Reading comprehension-从冰山中获取淡水
[p=30, 2, center][b]Obtaining Fresh Water from Icebergs[/b][/p]The concept of obtaining fresh water from icebergs that are towed to populated areas and arid regions of the world was once treated as a joke more appropriate to cartoons than real life. But now it is being considered quite seriously by many nations, especially since scientists have warned that the human race will outgrow its fresh water supply faster than it runs out of food.
Glaciers are a possible source of fresh water that has been overlooked until recently. Three-quarters of the Earth's fresh water supply is still tied up in glacial ice, a reservoir of untapped fresh water so immense that it could sustain all the rivers of the world for 1,000 years. Floating on the oceans every year are 7,659 trillion metric tons of ice encased in 10,000 icebergs that break away from the polar ice caps, more than ninety percent of them from Antarctica.
Huge glaciers that stretch over the shallow continental shelf give birth to icebergs throughout the year. Icebergs are not like sea ice, which is formed when the sea itself freezes, rather, they are formed entirely on land, breaking off when glaciers spread over the sea. As they drift away from the polar region, icebergs sometimes move mysteriously in a direction opposite to the wind, pulled by subsurface currents. Because they melt more slowly than smaller pieces of ice, icebergs have been known to drift as far north as 35 degrees south of the equator in the Atlantic Ocean. To corral them and steer them to parts of the world where they are needed would not be too difficult.
The difficulty arises in other technical matters, such as the prevention of rapid melting in warmer climates and the funneling of fresh water to shore in great volume. But even if the icebergs lost half of their volume in towing, the water they could provide would be far cheaper than that produced by desalinization, or removing salt from water. [p=30, 2, center][b]从冰山中获取淡水[/b][/p]
把冰山拖到世界上人口稠密的地区和干旱地带，再从中获取淡水，这个想法曾一度被认为是一个笑话，更适合于卡通画，而非现实生活。然而现在，许多国家正相当认真地考虑这件事情，特别是在[u][b][color=#16387c]科学[/color][/b][/u]家们发出警告之后。科学家们认为人类将在耗尽粮食之前首先耗尽淡水资源。
冰川是一个直到最近以前一直被忽视的可能的淡水源。全球四分之三的淡水还锁在冰川的冰块中。冰川就是一个蓄水池，其中未开发的淡水量是如此巨大，足够支持全世界的江河1000 年。每年有7，659 万亿公吨冰漂流在海洋中。它们包含在10，000 座从极地冰帽中断裂出来的冰山中。这些冰山的90%以上来自南极。
一年四季里，覆盖在浅层大陆架上的巨大冰川生成了众多冰山。冰山和海水的冰不同，后者是海水自身结冰形成的，而冰山则完全是在陆地上形成的。当冰川伸展到海水中时，冰山就断裂下来。当漂离极地地区时，冰山有时会在底层洋流的推动下颇为神秘地逆风移动。由于冰山比小块的冰融化要慢，因此有的冰山在大西洋中向北飘到了赤道以南35°的地方。把冰山蓄拦起来并拖到世界上需要它们的地方将不会太困难。
有困难的是其它的技术事宜。比如，如何防止冰山在较暖的气候中迅速融化以及如何把大量的淡水收集到岸上去。但是，即便在拖的过程中冰山失去了一半体积，这样做也远比从海水中脱盐取得淡水便宜。
页:
[1]