for their main source of protein.

All of these changes in the availability of water, cropland, forest, and fish affect the ability of people in poor countries to feed themselves and fundamentally affect their prospects for economic development.

On the macro or global level, examples of the human capacity to perturb biogeochemical systems can be found in the doubling of the flux of reactive nitrogen in the biosphere (because of our use artificial fertilizers), in the thinning of the ozone layer, and in climate change.

I’m going to talk about climate change for a moment. There is evidence, most notably in high latitudes, that climate changes are starting to occur very quickly. The signal of human-induced warming appears to be emerging from the noise of regular climate variations. For example, upward-scanning sonar used by the American military to determine the thickness of Arctic ice shows that the icepack has thinned by about 40 percent in the last 40 years. The average thickness is now about 2 meters, and the thinning appears to be continuing at the rate of about a tenth of a meter every year.

Straightline extrapolation suggests that we could see in three decades or so the appearance of wide swathes of open water in the Arctic. Given that open water absorbs about 80 percent more solar energy than sea ice, this development alone could change the energy balance for the whole northern part of the planet.

But straightline extrapolation is a dangerous game in the climate business. One thing that we do know is that climate change, if it occurs, will likely come in sharp, nonlinear jumps — a form of change that human societies have great difficulty anticipating or adapting to.

Furthermore, the costs of climate change will be disproportionately borne by those who can least afford them, especially those in poor regions and areas of marginal agricultural productivity. Rapid climate change produces adjustment problems, and poor societies are least able to keep up.

The third tectonic stress is the critical problem of energy supply – especially of hydrocarbons – for a rapidly growing world economy.

There is still a lot of oil and natural gas around — although reserve estimates for many countries have almost certainly been inflated for economic and political reasons. But the most abundant, easiest to extract, and cheapest pools of hydrocarbons have already been found, and their production is starting to decline (in some areas, like continental United States, this decline is well-advanced). Meanwhile, alternative or new pools are far more expensive, smaller in size, dirtier (for example, oil shales and tar sands) and located in geopolitically unstable regions.

The fourth stress is disease. Although not readily apparent to those of us in rich countries, the world is facing ferocious pandemics of tuberculosis and AIDS. Tuberculosis, the top killer among infectious diseases, had infected nearly a third of the human population; it kills three million people year (a remarkable 5 percent of total deaths from all causes), and its incidence is growing fast.

AIDS has devastated the economies and military and civil infrastructures of many sub-Saharan African countries. It is literally eating the guts out of these societies. And AIDS is now making rapid inroads in India and China. While there has been recent grudging acknowledgment of the danger of AIDS in China, the problem has received little official attention in India. Let’s be clear, though, about the implications: even if the infection rate peaks in these countries at 10 percent — which is only 1/2 to 1/3 of what we’re seeing in southern Africa currently — we would be looking at 200 million infected people in two countries alone, with incalculable consequences for the development of the world’s largest Southern economies.

But we should not just be concerned about AIDS and tuberculosis and other well-known and widespread diseases. As the transportation and trade networks of global society have been extended into the smallest and most distant niches of the planet’s ecological systems, the rate of appearance of new, unheard of diseases has risen dramatically. Pathogens that previously inhabited only  localized human populations — populations immune to the pathogens’ effects — now have access to the whole human species. And we should keep in mind that the human species is now the second biggest mass of genetically identical organic material on the planet (after the mass of krill in the Antarctic) — an extraordinarily rich and densely connected environment for the spread of disease.

The fifth stress is the widening wealth gap between  rich and poor around the planet. U.N. data suggest that this gap has, in crude terms, roughly doubled in size in the last 40 years. In 1960, the income of the richest 20 percent of the world’s population was 30 times that of the poorest 20 percent; today, it’s over 80 times greater. Research shows that highly unequal societies tend to be violent. Humankind is creating a grotesquely and increasingly unequal global society, and we can expect it to be increasingly violent.

The world economy is a mess, and critical economic policymakers – such as the heads of national central banks, the IMF, and the World Bank – seem flummoxed. Many of the richest economies are stagnating, while in poor countries nearly half the world’s population still lives on less than $2 a day.

The U.S. economy – critical to world growth – is, in many respects, sliding sideways. European growth is also almost nonexistent, and Germany’s unemployment rate is nearing double digits. The Japanese Nikkei Index has dropped to levels unseen in two decades, with renewed doubts about the stability of the country’s banking system. Latin America is in financial crisis; a decade of market liberalization on the continent has produced growth rates half those of the ’60s and a rise in the number of poor people. Turkey’s economy is in shambles. And Africa . . . well, Africa and its 700 million inhabitants aren’t even on the economic map.

Through larger markets and the rising importance of ideas for the production of wealth, we are creating a global winner-take-all economy. The global economy also suffers from chronic overproduction relative to consumption: at the moment, the world probably has 30 to 40 percent excess productive capacity.

Put simply, global capitalism is superb at producing vast amounts of stuff but nowhere near as good at generating sufficient demand for that stuff. Relative to the level of demand, there are too many factories, farms, mines, airliners, hotels, book publishers, and the like. In fact, global capitalism’s relentless “creative destruction” – the constant churning of technological change that overturns corporations and repeatedly throws people out of work – often erodes the very consumer demand that capitalism desperately needs to sustain itself.

In a tightly integrated global economy characterized by inadequate demand, a country’s economic policy must emphasize – first and foremost – competitiveness. As if caught on an ever-faster treadmill, policymakers must race to make their own country’s economy more efficient, more productive, and more nimble than all the rest. If their country succeeds in producing its goods and services more cheaply than its competitors, it will capture a sizable slice of available demand. If not, it will probably be left far behind.

In this environment, poor and weaker societies increasingly feel penetrated by globalized Western markets and culture, and this causes widespread resentment. In general, widening gulfs of wealth and opportunity mean that vast populations around world have chronically unsatisfied expectations.

The destabilizing social, economic, and political effects of these five tectonic stresses are powerfully boosted by two other factors — factors that I call “multipliers.” The first of these is the rising complexity, connectedness, and velocity of human technologies, institutions, and social interactions.

Over a century ago, the French sociologist Emile Durkheim referred to this as the rising “dynamic density” of human societies. In contemporary terms, I use this concept to refer to the rapidly growing number of entities or nodes in the complex technological, social, and economic networks we create around us; the rapid increase in the density of linkages among these nodes; and the truly exponential increase in the rate at which we are moving material, energy, people, and especially information across those links. This increase in connectedness and interdependence produces many benefits, but it can also result in unexpected system behavior, including cascade effects as damage in one part of a global network — whether caused by a new pathogen, a computer virus, or a financial shock — multiplies and spreads rapidly to other parts of the network.

Good examples of such destabilizing cascades in the international economy include the Mexican peso crisis in 1994 and the Asian crisis of 1997 and 1998. The world economy is increasingly volatile in its overall behavior: as modern communication technologies tighten the coupling and increase the pace of transactions within international markets, the international financial system is becoming more prone to sharply nonlinear, boom-bust cycles, to sudden shifts between stable and turbulent modes, and to contagion effects, as a crisis in one national economy cascades outwards to affect others.

The second multiplier is the relentlessly escalating power of individuals and sub-groups – like terrorists and insurgents – to destroy things and people.

Put bluntly, the bad guys are getting stronger, fast. They have better weapons: the trend over the centuries has been towards unremitting improvement in the lethality of all weaponry, which generally has meant that steadily fewer people could kill steadily larger numbers of people more quickly than ever before. In particular, small arms and light weapons – such as assault rifles, rocket propelled grenades, mortars and the like – have become more lethal as their technology has advanced. They have become more rugged, cheaper, more portable, easier to use, and more accurate, and their striking range has increased. The result is extraordinary and unprecedented technological leverage. Now, as we’ve seen recently in this city, two people with one sniper’s rifle can terrorize several million people for weeks.

Violent small groups will achieve their ultimate technological leverage when they obtain weapons of mass destruction. Notice I say when, not if. I’m not being a wide-eyed alarmist here — the best people in the business of analyzing this threat, believe the risk of nuclear terrorism, especially, is very real. The world now harbors in excess of 1000 tons of uranium 235, much of it stored in scattered and insecure locations in the former Soviet Union. With sufficient skill it takes only 50 kilograms to make a crude atomic device. If a terrorist can obtain 100 kilograms, less than one hundredth of a percent of the total world stockpile, little skill is needed: with such a quantity, it’s relatively easy to create an explosion in the multi-kiloton range. Cities like this one are very likely targets.

In addition, terrorists and other violent groups have vastly improved access to sources of information through the Internet and the Web, and they can use these new communication technologies to better coordinate their attacks and organize themselves. A standard laptop now has computational power comparable to that available to the entire US Defense Department in the 1960s. This power allows violent groups to use state-of-the-art encryption technologies to hide their communication. Excellent encryption technologies are widely available as free-ware on the Web.

Violent groups will soon recognize the rewards from attacking non-redundant, high-value nodes in our increasingly complex technological and economic networks. These attacks will be intended to precipitate cascades of failures or the collapse of whole technological and social systems. They will also take advantage of the tendency of modern societies to concentrate high-value assets – especially skilled people and advanced equipment – in relatively small geographic locations, like the World Trade Center. And they will learn how to divert powerful, non-weapons technologies to destructive ends — like ramming airliners into skyscrapers. Once terrorists look around, they will find that our rich, technologically advanced, and complex societies are replete with supercharged devices — packed with energy, combustibles, and explosives — that can be quite easily diverted or hijacked for hostile ends.

These, then, are the seven factors — five tectonic stresses and two multipliers — that will powerfully influence the trajectory of human development over the next century. The bottom line of the preceding analysis is the following: Demographic, environmental, technological, and economic pressures are producing two outcomes that have immense implications for global political stability. First, these pressures are contributing to social upheaval, dislocation, and unmet expectations that boost the grievances of a large fraction of the human population. Second, by undermining the capacity of governments and states, these pressures also boost opportunities for violence by aggrieved groups. In short, they produce exploitable resentments, political instabilities, and radicalized societies.

People often get angry when they see around them wide gaps of wealth and opportunity. If they identify with a group on the losing side of one of those gaps, it can lead to a sense of humiliation and a profound sense of one’s group having been disrespected. These resentments are ready for exploitation by megalomaniacs like Osama bin Laden. We now live in a world brimming with such righteous causes.

There are, as a result, greater numbers of very angry and sometimes fanatical people around; these people are more mobile than ever before; and some of them are willing to sacrifice their lives to destroy those groups and people they believe are the source of the world’s injustice.

The capability of violent groups to launch such attacks is rising very fast. Soon, perhaps very soon, small groups of people will be able to humble whole nations. We haven’t even begun to think through what this means for our institutions, our economies, and our democracies.

But the argument I’ve made to this point actually understates the severity of the challenge we face. By discussing sequentially these seven factors that threaten humankind’s future – and by treating them as discrete and isolatable – I haven’t given enough weight to the critical fact that all these pressures are developing at the same time. Change of an unprecedented rate and magnitude is happening simultaneously
in a wide range of domains critical to our well being. It’s as if humankind has its collective foot slammed down on the world’s accelerator pedal. And it’s this simultaneity of events that’s at the heart of my concern about synchronous failure.

At the same time that water, cropland, and forest resources are critically overstretched in many regions, we are causing major changes in the planet’s climate that accentuate the impacts of these resource shortages. At the same time that global energy supplies are increasingly concentrated in some of the planet’s most dangerous and politically unstable zones, the world economy needs cheap energy more than ever to maintain its fitful growth. At the same time that we need to boost global consumption to keep the world economy from slipping into a deflationary spiral, we are confronted by ever more abundant evidence that our current consumption is already severely overloading the absorptive capacity and resilience of the planet’s biosphere. And at the same time that yawning gaps of wealth and power are developing within the human population, technological developments have put staggering destructive power in the hands of small groups that may be angered by those gaps.

We aren’t thinking in terms of simultaneity, because we tend to “silo” our problems. We treat our challenges — from climate change to international economic instability to terrorism — in isolation, and we tend not to see the whole picture. But the simultaneity of pressures in our world presents two dangers. First, key institutions at the global and national levels may simply be overwhelmed by the rush of events; these institutions may not be able to stay on top of, let alone manage, the tangled and converging pressures they face. The second danger of simultaneity is that several of the tectonic stresses I’ve described will reach a crisis point at the same time, causing entirely unpredictable cascades of failure through our tightly coupled and hyper-complex global systems.

For instance, what happens if the following three events occur together or in quick succession? A sharp shift in climate that cripples food production and destabilizes regimes across Asia; a major international financial crisis that sends currencies and markets tumbling around the world; and a string of terrorist attacks – costing tens of thousands of lives – on several Western capital cities. Although we can’t estimate the exact probability of any one of these events, we can say with reasonable confidence  that their individual probabilities are rising. The probability of their joint occurrence is, of course, much lower, but we can be sure that it’s rising too, especially if – as is likely – these three events are not causally independent of each other. And this is only one scenario of an uncountable number of possible combinations of the seven factors I’ve identified. Indeed, if some form of synchronous failure does occur, it’s likely that it will occur in a way that we’ve never anticipated, because the range of possibilities is almost infinite. We shouldn’t be surprised by surprise.

Such a convergence of events as I’ve described – climate shift, financial crisis, and mega-terrorist attacks – could overwhelm the adaptive capacity and resilience of even the richest and most powerful societies. A breakdown of global institutional and social order might then happen very suddenly — essentially “out of the blue.” It could be completely unexpected, because the pressures I’ve identified – demographic, environment, economic, and the like – will have been building under the surface for a long time, quietly eroding the resilience of our national and global systems. When they eventually converge and climax, there may be little adaptive capacity left to absorb the shock.

I come to this conclusion in part because of recent research into the causes of major social revolutions, like the French and Russian revolutions. This research shows that social breakdown occurs when societies are under multiple stresses at many social levels simultaneously. As, Jack Goldstone, one of the world’s leading theorists of revolution writes: “Massive state breakdown is likely to occur only when there are simultaneously high levels of distress and conflict at several levels of society – in the state, among elites, and in the populace.”¹ This is the condition we’re now creating at the global level.

It’s easy to dismiss or pigeonhole this kind of argument as ridiculously alarmist. Here’s where temperament comes in, once again. To be frank, I hope I’m wrong in my analysis, but the evidence of the seven driving factors I’ve identified here this evening is strong.

Perhaps the chance of the convergence of these factors in the next decades is low — who knows, maybe it’s no more than 5,10, or 15 percent — but the costs to human society would be immense if something like this were to occur. The possibility, I believe, needs to be taken very seriously.

So what should we do? What are some possible policies or plans to prevent such an outcome?

I believe it’s entirely within human ability to prevent any form of synchronous failure. There is much that we can do, and at least a quarter of my coming book will be devoted to policy prescriptions.

We must first recognize, though, that for the first time in our species’ history, we have to be aggressively proactive on multiple fronts simultaneously. Each of the five tectonic stresses and two multipliers I’ve identified requires its own policy responses. There’s no magic bullet, no single solution or institutional response that will cover all these problems.

We need to be increasing, not decreasing, our support for worldwide family planning; we need to boost efforts around the planet in soil, forest, and water conservation; we need to take climate change far more seriously and begin planning for a global transition to a suite of new energy technologies (including carbon sequestration, geologic storage, and hydrogen power) that will dramatically reduce our carbon emissions; we need to work out reasonable protection for intellectual property rights and then get antiretroviral drugs into the hands of the millions of people infected with AIDS around the world; we need to reform the international financial system so that it no longer wrecks the economies of major countries like Indonesia and Argentina in response to the corrupt economic policies of their elites.

We also need to reduce the vulnerability of our complex economic and technological systems to cascade effects and nonlinear failures. This may require a radically different way of thinking about economic development and globalization. Sometimes the best policies may not be those that increase integration, interconnectedness, speed, and efficiency. Sometimes, in order to boost overall system resilience, it might be necessary to loosen the coupling within our economic and technological systems, for instance by making greater use of decentralized, local energy and food production, and by slowing the connection speed between system components, so that people have time to think before they act. And it might be necessary to increase buffering capacity of these systems, for instance by moving away from just-in-time production processes and by increasing inventories of feed stocks and parts for our factories.

It’s on the matter of the increasing destructive power of small groups that I have most difficulty providing clear prescriptions. This multiplier is driven by technological trends that we can’t derail without doing extraordinary damage to our overall economic progress, because the technologies that terrorists use – like laptop computers and the Internet – are often the same ones we use on a day-to-day basis.

To lower our vulnerability to attack, we will have to consider, in coming years, dispersing our high-value assets – in 100 years, skyscrapers may seem like quaint anachronisms. But we also have to recognize that the war on terrorism is not a war in any conventional sense. It’s more like a worldwide guerrilla conflict, in which the enemy chooses where to strike and then disappears into a vast crowd of passive supporters. I’m not sure that the US, given the way it has defined this conflict, can win this war – because the US has defined for itself an essentially infinite security frontier, from nightclubs in Bali to resorts in Mombassa.

Yet as we try to prepare for the future’s broader challenges – not just the challenge of terrorism – our first step must be to recognize and better understand the diverse nature of these challenges – their true scope, character and urgency, and, most importantly, the relationships among them. Just because things look like they’re going well on the surface, as they do to many people in America now, it doesn’t mean that things are actually going well underneath.

Much of our thinking about the future should be “out of the box” scenario development, which explicitly involves trying to move beyond the linear extrapolation of current trends.

Since we can’t possibly know exactly how things will turn out in coming decades, or exactly when sharp social, economic, or ecological nonlinearities will occur, we need to develop in advance strategies for response and adaptation to multiple contingencies. In other words, when nasty surprises occur, which they sometimes will, we will be much better off if we have contingency plans “on the shelf” and ready to go.

We especially need ideas on how to build governance capacity at the national and global levels, because – most fundamentally — the challenges we face are about the provision of public goods — like health infrastructure, well-functioning markets, protection of our common environment, and security from violence. The adequate provision of public goods requires capable institutions of governance.

Interdisciplinary research is key here – we need to get the demographers, energy specialists, and climate scientists talking to the agronomists, political scientists, and economists. But interdisciplinary research is something we don’t do well, because of turf battles among disciplines, institutions that reinforce disciplinary boundaries (especially the system of disciplinary journals), and lack of funding.

We are clearly faced with immense political and intellectual tasks – in public policy, in public education and mobilization, and in scientific research. We need to be investing vastly greater resources in these areas. But if we’re prepared to invest the necessary resources, and if we are prepared to back the right policies with the necessary political will, I’m convinced that my vision of synchronous failure will never be realized.

Thank you.

¹ Jack Goldstone, Revolution and Rebellion in the Early Modern World (Berkeley: University of California Press, 1991), p. 469.

Modern societies face a cruel paradox: Fast-paced technological and economic innovations may deliver unrivalled prosperity, but they also render rich nations vulnerable to crippling, unanticipated attacks. By relying on intricate networks and concentrating vital assets in small geographic clusters, advanced Western nations only amplify the destructive power of terrorists and the psychological and financial damage they can inflict.

It’s 4 a.m. on a sweltering summer night in July 2003. Across much of the United States, power plants are working full tilt to generate electricity for millions of air conditioners that are keeping a ferocious heat wave at bay. The electricity grid in California has repeatedly buckled under the strain, with rotating blackouts from San Diego to Santa Rosa.

In different parts of the state, half a dozen small groups of men and women gather. Each travels in a rented minivan to its prearranged destination—for some, a location outside one of the hundreds of electrical substations dotting the state; for others, a spot upwind from key, high-voltage transmission lines. The groups unload their equipment from the vans. Those outside the substations put together simple mortars made from materials bought at local hardware stores, while those near the transmission lines use helium to inflate weather balloons with long silvery tails. At a precisely coordinated moment, the homemade mortars are fired, sending showers of aluminum chaff over the substations. The balloons are released and drift into the transmission lines.

Simultaneously, other groups are doing the same thing along the Eastern Seaboard and in the South and Southwest. A national electrical system already under immense strain is massively short-circuited, causing a cascade of power failures across the country. Traffic lights shut off. Water and sewage systems are disabled. Communications systems break down. The financial system and national economy come screeching to a halt.

Sound far-fetched? Perhaps it would have before September 11, 2001, but certainly not now. We’ve realized, belatedly, that our societies are wide-open targets for terrorists. We’re easy prey because of two key trends: First, the growing technological capacity of small groups and individuals to destroy things and people; and, second, the increasing vulnerability of our economic and technological systems to carefully aimed attacks. While commentators have devoted considerable ink and airtime to the first of these trends, they’ve paid far less attention to the second, and they’ve virtually ignored their combined effect. Together, these two trends facilitate a new and sinister kind of mass violence—a “complex terrorism” that threatens modern, high-tech societies in the world’s most developed nations.

Our fevered, Hollywood-conditioned imaginations encourage us to focus on the sensational possibility of nuclear or biological attacks—attacks that might kill tens of thousands of people in a single strike. These threats certainly deserve attention, but not to the neglect of the likelier and ultimately deadlier disruptions that could result from the clever exploitation by terrorists of our societies’ new and growing complexities.

Weapons of Mass Disruption

The steady increase in the destructive capacity of small groups and individuals is driven largely by three technological advances: more powerful weapons, the dramatic progress in communications and information processing, and more abundant opportunities to divert non-weapon technologies to destructive ends.

Consider first the advances in weapons technology. Over the last century, progress in materials engineering, the chemistry of explosives, and miniaturization of electronics has brought steady improvement in all key weapons characteristics, including accuracy, destructive power, range, portability, ruggedness, ease-of-use, and affordability. Improvements in light weapons are particularly relevant to trends in terrorism and violence by small groups, where the devices of choice include rocket-propelled grenade launchers, machine guns, light mortars, land mines, and cheap assault rifles such as the famed AK-47. The effects of improvements in these weapons are particularly noticeable in developing countries. A few decades ago, a small band of terrorists or insurgents attacking a rural village might have used bolt-action rifles, which take precious time to reload.

Today, cheap assault rifles multiply the possible casualties resulting from such an attack. As technological change makes it easier to kill, societies are more likely to become locked into perpetual cycles of attack and counterattack that render any normal trajectory of political and economic development impossible.

Meanwhile, new communications technologies—from satellite phones to the Internet—allow violent groups to marshal resources and coordinate activities around the planet. Transnational terrorist organizations can use the Internet to share information on weapons and recruiting tactics, arrange surreptitious fund transfers across borders, and plan attacks. These new technologies can also dramatically enhance the reach and power of age-old procedures. Take the ancient hawala system of moving money between countries, widely used in Middle Eastern and Asian societies. The system, which relies on brokers linked together by clan-based networks of trust, has become faster and more effective through the use of the Internet.

Information-processing technologies have also boosted the power of terrorists by allowing them to hide or encrypt their messages. The power of a modern laptop computer today is comparable to the computational power available in the entire U.S. Defense Department in the mid-1960s. Terrorists can use this power to run widely available state-of-the-art encryption software. Sometimes less advanced computer technologies are just as effective. For instance, individuals can use a method called steganography (“hidden writing”) to embed messages into digital photographs or music clips. Posted on publicly available Web sites, the photos or clips are downloaded by collaborators as necessary. (This technique was reportedly used by recently arrested terrorists when they planned to blow up the U.S. Embassy in Paris.) At latest count, 140 easy-to-use steganography tools were available on the Internet. Many other off-the-shelf technologies—such as “spread-spectrum” radios that randomly switch their broadcasting and receiving signals—allow terrorists to obscure their messages and make themselves invisible.

The Web also provides access to critical information. The September 11 terrorists could have found there all the details they needed about the floor plans and design characteristics of the World Trade Center and about how demolition experts use progressive collapse to destroy large buildings. The Web also makes available sets of instructions—or “technical ingenuity”— needed to combine readily available materials in destructive ways. Practically anything an extremist wants to know about kidnapping, bomb making, and assassination is now available online. One somewhat facetious example: It’s possible to convert everyday materials into potentially destructive devices like the “potato cannon.” With a barrel and combustion chamber fashioned from common plastic pipe, and with propane as an explosive propellant, a well-made cannon can hurl a homely spud hundreds of meters—or throw chaff onto electrical substations. A quick search of the Web reveals dozens of sites giving instructions on how to make one.

Finally, modern, high-tech societies are filled with supercharged devices packed with energy, combustibles, and poisons, giving terrorists ample opportunities to divert such non-weapon technologies to destructive ends. To cause horrendous damage, all terrorists must do is figure out how to release this power and let it run wild or, as they did on September 11, take control of this power and retarget it. Indeed, the assaults on New York City and the Pentagon were not low-tech affairs, as is often argued. True, the terrorists used simple box cutters to hijack the planes, but the box cutters were no more than the “keys” that allowed the terrorists to convert a high-tech means of transport into a high-tech weapon of mass destruction. Once the hijackers had used these keys to access and turn on their weapon, they were able to deliver a kiloton of explosive power into the World Trade Center with deadly accuracy.

High-Tech Hubris

The vulnerability of advanced nations stems not only from the greater destructive capacities of terrorists, but also from the increased vulnerability of the West’s economic and technological systems. This additional vulnerability is the product of two key social and technological developments: first, the growing complexity and interconnectedness of our modern societies; and second, the increasing geographic concentration of wealth, human capital, knowledge, and communication links.

Consider the first of these developments. All human societies encompass a multitude of economic and technological systems. We can think of these systems as networks—that is, as sets of nodes and links among those nodes. The U.S. economy consists of numerous nodes, including corporations, factories, and urban centers; it also consists of links among these nodes, such as highways, rail lines, electrical grids, and fiber-optic cables. As societies modernize and become richer, their networks become more complex and interconnected. The number of nodes increases, as does the density of links among the nodes and the speed at which materials, energy, and information are pushed along these links. Moreover, the nodes themselves become more complex as the people who create, operate, and manage them strive for better performance. (For instance, a manufacturing company might improve efficiency by adopting more intricate inventory- control methods.)

Complex and interconnected networks sometimes have features that make their behavior unstable and unpredictable. In particular, they can have feedback loops that produce vicious cycles. A good example is a stock market crash, in which selling drives down prices, which begets more selling. Networks can also be tightly coupled, which means that links among the nodes are short, therefore making it more likely that problems with one node will spread to others. When drivers tailgate at high speeds on freeways, they create a tightly coupled system: A mistake by one driver, or a sudden shock coming from outside the system, such as a deer running across the road, can cause a chain reaction of cars piling onto each other. We’ve seen such knock-on effects in the U.S. electrical, telephone, and air traffic systems, when a failure in one part of the network has sometimes produced a cascade of failures across the country. Finally, in part because of feedbacks and tight coupling, networks often exhibit nonlinear behavior, meaning that a small shock or perturbation to the network produces a disproportionately large disruption.

Terrorists and other malicious individuals can magnify their own disruptive power by exploiting these features of complex and interconnected networks. Consider the archetypal lone, nerdy high-school kid hacking away at his computer in his parents’ basement who can create a computer virus that produces chaos in global communications and data systems. But there’s much more to worry about than just the proliferation of computer viruses. A special investigative commission set up in 1997 by then U.S. President Bill Clinton reported that “growing complexity and interdependence, especially in the energy and communications infrastructures, create an increased possibility that a rather minor and routine disturbance can cascade into a regional outage.” The commission continued: “We are convinced that our vulnerabilities are increasing steadily, that the means to exploit those weaknesses are readily available and that the costs [of launching an attack] continue to drop.”

Terrorists must be clever to exploit these weaknesses. They must attack the right nodes in the right networks. If they don’t, the damage will remain isolated and the overall network will be resilient. Much depends upon the network’s level of redundancy—that is, on the degree to which the damaged node’s functions can be offloaded to undamaged nodes. As terrorists come to recognize the importance of redundancy, their ability to disable complex networks will improve. Langdon Winner, a theorist of politics and technology, provides the first rule of modern terrorism: “Find the critical but nonredundant parts of the system and sabotage … them according to your purposes.” Winner concludes that “the science of complexity awaits a Machiavelli or Clausewitz to make the full range of possibilities clear.”

The range of possible terrorist attacks has expanded due to a second source of organizational vulnerability in modern economies—the rising concentration of high-value assets in geographically small locations. Advanced societies concentrate valuable things and people in order to achieve economies of scale. Companies in capital-intensive industries can usually reduce the per-unit cost of their goods by building larger production facilities. Moreover, placing expensive equipment and highly skilled people in a single location provides easier access, more efficiencies, and synergies that constitute an important source of wealth. That is why we build places like the World Trade Center.

In so doing, however, we also create extraordinarily attractive targets for terrorists, who realize they can cause a huge amount of damage in a single strike. On September 11, a building complex that took seven years to construct collapsed in 90 minutes, obliterating 10 million square feet of office space and exacting at least $30 billion in direct costs. A major telephone switching office was destroyed, another heavily damaged, and important cellular antennas on top of the towers were lost. Key transit lines through southern Manhattan were buried under rubble. Ironically, even a secret office of the U.S. Central Intelligence Agency was destroyed in the attack, temporarily disrupting normal intelligence operations.

Yet despite the horrific damage to the area’s infrastructure and New York City’s economy, the attack did not cause catastrophic failures in U.S. financial, economic, or communications networks. As it turned out, the World Trade Center was not a critical, nonredundant node. At least it wasn’t critical in the way most people (including, probably, the terrorists) would have thought. Many of the financial firms in the destroyed buildings had made contingency plans for disaster by setting up alternate facilities for data, information, and computer equipment in remote locations. Though the NASDAQ headquarters was demolished, for instance, the exchange’s data centers in Connecticut and Maryland remained linked to trading companies through two separate connections that passed through 20 switching centers. NASDAQ officials later claimed that their system was so robust that they could have restarted trading only a few hours after the attack. Some World Trade Center firms had made advanced arrangements with companies specializing in providing emergency relocation facilities in New Jersey and elsewhere. Because of all this proactive planning—and the network redundancy it produced—the September 11 attacks caused remarkably little direct disruption to the U.S. financial system (despite the unprecedented closure of the stock market for several days).

But when we look back years from now, we may recognize that the attacks had a critical effect on another kind of network that we’ve created among ourselves: a tightly coupled, very unstable, and highly nonlinear psychological network. We’re all nodes in this particular network, and the links among us consist of Internet connections, satellite signals, fiber-optic cables, talk radio, and 24-hour television news. In the minutes following the attack, coverage of the story flashed across this network. People then stayed in front of their televisions for hours on end; they viewed and reviewed the awful video clips on the CNN Web site; they plugged phone lines checking on friends and relatives; and they sent each other millions upon millions of e-mail messages— so many, in fact, that the Internet was noticeably slower for days afterwards.

Along these links, from TV and radio stations to their audiences, and especially from person to person through the Internet, flowed raw emotion: grief, anger, horror, disbelief, fear, and hatred. It was as if we’d all been wired into one immense, convulsing, and reverberating neural network. Indeed, the biggest impact of the September 11 attacks wasn’t the direct disruption of financial, economic, communications, or transportation networks—physical stuff, all. Rather, by working through the network we’ve created within and among our heads, the attacks had their biggest impact on our collective psychology and our subjective feelings of security and safety. This network acts like a huge megaphone, vastly amplifying the emotional impact of terrorism.

To maximize this impact, the perpetrators of complex terrorism will carry out their attacks in audacious, unexpected, and even bizarre manners—using methods that are, ideally, unimaginably cruel. By so doing, they will create the impression that anything is possible, which further magnifies fear. From this perspective, the World Trade Center represented an ideal target, because the Twin Towers were an icon of the magnificence and boldness of American capitalism. When they collapsed like a house of cards, in about 15 seconds each, it suggested that American capitalism was a house of cards, too. How could anything so solid and powerful and so much a part of American identity vanish so quickly? And the use of passenger airplanes made matters worse by exploiting our worst fears of flying.

Unfortunately, this emotional response has had huge, real-world consequences. Scared, insecure, grief-stricken people aren’t ebullient consumers. They behave cautiously and save more. Consumer demand drops, corporate investment falls, and economic growth slows. In the end, via the multiplier effect of our technology-amplified emotional response, the September 11 terrorists may have achieved an economic impact far greater than they ever dreamed possible. The total cost of lost economic growth and decreased equity value around the world could exceed a trillion dollars. Since the cost of carrying out the attack itself was probably only a few hundred thousand dollars, we’re looking at an economic multiplier of over a millionfold.

The Weakest Links

Complex terrorism operates like jujitsu—it redirects the energies of our intricate societies against us. Once the basic logic of complex terrorism is understood (and the events of September 11 prove that terrorists are beginning to understand it), we can quickly identify dozens of relatively simple ways to bring modern, high-tech societies to their knees.

How would a Clausewitz of terrorism proceed? He would pinpoint the critical complex networks upon which modern societies depend. They include networks for producing and distributing energy, information, water, and food; the highways, railways, and airports that make up our transportation grid; and our health-care system. Of these, the vulnerability of the food system is particularly alarming. However, terrorism experts have paid the most attention to the energy and information networks, mainly because they so clearly underpin the vitality of modern economies.

The energy system—which comprises everything from the national network of gas pipelines to the electricity grid—is replete with high-value nodes like oil refineries, tank farms, and electrical substations. At times of peak energy demand, this network (and in particular, the electricity grid) is very tightly coupled. The loss of one link in the grid means that the electricity it carries must be offloaded to other links. If other links are already operating near capacity, the additional load can cause them to fail, too, thus displacing their energy to yet other links. We saw this kind of breakdown in August 1996, when the failure of the Big Eddy transmission line in northern Oregon caused overloading on a string of transmission lines down the West Coast of the United States, triggering blackouts that affected 4 million people in nine states.

Substations are clear targets because they represent key nodes linked to many other parts of the electrical network. Substations and high-voltage transmission lines are also “soft” targets, since they can be fairly easily disabled or destroyed. Tens of thousands of miles of transmission lines are strung across North America, often in locations so remote that the lines are almost impossible to protect, but they are nonetheless accessible by four wheel drive. Transmission towers can be brought down with well-placed explosive charges. Imagine a carefully planned sequence of attacks on these lines, with emergency crews and investigators dashing from one remote attack site to another, constantly off-balance and unable to regain control. Detailed maps of locations of substations and transmission lines for much of North America are easily available on the Web. Not even all the police and military personnel in the United States would suffice to provide even rudimentary protection to this immense network.

The energy system also provides countless opportunities for turning supposedly benign technology to destructive ends. For instance, large gas pipelines, many of which run near or even through urban areas, have huge explosive potential; attacks on them could have the twin effect of producing great local damage and wider disruptions in energy supply. And the radioactive waste pools associated with most nuclear reactors are perhaps the most lethal targets in the national energy-supply system. If the waste in these facilities were dispersed into the environment, the results could be catastrophic. Fortunately, such attacks would be technically difficult.

Even beyond energy networks, opportunities to release the destructive power of benign technologies abound. Chemical plants are especially tempting targets, because they are packed with toxins and flammable, even explosive, materials. Security at such facilities is often lax: An April 1999 study of chemical plants in Nevada and West Virginia by the U.S. Agency for Toxic Substances and Disease Registry concluded that security ranged from “fair to very poor” and that oversights were linked to “complacency and lack of awareness of the threat.” And every day, trains carrying tens of thousands of tons of toxic material course along transport corridors throughout the United States. All a terrorist needs is inside knowledge that a chemical-laden train is traveling through an urban area at a specific time, and a well-placed object (like a piece of rail) on the track could cause a wreck, a chemical release, and a mass evacuation. A derailment of such a train at a nonredundant link in the transport system-such as an important tunnel or bridge—could be particularly potent. (In fact, when the U.S. bombing campaign in Afghanistan began on October 7, 2001, the U.S. railroad industry declared a three-day moratorium on transporting dangerous chemicals.) Recent accidents in Switzerland and Baltimore, Maryland, make clear that rail and highway tunnels are vulnerable because they are choke points for transportation networks and because it’s extraordinarily hard to extinguish explosions and fires inside them.

Modern communications networks also are susceptible to terrorist attacks. Although the Internet was originally designed to keep working even if large chunks of the network were lost (as might happen in a nuclear war, for instance), today’s Internet displays some striking vulnerabilities. One of the most significant is the system of computers—called “routers” and “root servers”— that directs traffic around the Net. Routers represent critical nodes in the network and depend on each other for details on where to send packets of information. A software error in one router, or its malicious reprogramming by a hacker, can lead to errors throughout the Internet. Hackers could also exploit new peer-to-peer software (such as the information-transfer tool Gnutella) to distribute throughout the Internet millions of “sleeper” viruses programmed to attack specific machines or the network itself at a predetermined date.

The U.S. government is aware of many of these threats and of the specific vulnerability of complex networks, especially information networks. President George W. Bush has appointed Richard Clarke, a career civil servant and senior advisor to the National Security Council on counter-terrorism, as his cyberspace security czar, reporting both to Director of Homeland Security Tom Ridge and National Security Advisor Condoleezza Rice. In addition, the U.S. Senate recently considered new legislation (the Critical Infrastructure Information Security Act) addressing a major obstacle to improved security of critical networks: the understandable reluctance of firms to share proprietary information about networks they have built or manage. The act would enable the sharing of sensitive infrastructure information between the federal government and private sector and within the private sector itself. In his opening remarks to introduce the act on September 25, 2001, Republican Sen. Bob Bennett of Utah clearly recognized that we face a new kind of threat. “The American economy is a highly interdependent system of systems, with physical and cyber components,” he declared. “Security in a networked world must be a shared responsibility.”

Preparing for the Unknown

Shortly following the September 11 attacks, the U.S. Army enlisted the help of some of Hollywood’s top action screenwriters and directors—including the writers of Die Hard and McGyver—to conjure up possible scenarios for future terrorist attacks. Yet no one can possibly imagine in advance all the novel opportunities for terrorism provided by our technological and economic systems. We’ve made these critical systems so complex that they are replete with vulnerabilities that are very hard to anticipate, because we don’t even know how to ask the right questions. We can think of these possibilities as “exploitable unknown unknowns.” Terrorists can make connections between components of complex systems—such as between passenger airliners and skyscrapers—that few, if any, people have anticipated. Complex terrorism is particularly effective if its goal is not a specific strategic or political end, but simply the creation of widespread fear, panic, and economic disruption. This more general objective grants terrorists much more latitude in their choice of targets. More likely than not, the next major attack will come in a form as unexpected as we witnessed on September 11.

What should we do to lessen the risk of complex terrorism, beyond the conventional counter-terrorism strategies already being implemented by the United States and other nations? First, we must acknowledge our own limitations. Little can be done, for instance, about terrorists’ inexorably rising capacity for violence. This trend results from deep technological forces that can’t be stopped without producing major disruptions elsewhere in our economies and societies. However, we can take steps to reduce the vulnerabilities related to our complex economies and technologies. We can do so by loosening the couplings in our economic and technological networks, building into these networks various buffering capacities, introducing “circuit breakers” that interrupt dangerous feedbacks, and dispersing high-value assets so that they are less concentrated and thus less inviting targets.

These prescriptions will mean different things for different networks. In the energy sector, loosening coupling might mean greater use of decentralized, local energy production and alternative energy sources (like small-scale solar power) that make individual users more independent of the electricity grid. Similarly, in food production, loosening coupling could entail increased autonomy of local and regional food-production networks so that when one network is attacked the damage doesn’t cascade into others. In many industries, increasing buffering would involve moving away from just-in-time production processes. Firms would need to increase inventories of feedstocks and parts so production can continue even when the supply of these essential inputs is interrupted. Clearly this policy would reduce economic efficiency, but the extra security of more stable and resilient production networks could far outweigh this cost.

Circuit breakers would prove particularly useful in situations where crowd behavior and panic can get out of control. They have already been implemented on the New York Stock Exchange: Trading halts if the market plunges more than a certain percentage in a particular period of time. In the case of terrorism, one of the factors heightening public anxiety is the incessant barrage of sensational reporting and commentary by 24-hour news TV. As is true for the stock exchange, there might be a role for an independent, industry-based monitoring body here, a body that could intervene with broadcasters at critical moments, or at least provide vital counsel, to manage the flow and content of information. In an emergency, for instance, all broadcasters might present exactly the same information (vetted by the monitoring body and stated deliberately and calmly) so that competition among broadcasters doesn’t encourage sensationalized treatment. If the monitoring body were under the strict authority of the broadcasters themselves, the broadcasters would—collectively— retain complete control over the content of the message, and the procedure would not involve government encroachment on freedom of speech.

If terrorist attacks continue, economic forces alone will likely encourage the dispersal of high-value assets. Insurance costs could become unsupportable for businesses and industries located in vulnerable zones. In 20 to 30 years, we may be astonished at the folly of housing so much value in the exquisitely fragile buildings of the World Trade Center. Again, dispersal may entail substantial economic costs, because we’ll lose economies of scale and opportunities for synergy.

Yet we have to recognize that we face new circumstances. Past policies are inadequate. The advantage in this war has shifted toward terrorists. Our increased vulnerability—and our newfound recognition of that vulnerability—makes us more risk-averse, while terrorists have become more powerful and more tolerant of risk. (The September 11 attackers, for instance, had an extremely high tolerance for risk, because they were ready and willing to die.) As a result, terrorists have significant leverage to hurt us. Their capacity to exploit this leverage depends on their ability to understand the complex systems that we depend on so critically. Our capacity to defend ourselves depends on that same understanding.

Sidebar: Feeding Frenzies

Shorting out electrical grids or causing train derailments would be small-scale sabotage compared with terrorist attacks that intentionally exploit psychological vulnerabilities. One key vulnerability is our fear for our health—an attack that exploits this fear would foster widespread panic. Probably the easiest way to strike at the health of an industrialized nation is through its food-supply system.

Modern food-supply systems display many key features that a prospective terrorist would seek in a complex network and are thus highly vulnerable to attack. Such systems are tightly coupled, and they have many nodes—including huge factory farms and food-processing plants—with multiple connections to other nodes.

The recent foot-and-mouth disease crisis in the United Kingdom provided dramatic evidence of these characteristics. By the time veterinarians found the disease, it had already spread throughout Great Britain. As in the United States, the drive for economic efficiencies in the British farming sector has produced a highly integrated system in which foods move briskly from farm to table. It has also led to economic concentration, with a few immense abattoirs scattered across the land replacing the country’s many small slaughterhouses. Foot-and-mouth disease spread rapidly in large part because infected animals were shipped from farms to these distant abattoirs.

Given these characteristics, foot-and-mouth disease seems a useful vector for a terrorist attack. The virus is endemic in much of the world and thus easy to obtain. Terrorists could contaminate 20 or 30 large livestock farms or ranches across the United States, allowing the disease to spread through the network, as it did in Great Britain. Such an attack would probably bring the U.S. cattle, sheep, and pig industries to a halt in a matter of weeks, costing the economy tens of billions of dollars.

Despite the potential economic impact of such an attack, however, it wouldn’t have the huge psychological effect that terrorists value, because foot-and-mouth disease rarely affects humans. Far more dramatic would be the poisoning of our food supply. Here the possibilities are legion. For instance, grain storage and transportation networks in the United States are easily accessible; unprotected grain silos dot the countryside and railway cars filled with grain often sit for long periods on railway sidings. Attackers could break into these silos and grain cars to deposit small amounts of contaminants, which would then diffuse through the food system.

Polychlorinated biphenyls (PCB)—easily found in the oil in old electrical transformers—are a particularly potent group of contaminants, in part because they contain trace amounts of dioxins. These chemicals are both carcinogenic and neurotoxic; they also disrupt the human endocrine system. Children in particular are vulnerable. Imagine the public hysteria if, several weeks after grain silos and railway cars had been laced with PCBs and the poison had spread throughout the food network, terrorists publicly suggested that health authorities test food products for PCB contamination. (U.S. federal food inspectors might detect the PCBs on their own, but the inspection system is stretched very thin and contamination could easily be missed.) At that point, millions of people could have already eaten the products.

Such a contamination scenario is not in the realm of science fiction or conspiracy theories. In January 1999, 500 tons of animal feed in Belgium were accidentally contaminated with approximately 50 kilograms of PCBs from transformer oil. Some 10 million people in Belgium, the Netherlands, France, and Germany subsequently ate the contaminated food products. This single incident may in time cause up to 8,000 cases of cancer.

Further Reading

Many of the ideas introduced in this article are discussed further in Thomas Homer-Dixon’s The Ingenuity Gap: How Can We Solve the Problems of the Future? (New York: Alfred A. Knopf, 2000). See especially Chapter 4, which examines the nature and sources of complexity in our societies and technologies, as well as the discussion of the instabilities of complex technological systems and networks in Chapter 7 and of terrorism in Chapter 13.

A comprehensive technical treatment of complexity theory can be found in Dynamics of Complex Systems (Reading: Addison-Wesley, 1997) by Yaneer Bar-Yam. This book is not for the faint-hearted, and some knowledge of mathematics is helpful, but Bar-Yam is quite daring in his treatment of the social, political, and security implications of complexity. A truly groundbreaking discussion of the sources of complexity in biological, technological, and social systems is W. Brian Arthur’s “On the Evolution of Complexity” in Complexity: Metaphors, Models, and Reality, edited by G. Cowan, D. Pines, and D. Meltzer (Reading: Addison-Wesley, 1994). Countless writings examine the implications of rising complexity in our world, but four are particularly stimulating. The seminal discussion of the perils of complex technological systems is Charles Perrow’s Normal Accidents: Living With High-Risk Technologies (New York: Basic Books, 1984). Gene Rochlin examines the unexpected outcomes of the information revolution in Trapped in the Net: The Unanticipated Consequences of Computerization (Princeton: Princeton University Press, 1997). Langdon Winner’s wonderful article “Complexity and the Limits of Human Understanding” is rich with insights on the social and cognitive challenges posed by rising complexity. It can be found in a book that is worth reading in its entirety: Organized Social Complexity: Challenge to Politics and Policy (Princeton: Princeton University Press, 1975), edited by Todd La Porte. For a far more apocalyptic but tremendously provocative study of the risks of greater social complexity, see Joseph Tainter’s The Collapse of Complex Societies (Cambridge: Cambridge University Press, 1988).

On the vulnerabilities of modern infrastructure, see Critical Foundations: Protecting America’s Infrastructures (Washington: President’s Commission on Critical Infrastructure Protection, 1997) and Massoud Amin’s “National Infrastructures as Complex Interactive Networks” in Tariq Samad and John Weyrauch, eds., Automation, Control, and Complexity: An Integrated Approach (Chi-chester: John Wiley & Sons, 2000). For a journalistic account of how New York financial firms protected their critical infrastructure in the aftermath of the September 11 attacks, see Tom Foremski’s “How Business Could Survive” (Financial Times, October 10, 2001).

(Published Title: “We Ignore Misery at Our Peril”)

What we urgently need is subtlety of thought. We need to be able to make crucial distinctions, for instance between culpability and innocence, combatant and noncombatant, and the legitimate and illegitimate uses of force. If we make such distinctions, it’s more likely that we’ll guide ourselves successfully through this crisis. Sadly, though, subtlety is the first casualty of anger.

The debate surrounding the events of September 11 is being clouded by sloppy logic and analysis in the haste to say something — anything — that makes sense of the situation. One issue that has become clouded is whether it’s reasonable to talk about terrorism’s “root causes.” Some commentators declare that any discussion of root causes legitimizes terrorism by making excuses for it. Others suggest that people who want to examine root causes are arguing, essentially, that we shouldn’t take punitive action because it won’t work; we should act on the root causes instead.

But these are grade-school non-sequiturs. Let’s start with the first: Do we excuse or legitimize crime when we examine its causes? Of course not! And the same holds true for terrorism. We can explain why a person committed a crime — say, a murder — by pointing to the factors that caused the person to do it. We may even trace these factors far back into the person’s history — to their upbringing, their childhood economic circumstances and the like. But this rarely keeps us from holding the person morally responsible for the crime. We can, in other words, examine and acknowledge the root causes of the person’s behavior, without letting them off the moral hook. The two issues — of explanation and responsibility — are distinct.

One would think this is all pretty obvious. So why do some commentators object so vociferously to any discussion of terrorism’s root causes? I suspect it’s because they don’t like where this discussion may lead. They seem quite willing to accept some kinds of explanations of the latest barbarity — for instance, that the terrorists were depraved, mad, or the product of a particularly wicked sub-culture of radical Islam. Such explanations aren’t very threatening because they locate the cause in the nature of the perpetrators or their group. What really infuriates these commentators is any attempt to look at factors further afield — especially those that might lie in the structure and functioning of the planet’s economy, politics, and society. Why? Because such factors could implicate us in the West.

So, these commentators declare any consideration of root causes to be off limits. And they throw calumnies at anyone who raises these issues.

Yet by keeping us from learning about the origins of the threats we face, this attitude could easily make us less safe over the long run. Until we understand the sources of terrorism and do something about them, we can arm ourselves to the teeth, rampage across the planet with our militaries, suspend many of our civil liberties, and still not protect ourselves from this menace.

Now the second argument. Are those who want to examine the root causes of terrorism saying we should delay our efforts to track down and punish those responsible for this latest attack? Again, of course not.

The analogy of a terrible illness, like cancer, is useful here. We must excise the social pathology of terrorism – which means we must identify, track down, and destroy the culprits — just as we cut out a cancerous tumor. But when we’re dealing with a critical illness, the task usually doesn’t end there. We also want to change the underlying factors – such as smoking — that make cancer more likely to emerge in the first place.

What are terrorism’s underlying factors? They are many, they combine in complex ways, and they vary from one incident to another.

In the Middle East and South Asia, they include a demographic explosion that has produced a huge bulge of urbanized, unemployed young men — the most dangerous social group of all, according to many social scientists. They also include environmental stresses — especially shortages of cropland and fresh water – that have crippled farming in the countryside and forced immense numbers of people into squalid urban slums, where they are easy fodder for fanatics. The impact of these factors is compounded by chronic conflict (including the Israeli/Palestinian and Afghan conflicts) that have shattered economies and created vast refugee camps; by the region’s corrupt, incompetent, and undemocratic governments; and by an international political and economic system that’s more concerned about Realpolitik, oil supply, and the interests of global finance than about the well-being of the region’s human beings.

The receptivity of young men to terror’s radical message is enormously increased by this legacy of conflict, dislocation, and — yes — poverty in the region. From the refugee camps in Pakistan’s Northwest Frontier Province to the squalid streets of Gaza, we have ignored — for far too long — festering wounds of discontent.

At this point, though, many commentators stumble into yet another mistake: they say that such dislocation and poverty in distant lands can’t be among the root causes of terrorism, because the perpetrators of the New York atrocity apparently lived among us and were relatively educated and wealthy. But this argument assumes that people act only in response to their direct, personal experiences, which is absurd.

Sometimes terrorists are recruited directly from communities in misery. This seems to be the case with many of the Palestinian suicide bombers that plague Israel. Sometimes, though, they are recruited from wealthier and more educated groups — precisely because they can penetrate our societies more easily.

These people can still powerfully identify with communities elsewhere that they believe have been exploited, victimized, reduced to crushing poverty, or otherwise treated with disrespect. In fact, their relative wealth and education can reinforce a twisted sense of responsibility to do something for their suffering brothers and sisters. In the case of radical Islamic terrorists, such grievances are often expressed as anger over American policy toward Israel and Iraq and American support for “un-Islamic” Middle Eastern governments.

People who are miserable, or who strongly identify with those who are miserable, look for an explanation of that misery. Rightly or wrongly, they often focus their anger on those who are doing better. Inevitably, in a large group, some will be susceptible to wild and fantastic ideas that say violence is the solution.

As the disparities of wealth and opportunity on our planet widen, this problem is certain to get worse. We live in a seething, discontented world, and we ignore that fact at our peril.

Some events shatter the order of things — the routines and regularities of our lives that we rely upon for our sense of safety and our sense, most importantly, of who we are and where we are going. Some events change our perceptions forever. The world never looks the same again afterward. Suddenly, the reliable landmarks of life seem strange and distorted — recognizable, yet simultaneously weirdly unrecognizable.

It will take us a long time to unpack the full meaning of yesterday’s events, to develop a coherent understanding of what they mean for global society, for our nations, and for each of us as individuals. Yet three things are clear right now: first, the problem of international terrorism isn’t going to go away, in fact it’s almost certain to get worse; second, although a decisive, forceful response is necessary, force isn’t enough by itself — we must also act to address the roots of this madness; and, third, the worst thing we can do is overreact. Overreaction is exactly what the perpetrators want, and overreaction poses a grave threat to our democratic institutions.

The problem is going to get worse because of three trends, two technological and one social. New technologies are shifting power downward from large institutions and governments to small groups and individuals. Sometimes this is a good thing, as when the Internet empowers citizens to better participate in democratic processes.  But sometimes it’s a bad thing, because some groups are malign, and because one technology that’s diffusing downward is an extraordinary capacity to destroy.

Because of progress in materials engineering and miniaturization of electronics, explosives and the like, weapons are becoming cheaper, lighter, more rugged, more accurate, easier to use, and more powerful.  Meanwhile new communication technologies — from satellite phones to the Internet — allow terrorists and criminal syndicates to marshal their resources and coordinate their actions around the planet. As these trends continue, it’s easier for smaller and smaller numbers of people to hurt larger and larger numbers. Despite all the utopian hype, the new gadgets entering our lives are distinctly double-edged swords: We’ve unleashed technological forces that we don’t remotely understand and almost certainly can’t control.

Another trend is the growing complexity and interdependence of our technological systems, which makes it more likely that damage to one system component will ramify outwards to other components. We’ve seen such knock-on effects in the globe’s tightly wired financial system, when a crisis in a distant economy spreads like wildfire to others; we’ve even seen it in mundane infrastructure systems like electricity grids.

Terrorists can exploit this greater interdependence to magnify their disruptive power (that’s a key reason they went after the World Trade Center — at one blow, they may have killed a significant portion of the most skilled financial experts in United States). The first rule of modern terrorism, as one as astute analyst notes, should be to “find critical but nonredundant parts of the system and sabotage them according to your purposes.”

The third trend is social: the rapidly widening gulf between the planet’s richest and poorest groups, and between individuals and societies that thrive in the face of our world’s dramatic new challenges and those that fail and succumb. While the lives of people in even the world’s most impoverished corners have generally improved in recent decades, their progress has been snail-like compared to the stunning enrichment of the wealthiest.

Despite the miracles of modern communication and transportation, never in human history have the differences of wealth and opportunity among us been so great. These differences breed envy and frustration and, ultimately, anger. Thanks to the spread of TV, today’s disadvantaged know better than ever before what they are missing. And thanks to the spread of cheap, portable, and powerful technologies of violence, they also have a greater capacity than ever before to harm the targets of their anger.

If this is the future, how should we respond?

The natural reaction is to strike back — fast, furiously, and hard. Send in the cruise missiles and bombers; smash the bastards into the ground! But who, exactly? Even if the perpetrators of yesterday’s horror were state-backed (and it’s not clear they were), their links to specific governments will be evanescent threads, almost impossible to identify, easy to deny. Groups that do these things can now be so small, so dispersed, and so mobile that dealing with them is like trying to put your finger on quicksilver — crushing one cluster simply causes it to break into a thousand pieces and reform elsewhere.

We can’t afford to look weak at this critical moment. Some military response is essential. But a fast, unconsidered reaction will make us look weak, not strong. Our response has to be precise and carefully calibrated. This requires very good military intelligence, and one has to wonder if such intelligence is available, because the events yesterday were, more than anything else, a monumental intelligence failure — a failure, at least symbolically, on the scale of the failures that led to Pearl Harbor.

The very worst thing we can do is lash out at whoever seems to be nearby and plausibly connected with the horror. Because the “enemy” in this case is so diffuse and indeterminate, it would be easy to turn against groups and people within our societies — against anybody who looks different, who expresses opinions that vary from the norm, or who has been associated, at one time or another, with suspect people or causes.

We must guard against this impulse. It’s exactly what the terrorists want. They believe their appalling attacks will provoke us to reveal the true bigotry and violence of our societies that lurk behind the facade of democracy and tolerance.

Make no mistake. The unfolding terrorist threat in coming years will pose a profound test of our democratic institutions. Can we maintain the freedom of association that we’ve enjoyed in the past? The freedom of movement? The vigorous diversity of opinion? Will people who look a bit strange or different be singled out for random searches and interrogations? Can we resist the natural tendency to become more intolerant, suspicious, bitter, and militarized? Most importantly, can we remember that the problem will never go away if we don’t address the underlying disparities that help motivate such violence?

Some events shatter the order of things. The triumphalism that has permeated Western society in the last decade — the widely accepted conceit that Western capitalism, democracy, and science have brought us to the end of history — rings somewhat hollow now. History marches forward still, and a startling new chapter opened yesterday.