The World in 2050: Four Forces Shaping Civilization's Northern Future (16 page)

The Great Twenty-first-Century Drought?

Part of the explanation for the many floods and droughts that happened around the world in 2008 was that it was a La Niña year, meaning that sea surface temperatures (SSTs) in the eastern half of the tropical Pacific Ocean cooled off. This triggered, among other things, dry conditions over California, contributing to its ongoing drought (her counterpart, El Niño, is associated with warm SSTs and wetter conditions there). Through connections between the sloshing ocean and the atmosphere, this “Little Girl” had impacts on human water supply that reverberated worldwide.

My UCLA colleague Glen MacDonald, an expert in the study of prehistoric climate change, is deeply concerned that something like the 2008 La Niña could happen again—but persisting for
decades
rather than months. In fact, MacDonald and his students believe the American Southwest, in particular, could be struck by a drought worse than anything ever seen in modern times. From shrunken tree-rings and other prehistoric natural archives, they have assembled a growing body of evidence that the region suffered at least two extended “Perfect Droughts” (coined by MacDonald to describe periods when Southern California, northern California, and the upper Colorado River Basin all experienced drought simultaneously) during medieval times.
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These Perfect Droughts were as bad as or worse than the Dust Bowl but lasted much longer, persisting as long as five to seven decades (the Dust Bowl lasted barely one). These prehistoric data tell us that this heavily populated region is capable of experiencing droughts far worse than anything experienced since the first European explorers arrived.

One reason for these massive prehistoric droughts was that between seven hundred and nine hundred years ago temperatures rose. The increase was similar to what we are beginning to see now but not so high as what climate models are projecting by 2050. The reason for the medieval temperature rise (fewer volcanic eruptions plus higher solar brightness) was different from what’s happening today, but it nonetheless provides us with a glimpse of how our planet might respond to greenhouse warming.
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Not only did the medieval climate warming increase the drying of soils directly, it may also have altered an important circulation pattern in the Pacific Ocean, by shifting relatively cool water masses off the western coast of North America for many decades at a time (this would be a prolonged negative phase of the so-called “Pacific Decadal Oscillation,” an El Niño- like oscillation in the northern Pacific that currently vacillates over a 20-30-year time scale). This likely created pressure systems driving rain-bearing storm tracks north, rather than south, across the western United States, triggering drought conditions in the American Southwest. Should the projected rise in air temperatures cause the Pacific circulation to behave like this again, the prolonged medieval megadroughts could return. Similar connections between shifting sea-surface temperatures and geographic rainfall patterns over land exist for the Atlantic and Indian oceans as well.

MacDonald points out that by the time Schwarzenegger declared a state of emergency in 2009, most of the southwestern United States was actually in its eighth year of drought, not third. “Arguably, we are now into the great Twenty-first Century Drought in western North America,” he mused to me. “Could we be in transition to a new climate state? Absolutely. Should we be worried? Absolutely.” His concerns are echoed by Richard Seager at Columbia University’s Lamont-Doherty Earth Observatory. In a widely read
Science
article,
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Seager and his colleagues showed consensus among sixteen climate models that projected greenhouse warming will drive the American Southwest toward a serious and sustained baking. Their result, of course, is dependent on the group of models analyzed, and the simulation is imperfect because today’s coarse-scale climate models don’t represent mountainous areas very well (e.g., the Rockies, which produce most of the region’s snowpack water). But if these model projections prove correct, then the drought conditions associated with the brief American Dust Bowl could conceivably become the region’s new climate within years to decades.

Risky Business

“Stationarity Is Dead,” announced another
Science
article in 2008, sending a cold shiver through the hearts of actuaries around the world.
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A hydrology dream team of Chris Milly, Bob Hirsch, Dennis Lettenmaier, Julio Betancourt, and others had just told them that the most fundamental assumption of their job description—reliable statistics—was starting to come apart.

Stationarity—the notion that natural phenomena fluctuate within a fixed envelope of uncertainty—is a bedrock principle of risk assessment. Stationarity makes the insurance industry work. It informs the engineering of our bridges, skyscrapers, and other critical infrastructure. It guides the planning and building codes in places prone to fires, flooding, hurricanes, and earthquakes.

Take river floods, for example. By continuously measuring water levels in a river for, say, twenty years, we can then use the stationarity assumption to calculate the statistical probability of rarer events, e.g., the “fifty-year flood,” “hundred-year flood,” “five-hundred-year flood,” and so on. This practice, while creating enormous misunderstanding with the public,
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has also made us safer. Hard statistics, rather than the whims of developers or mayors, are used to design bridges and for zoning. But flood prediction, and most other forms of natural-hazard risk assessment, rest on the core assumption that the statistics of past behavior will also apply in the future. That’s stationarity. Without it, all those risk calculations go straight out the window.

A growing body of research is showing that our old statistics are starting to break down. Climate change is not the sole culprit. Urbanization, changing agricultural practices, and quasi-regular climate oscillations like El Niño all influence the statistical probabilities of flooding. However, the dream team’s paper and others like it
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tell us that climate change is fundamentally altering the statistics of extreme floods and droughts, two things of enormous importance to humans. “In view of the magnitude and ubiquity of the hydroclimatic change apparently now under way,” they wrote, “we assert that stationarity is dead and should no longer serve as a central, default assumption in water-resource risk assessment and planning. Finding a suitable successor is crucial for human adaptation to changing climate.”
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Unfortunately, we have no good replacement for stationary statistics yet, certainly nothing that works as well as they once did. Moreover, there has been hardly any basic research done in this area since the 1970s. We can’t just invent a completely new branch of mathematics and train a new generation of water experts in it overnight. “Water resources research has been allowed to slide into oblivion over the past thirty years,” Lettenmaier growled later in a separate editorial. “Certainly the profession has been slow to acknowledge these changes and acknowledge that fundamentally new approaches will be required to address them.”
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So even as we’re beginning to grasp the enormity of this problem, we presently have no clear replacement for our old way of doing things. Until we find one, risks will be harder to predict and to price. We can expect insurance companies to react accordingly. In 2010, after failing to win a nearly 50% rate increase from state regulators, Florida’s largest insurance company abruptly canceled 125,000 homeowner policies in the state’s hurricane-prone coastal regions, saying the recent series of devastating hurricanes had rendered its business model unworkable.
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Get ready for higher premiums, uninsurable properties, and failed or overbuilt bridges.

Nonreturnable Containers

Changing drought and flood statistics are not the only way that rising greenhouse gases harm our water supply. All of our reservoirs, holding tanks, ponds, and other storage containers are trifling compared to the capacity of snowpacks and glaciers. These are free-of-charge water storehouses, and humanity depends upon them mightily.

Snow and ice hoard huge amounts of freshwater on land, then release it in perfect time for the growing season. They do this by bulking up in winter, then melting back in spring and summer. They are the world’s hugest water-management system and, unlike a dam reservoir, displace no one and cost nothing. Glaciers (and permanent, year-round snowpacks) are especially valuable because they outlast the summer. This means they can hoard extra water in cool, wet summers, but give it back in hot, dry summers, by melting deeply into previous years’ accumulations. Put simply, glaciers sock away water in good years when farmers need it least, and release water in bad years when farmers need it most. Glaciologists call these “positive mass-balance” and “negative mass-balance” years, respectively, and they are a gift to humanity. Glaciers keep the rivers full when all else is dry. They are the ultimate sunny-day fund.

If you read the news, then you already know that many of the world’s glaciers are beating a hasty retreat, whether through warmer temperatures, less precipitation, or both. Ohio State University’s glaciologist power-couple Lonnie Thompson and Ellen Mosley-Thompson have been photographing the deaths of their various study glaciers since the 1970s. Some of these are even wasting away at their summits, which is a death knell for a glacier. There are ski resorts in the Alps trying to save theirs by covering them with reflective blankets. Most glaciologists expect that by 2030, Montana’s Glacier National Park will have no glaciers left at all.

Seasonal snowpack, which does not survive the summer, cannot carry forward water storage from year to year like glaciers do, but it is also a critically important storage container. It creates a badly needed time-delay, releasing water when farmers need it the most. By holding back winter precipitation in the form of snow, the retained water flows downstream to farmers later, in the heat of the growing season. Without this huge, free storage container, this water would run off uselessly to the ocean in winter, long before growing season. Rising air temperatures harm this benefit, both by increasing the prevalence of winter rain (which is not retained) and by shifting the melt season to earlier in the spring. Because the growing season is determined not only by temperature but also the length of daylight, farmers are not necessarily able to adapt by planting sooner. By late summer, when the water is needed most, the snowpack is long gone.

This seasonal shift to earlier snowmelt runoff portends big problems for the North American West and other places that rely on winter snowpack to sustain agriculture through long, dry summers. California’s Central Valley—the biggest agricultural producer in the United States—depends heavily on Sierra snowmelt, for example. But the long-term projection for health of the western U.S. snowpack is not good. It has already diminished in spring, despite overall
increases
in winter precipitation, in many places.
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By late 2008, Tim Barnett at the Scripps Institute of Oceanography and eleven other scientists had definitively linked this phenomenon to human-caused climate warming. This is not good news, they wrote in
Science,
warning of “a coming crisis in water supply for the western United States” and “water shortages, lack of storage capability to meet seasonally changing river flow, transfers of water from agriculture to urban uses, and other critical impacts.”
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High-profile research like this does not go unnoticed by policy makers. One response is to build more reservoirs, canals, and other engineering schemes to store and move water. China is now planning fifty-nine new reservoirs in its western Xinjiang province to retain water from glacier-fed rivers. In 2009, U.S. Interior Secretary Ken Salazar announced $1 billion in new water projects across the American West, with over a quarter-billion going to California alone.
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Thus begins our new technological race—to adapt to a shrinking water storage capacity, once provided for free by snow and ice. But it is important to understand that
no amount of engineering can replace that storage
. Think back to I. A. Shiklomanov (p. 86), his huge container of ice, and trifling container of surface water. Even if we quadrupled the world’s reservoirs, they wouldn’t come remotely close to replacement. And even if they did, we’d still end up with less water: Unlike snow and ice, water evaporates like crazy from open reservoirs.

We can’t hold it all back. More of the world’s water is leaving the mountains to run to the sea.

Into the Sea

It’s abnormal to be thinking about melting glaciers when standing on a nice sunny beach during holiday break. But this was no ordinary beach and no ordinary holiday. It was Christmas 2005, and I and other members of the Smith family were staring dumbly at the bones of what had once been my aunt and uncle’s house, a dozen blocks inland from the Mississippi coast. With the ease of a kid blowing foam across a cup of hot chocolate, Hurricane Katrina had thrown a wall of water—a
storm surge
—right through their lovely Biloxi neighborhood.

The place was a deserted war zone. Houses smashed to splinters, cars crushed and tossed into swimming pools. Nearer the beach, there were no house bones at all, just smooth rectangles of white concrete, scrubbed and gleaming to show where million-dollar homes had once stood. It was four months since the hurricane but the place was abandoned. No one was hauling away debris, no sound of hammering nails. All was silent except for the songbirds, cheeping and squabbling amid the wreckage. To them it was just another beautiful day on the American Gulf Coast.

In devastated New Orleans, ninety miles to the west, we saw a similar abandonment of entire neighborhoods. There were blocks and blocks of leaning houses, trashed and dark except for the colorful graffiti of rescue-worker symbols. The hieroglyphs recorded each house’s history in spray paint—the date searched, any noted hazards, whether any human bodies had been found. Living in one home was a pack of feral dogs.

So that is why, while standing on a gorgeous sunny beach, I was thinking about glaciers. In smashing my uncle’s former home, Hurricane Katrina had made the dry statistics of my field feel real—on a personal, visceral level. Although glacial melt hadn’t caused Katrina, I was thinking about the indelible control the world’s ice holds over our coastlines. When the glaciers grow, oceans fall. When they shrink, oceans rise. Oceans and ice have danced in this way, embraced in lockstep, for hundreds of millions of years. From my geophysical training I knew this. From my own research and that of colleagues, I knew how quickly the world’s glaciers were retreating. And for miles inland behind me, and hundreds of miles along the coast in either direction, the ground on which I stood lay barely above the surf. I had understood all this before in abstraction, but this endless plain of destruction made it real.

Global sea levels are now steadily rising nearly one-third of a centimeter every year, driven by melting glacier ice and the thermal expansion of ocean water as it warms.
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There is absolutely no doubt about this. There is absolutely no doubt that it will continue rising for at least several centuries, and probably longer. Sea-level rise really is happening. The big unknowns are how fast, whether it will progress smoothly or in jerks, and how high the water will ultimately go.

We shall explore the scary possibilities of fast sea-level rise in Chapter 9; for now, let’s stick to conservative models and what has been measured thus far. In the 1940s, global average sea level was about ten centimeters lower than today, but was rising more than 1 millimeter per year (a brisk rate at the time). It is currently rising 2-3 millimeters per year, and that number is projected to grow by around 0.35 millimeters for each additional degree Celsius of climate warming.
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Depending on whose model you like, this means we are looking at around 0.2-0.4 meters of sea level rise by 2050, or calf-deep. The state of California has just begun damage assessment and planning for 0.5 meters by that time,
^259
,
260
around knee-deep. And 2050 is just the beginning. By century’s end, global sea level could potentially rise from 0.8 to 2.0 meters.
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That’s a lot of water—up to the head of an average adult. Much of Miami would be either behind tall dikes or abandoned. Coastlines from the Gulf Coast to Massachusetts would migrate inland. Roughly a quarter of the entire country of Bangladesh would be underwater.

When oceans rise, all coastal settlements face challenges. Higher sea levels expand the inland reach and statistical probability of storm surges like the one Hurricane Katrina blew into the Gulf Coast. Decidedly unhelpful is a two-in-three chance that climate warming will make typhoons and hurricanes more intense than today, with higher wind speeds and heavier downpours.
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And just as we saw for water supply, there are other, nonclimatic actors that make the problem even worse. In fact, all four of our global forces are conspiring to place some of the world’s most important cities at risk.

Most of the world’s largest and fastest-growing urban agglomerations—like Mumbai, Shanghai, and Los Angeles—are globalized port cities on the coasts. Their populations and economies are rising fast. Demographers and economic models tell us they will grow even more over the next forty years.

Particularly in Asia, many of these great cities are located on “megadeltas,” enormous flat protrusions of mud and silt that grow where large rivers drop off their carried sediment upon entering and dissipating into the ocean. These piles of sediment are ferociously attacked by the ocean’s waves and storm surges, but the rivers keep dumping more. Like giant conveyer belts of cement, they keep trundling material to the river mouths—often from thousands of miles inland—to overwhelm the ocean’s defenses. Over centuries to millennia, the rivers grow the land out.

These deltas have always attracted humans. Farmers love their thick, rich soils that are also flat, well-watered, and have few rocks. Ships can ply both oceans and continental interiors. The river brings in freshwater for towns and cities, then carries their wastes off to the sea. A delta’s flat terrain is appealing to build on; the surrounding swamps and forests are teeming with fish and wildlife.

The problem, of course, is that the very existence of deltas is maintained by the constant sedimentation from flooding and back-and-forth migration of their rivers. They are full of low-lying swales that inundate readily. As human settlements grow, there is increasing pressure to expand into these dangerous areas. This happens not only with deltas but urbanizing river floodplains as well, like Cedar Rapids in Iowa. Flood damages therefore rise as development pushes into low-lying swamps considered too dangerous before. The reason Katrina spared New Orleans’ historic French Quarter is that it was the first place to be colonized: Even in 1718 people knew to perch their houses on that crescent-shaped sliver of natural levee, piled a few feet higher than the nearby swamps where the Upper Ninth Ward would drown nearly two centuries later.

As delta cities grow and their rivers become oversubscribed or polluted, they start pumping their groundwater resources. Groundwater removal—from what is essentially a pile of wet mud—causes the delta sediments to compact and settle, lowering the delta’s elevation closer to that of the sea. Even in the absence of groundwater pumping, some settling is normal. In a natural system, this settling is compensated by fresh blankets of silt laid down by floods. But the dikes and levees built to protect delta cities also prevent these fresh reinforcements from arriving. Farther upstream, dams thrown across the river snare the delta’s lifeblood of new sediment. Dam operators groan and search their budgets for dredging money. The conveyor belt is cut. Hundreds of miles downstream, the ocean starts taking back the land.

Important delta cities are found all over the world. They face the triple threat of rising oceans, sinking land, and sediment-starved coastlines. Without replenishment their coasts are washing away, bringing ocean wave energy and storm surges ever closer to the sinking cities. When combined with projected trends of rising sea level, population, and economic power, this puts some of the world’s most populous and prosperous places in harm’s way.

The risk assessment study on the next page was recently commissioned by the OECD.
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The study considered all 136 of the world’s major port cities holding one million people or more. As of 2005, about forty million people living in these cities were considered to be living in places at direct risk from flooding. The total economic exposure to flooding—in the form of buildings, utilities, transportation infrastructure, and other long-lived assets—was about USD $3 trillion, or 5% of global GDP.
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Under current trajectories of population growth, economic growth, groundwater extraction, and climate change, by the 2070s the total exposed population is forecast to grow more than threefold, to 150 million people. The economic exposure is forecast to rise more than tenfold, to USD $35 trillion, or 9% of global GDP. Of the top twenty major at-risk cities, exposed human populations could rise 1.2- to 13-fold, and exposed economic assets 4- to 65-fold, by the 2070s. Three-quarters of these major cities—nearly all of them in Asia—are found on deltas. Clearly, we are about to begin paying great attention to a new kind of defense spending. It’s called coastal defense.

Top Twenty World Port Cities Most Vulnerable to global Sea Level Rise, Hurricanes, and Land Subsidence

(
Sources:
R.J. Nicholls, OECD, 2008)