For Want of a Drink
1. When the word water appears in print nowadays, crisis is rarely far behind. Water, it word居中is said, is the new oil: a resource long squandered, now growing expensive and soon to be overwhelmed by insatiable demand. Aquifers are falling, glaciers vanishing, rervoirs drying up and rivers no longer flowing to the a. Climate change threatens to make the problem wor. Everyone must u less water if famine, pestilence and mass migration are not to sweep the globe.
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2.The language is often overblown, and the remedies sometimes ill-conceived, but the basic message is not wrong. Water is indeed scarce in many places, and will grow scarcer. Bringing supply and demand into equilibrium will be painful, and political disputes may increa in number and intensify in their capacity to cau trouble. To carry on with prent practice would indeed be to invite disaster.
3.Why? The difficulties start with the sheer number of people using the stuff. When, 60 years ago, the world's population was about 2.5 billion, worries about water supply affected
柑橘的功效relatively few people. Both drought and hunger existed, as they have throughout history, but most people could be fed without irrigated farming. Then the green revolution,in an inspired combination of new crop breeds, fertilizers and water, made possible a huge ri in the population. The number of people on Earth ro to 6 billion in 2000, nearly 7 billion today, and is heading for 9 billion in 2050. The area under irrigation has doubled and the amount of water drawn for farming has tripled. The proportion of people living in countries chronically short of water is t to ri from 8% at the turn of the 21st century to 45% by 2050.
4.Farmers' increasing demand for water is caud not only by the growing number of mouths to be fed but also by people's desire for better-tasting, more interesting food. Unfortunately, it takes nearly twice as much water to grow a kilo of peanuts as a kilo of soybeans, nearly four times as much water to produce a kilo of beef as a kilo of chicken. With 2 billion people around the world about to enter the middle class, the agricultural demands on water would increa even if the population stood still.
5.Industry, too, needs water. It takes about 22% of the world's withdrawals. Domestic activities take the other 8%. Together, the demands of the two categories quadrupled in the cond half of the 20th century, growing twice as fast as tho of farming.
6.Meeting that demand is a difficult task. One reason is that the supply of water is finite. The world will have no more of it in 2025 or 2050 than it has today, or when it lapped at the sides of Noah's Ark. This is becau the law of conrvation of mass says, broadly, that however you u it, you cannot destroy the stuff. Neither can you readily make it. If some of it ems to come from the skies, that is becau it has evaporated from the Earth's surface, condend and returned.
7.Most of this surface is a, and the water below it—over 97% of the total on Earth—is salty. In principle, the salt can be removed to increa the supply of fresh water, but at prent desalination is expensive and us lots of energy.
8.Of the 2.5% of water that is not salty, about 70% is frozen, either at the poles, in glaciers or in permafrost. So all living things, except tho in the a, have about 0.75% o孕妇能喝红茶吗
f the total to survive on. Most of this available water is underground, in aquifers or similar formations. The rest is falling as rain, sitting in lakes and rervoirs or flowing in rivers where it is, with luck, replaced by rainfall and melting snow and ice. There is also, take note, water vapor in the atmosphere.
9.The value of water as a commodity of cour varies according to locality, purpo and circumstance. Take locality first. Water is not evenly distributed—just nine countries account for 60% of all available fresh supplies—and among them only Brazil, Canada, Colombia, Congo, Indonesia and Russia have an abundance. America is relatively well off, but China and India, with over a third of the world's population between them, have less than 10% of its water.
10.Even within countries the variations may be huge. The average annual rainfall in 读书笔记大学India's northeast is 110 times that in its western dert. And many places have plenty of water, or even far too much. Flooding is routine, and may become more frequent and damaging with climate change.
11.Scarce or plentiful, water is above all local. It is heavy—one cubic water weighs a tonne—, so expensive to move. Surface water—mostly rivers, lakes and rervoirs—will not flow from one basin into another without artificial diversion, and usually only with pumping. Within a basin, the water upstream may be uful for irrigation, industrial or domestic u. As it nears the a, though, the opportunities diminish to the point where it has no us except to sustain deltas, wetlands and to carry silt out to a.
