of the global atmospheric circulation itself.
Rainmaker, Land Baker
Just a hundred steps into the rain forest my head was thudding, my shirt drenched, and I couldn’t breathe. It wasn’t claustrophobia—although I couldn’t see well through the green gloom of filtered canopy light—but the wet, steaming heat. It was like inhaling vapors over a teakettle. Something went soft under my foot—I had unwittingly crushed an exotic caterpillar the length of my hand. I excused myself from the group and walked gasping back toward the boat, but was intercepted by an aboriginal man. He was selling tiny clay couples with enormous genitalia, eternally frozen in joyous copulation. Back on the boat, a hot breeze blew down the Amazon River but my skin dripped even faster. The air was totally saturated. I couldn’t wait to get back to my air-conditioned hotel room in Manaus.
I must have caught the Amazon on a bad day. Most living things love tropical rain forests. Their wide green sash—plain on any world map, roughly encircling the equator—is bursting with life and contains the vast majority of species, known and as yet undiscovered, on Earth. Rain forests grow there thanks to the condensate downpours dumped by the moist, rising air masses of the Intertropical Convergence Zone (ITCZ). This band of clouds and rain follows the Sun, circling nearly directly overhead, as it sizzles the equatorial oceans and landmasses to evaporate huge quantities of water vapor. The vapor rises, cools, and condenses, deluging the tropics with rain and triggering the Asian and African monsoons as the ITCZ drifts back and forth across the equator each year, endlessly chasing the seasonal march of the Sun. Billions of living things hang on the strength and reliability of these annual rainfall patterns, including us.
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 30? 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
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 Vorosmarty blew it wide open in 2000 when he and his colleagues Pamela Green, Joe Salisbury, and Richard Lammers at the University of New Hampshire compared climate and hydrologic models with long-term population and water-consumption trends.205 As part of the study, they published three brightly colored maps of projected water demand for 2025. I make my students stare at these maps at least once in my introductory course lectures at UCLA.
One of the maps is quite scary-looking and captures the combined effects of both climate and population trends on human water-supply stress. Most of the world is colored red (indicating less water availability than today) with a few places colored blue (more water availability, mostly in Russia and Canada) and even fewer in green (meaning little or no change). This fearsome red map suggests that by the year 2025 much of humanity’s water supply will be worse off, either from population growth, or climate change, or both.
The other two maps separate out the effects of population and climate change. The population-only map is even scarier than the combined map. Nearly all the world is bathed in red, with blue colors even rarer than before. Compared to it, the climate-only map seems almost benign, with roughly equal proportions of blue and red tones and even more in green. In other words, climate changes are expected to both harm and help water availability in different parts of the world, whereas population and economic growth harm it nearly everywhere.206 So even if our climate-change problems could somehow disappear tomorrow (and they won’t), we would still face enormous challenges to water supply in some of the hottest, most crowded places on Earth.
Drinking Sh**
It’s hard to imagine the world behind those red maps. To most people—especially living in cities—clean water is like oil and electricity: one of those things upon which they depend mightily yet give barely a passing thought. In my own city of Los Angeles, everyone will gladly pay a hundred dollars a month for cable television, yet would roar in protest if forced to pay that much for life’s elixir piped directly into their homes. When Governor Schwarzenegger declared a state of drought emergency, I studied my water bill closely for the first time in my life. For two months of clean drinking water, snared from faraway sources and delivered to my house by one of the world’s most expensive and elaborate engineering schemes, I was charged $20.67. I spend more on postage stamps.
If only everyone could indulge such ignorant bliss. While eight in ten people have access to some sort of improved water source,207 this globally averaged number masks some wild geographic discrepancies. Some countries, like Canada, Japan, and Estonia, provide clean water to all of their citizens. Others, especially in Africa, do so for under half. The worst water poverty is suffered by Ethiopians, Somalis, Afghanis, Papua New Guineans, Cambodians, Chadians, Equatorial Guineans, and Mozambicans.208 Even their statistics hide the most glaring divide—between cities and rural areas. Eight in ten urban Ethiopians have some
