The World in 2050_ Four Forces Shaping Civilization's Northern Future - Laurence C. Smith [47]
To the north and south, straddling the lush equatorial belt and monsoonal areas like the dried-out bun halves of a veggie sandwich, are two huge drought-stricken bands of drylands and deserts. The Sahara, Arabian, Australian, Kalahari, and Sonoran are all found here, huddled at roughly 30º N and S latitude. While not lifeless, these zones are decidedly stark compared with their green equatorial neighbor. They mark the killing fields of the moist ITCZ air masses. Emptied of their rain holdings, the air masses drift north or south before tumbling earthward again, baking the land with crushing dry heat, pressed downward by the weight of still more air falling from above. Like the perpetual circuit of rising and falling wax in a Lava lamp, this sinking air closes the convection loop, flowing from both hemispheres back toward the equator in the form of trade winds. From there, the Sun’s rays will moisten and lift the air once again, repeating the cycle. This overall pattern of atmospheric circulation, called the Hadley Cell, is one of the most powerful shapers of climate and ecosystems on Earth.
Despite the harsh aridity, billions of people live in or around those twin subtropical blast zones of sinking dry air, which contain some of our fastest-growing human populations. Pressing hard into the Sahara’s southern flank are nearly eighty million people of Africa’s Sahel, a population projected to reach two hundred million by 2050.201 North of the Sahara are the large populations of northern Africa and Mediterranean Europe. Australian cities cling to the coastline of their dusty continent, leaving the continent’s vast desert interior mostly uninhabited. But the parched Middle East, southern Africa, and western Pakistan are heavily populated and have some of the youngest, fastest-growing populations in the world.
Phoenix and Las Vegas—two briskly growing cities in the arid southwestern United States—lie in the middle of a Hadley Cell desert. Nineteen million people can survive in Southern California only because there are a thousand miles of pipelines, tunnels, and canals bringing water to them from someplace else. It comes from the Sacramento-San Joaquin Delta and Owens Valley to the north, and from the Colorado River to the east, far across the Mojave Desert. They enjoy green lawns, burbling fountains, and swimming pools in a place where rainfall averages less than fifteen inches per year. A second canal202 from the Colorado pumps water up nearly three thousand feet in elevation and 330 miles east to Phoenix and Tucson, prompting Robert Glennon, author of Water Follies, to observe that we literally move water “uphill to wealth and power.”203 Without this infrastructure and the energy to run it, Arizonans’ water supply would more closely resemble that of Palestinians: fifteen dubious gallons a day haggled from the back of a water trafficker’s truck.
Which Is Worse?
Even if there were no climate change, the world would still be facing declining per capita water supply because of our growing economy and population. In general, more people means more water demand. Even if we could freeze population growth, advancing modernization means more meat, finished goods, and energy, all of which raise per capita water consumption.204 Contrary to common perception, population growth and industrialization thus represent an even bigger challenge to the global water supply than does climate change.
Policy wonks and water managers have long sensed this. But hydrologist Charlie Vörösmarty blew it wide