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
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.257
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
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
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.258 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.259
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.261 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.262 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
