The World in 2050_ Four Forces Shaping Civilization's Northern Future - Laurence C. Smith [61]
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