雅思阅读材料：A Drier and Hotter Future

　　Tim Barnett and David Pierce of the Scripps Institution of Oceanography estimate that to adjust to a sustainable level of supply, consumers of Colorado River water will have to get along with 20 percent less water than they use today. That is still a lot of water to lose, but the loss may not be catastrophic. Urban users are already conserving about as much as they can per capita. Farmers, on the other hand, who consume about 80 percent of the western water supply, including in California, are wasting much through inefficient management and low-value crops. Half of the water goes to raise alfalfa to feed cattle, and much of the rest evaporates or soaks into the sand. If some of agriculture’s share could be diverted to cities, there might be enough to sustain the current population. Rural communities would decline, some lucky farmers would retire with a potful of money, and the public would have to figure out where to get its lettuce, tomatoes, oranges and meat. The cost of water would go up dramatically, and those without money would go thirsty and leave. New hierarchies would take the place of old ones.

　　Thirty million people now depend on the Colorado River. Perhaps they can manage to adjust to a diminished flow and to declines in domestic food supplies and hydroelectric power. But more people are on the way: Demographers calculate that the population of the Southwest may increase by 10 or 20 million between now and 2050. Some of those people will come from other parts of the country, some from Mexico and Central America, and some from other nations that are coping poorly with their current problems or are overwhelmed by climate change. Whatever their origin, the new arrivals will go to the familiar oases, hoping to find the good life with a swimming pool and a green lawn.

　　Developers are eager to make money by selling homes to these newcomers. The political and economic culture of the Southwest is dead set against any acknowledgment of limits to growth. In the last few chapters of the book, deBuys shows that even now those in power refuse to accept any check to expansion; business must be free to do business. Others say that they are helpless to stop the influx: Patricia Mulroy, general manager of the Southern Nevada Water Authority in Las Vegas, declares, "You can’t take a community as thriving as this one and put a stop sign out there. The train will run right over you." Her solution is to create an expensive "straw" to extract water from a shrinking Lake Mead, drawing on the "dead pool" that will be left below the intakes for generating electricity. She doesn’t have the money to build that straw right now, but she is working hard to keep her improbable city from drying up and becoming a casualty like ancient Mesopotamia. Similarly, Phoenix continues to issue building permits helter-skelter and counts on "augmenting the supply" of water sometime in the future. But where will the state and city go for more supply, and how will they bring it cheaply over mountains and plains to keep Phoenix sprawling into the sunset?

　　DeBuys gathers enough scientific evidence to make a convincing case against that growth mentality. A similar case could be made against growth in the rest of the United States, although in the East the threat may be too much water, not too little, and too many storms, not too much smoke and dust. The past warns us that ancient peoples once failed to adapt and survive. Will theirs be America’s fate? Perhaps. But past human behavior may not be a reliable indicator of how people will behave in the future. If the environment is becoming nonlinear and uNPRedictable, as deBuys argues, then human cultures may also become nonlinear and uNPRedictable. No other people have had as much scientific knowledge to illuminate their condition. What we will do with that knowledge is the biggest imponderable of all.