But what if, in fact, the old war stories are becoming obsolete? The engineer, like the insurance agent, is hampered by the fact that his skill depends on the earth behaving in the future as it has in the past. As Petroski writes,
Since it is future failure that is at issue, the only sure way to test our hypotheses about its nature and magnitude is to look backward at failures that have occurred historically. Indeed, we predict that the probability of occurrence for a certain event, such as a hundred-year storm, is such and such a percentage, because all other things being equal, that has been the actual experience contained in the historical meteorological record.
That record, however, is now shattered. In the course of Petroski’s lifetime, and all of ours, we’ve left behind the Holocene, the ten-thousand-year period of benign climatic stability that marked the rise of human civilization. We’ve raised the global temperature about a degree so far, but a better way of thinking about it is: we’ve amped up the amount of energy trapped in our narrow envelope of atmosphere, and hence every process that feeds off that energy is now accelerating. For instance, this piece of simple physics: warm air holds more water vapor than cold. Already we’ve increased moisture in the atmosphere by about 4 percent on average, thus increasing the danger both of drought, because heat is evaporating more surface water, and of flood, because evaporated water must eventually come down as rain. And those loaded dice are doing great damage. The federal government spent more money last year repairing the damage from extreme weather than it did on education.
Engineers try to cope with these changes, of course, especially those on the front lines. So, for instance, public works departments across the Northeast have begun replacing the pipe-like drains called culverts as fast as they can, swapping the size that the textbooks recommend for the much larger diameters the new rainfalls demand. “The books we’ve always used to design culverts, you can throw them all out,” Dave Wick, district manager of the Warren County Soil and Water Conservation District, recently said. “What was once called a 100-year event is now a 50-year event, and a 50-year event has become a 25-year event.” And indeed even those numbers may be optimistic—James Hansen, who retired earlier this spring from NASA, calculated recently that, as a summary put it, events like
the recent Texas heat wave, Moscow’s heat wave the year before, and the 2003 heat wave in Europe now occur twenty-five to fifty times more often than just fifty years ago.
The first problem for engineers, of course, is that the changes you need to make to deal with these shifts—bigger culverts, different pavement that won’t buckle in the heat, more water storage behind higher dams—all lead to more expense. The Crown Point Bridge, for instance, was lost due to engineering failure after eighty years; now a new one stands in its place, presumably good for a similar term. No one can really complain. But Vermont lost many more bridges in 2011, some of them covered bridges that had taken everything nature threw at them for centuries, only to be swept away in the record rainfalls that accompanied Hurricane Irene.
As they’re replaced, prudence demands that they be built much longer than their predecessors, so that a similar flood won’t wash away the banks that hold them—in fact, a state report on the flooding specified exactly that measure. But a longer bridge is a more expensive one and, as Petroski points out, length adds stress that will lead to more deterioration unless a span is carefully maintained. (And, of course, it makes it harder to rebuild the covered bridges that are highly useful to state tourism officials.) Hurricane Sandy, a year after Irene, demonstrated far more fundamental weaknesses in our technological civilization—a subway system, say, is an engineering marvel right up to the moment when it fills with seawater.
A deeper problem, however, is that there’s no new normal to aim for, no way to reestablish the textbook formulas that served us well. We’ve increased the temperature one degree so far, but the same climatologists who predicted that rise also tell us that unless we can quickly break our addiction to fossil fuels, we can anticipate four or five degrees as the century wears on. Each increment adds new energy to the system, and at the upper boundaries engineering as we’ve known it becomes very nearly impossible. If the atmosphere is 8 percent wetter instead of 4 percent, what kind of bridges do we build? Where do we put roads so they’re not washed away? What, if anything, should we be building in those zones (like, say, Manhattan) that are only a few meters above a rising sea? If the danger of forest fire grows constantly, what kind of building codes do we need for construction in the West?
These are problems not just for the engineer, but for his constant companions, the bond salesman and the insurer. Each of these has to assure himself that new projects are within some new margin of safety so that their investments and estimates of risk make economic sense; if they don’t, the cost of building bridges will reach the level where we go straight back to ferries.
If the engineering goals of the past were to build longer bridges and higher skyscrapers and cheaper, more graceful structures generally, are those still sensible goals? Or in a more difficult world, might we choose a different set of targets, and in the process change many professions, engineering included? You could argue, I think, that a less hospitable earth might, in many places, dictate a design style geared toward the squat, the durable, the hardy. Instead of a few big, inherently vulnerable structures (giant power plants, say, that could be taken out by a flood or a storm), engineers are increasingly interested in “distributed generation,” the idea of a thousand or a million rooftops covered with solar panels and each feeding into a grid. Such new arguments present engineering challenges of their own—how do you store the power when the sun doesn’t shine, or redirect it from sunny places to dark ones? But it’s clearly less vulnerable to catastrophic failure.
In fact, most of what Petroski describes are all-or-nothing failures. The bridge works, or it falls. But in a tougher world we’ll need more structures and systems that can fail gradually, where problems don’t immediately ramify into catastrophes. If a flooding river washes away my house and with it my solar panels, I’ll be miserable, but the whole East Coast doesn’t go black. By Petroski’s standards such a loss would be an obvious failure. But by the standards of a far more turbulent and difficult world, it may also be a kind of success. The Army Corps of Engineers worked the better part of a century to make sure the lower Mississippi never flooded, but when record volumes of water came down the river in the spring of 2012, they were able to blow up some levees and inundate farmland, sparing cities. That was an engineering accomplishment as much as a setback.
This kind of thinking extends beyond threats to physical objects, of course. Twice Petroski mentions in passing the current financial crisis, but in neither case, oddly, does he bring up the phrase that became emblematic of the saga: “too big to fail.” In political terms, that apparently meant “we must bail them out.” But to any thinking person watching from the sidelines, there was another obvious implication. Anything too big to fail was too big. Period. The remedy was to make it smaller—a thousand small banks, not six big ones.2 So far those big banks have used their political clout to resist such rearrangement, just as the big energy companies have fought small energy sources. But if Petroski’s account proves anything, it’s that the forces of the real world may eventually prevail on even the mightiest structures.
2 This is not an entirely radical notion—in late March 2012, for instance, the research department of the Dallas Federal Reserve made front-page news when it called for breaking up those concentrated centers of financial power: “Downsizing the behemoths over time into institutions that can be prudently managed and regulated across borders is the only appropriate policy response.” See Christopher Matthews, “President Calls for The End of ‘Too Big To Fail,’” Time.com, March 22, 2012. ↩
This is not an entirely radical notion—in late March 2012, for instance, the research department of the Dallas Federal Reserve made front-page news when it called for breaking up those concentrated centers of financial power: “Downsizing the behemoths over time into institutions that can be prudently managed and regulated across borders is the only appropriate policy response.” See Christopher Matthews, “President Calls for The End of ‘Too Big To Fail,’” Time.com, March 22, 2012. ↩