Unit 9   

    There's a famous saying that goes: "Everybody talks about the weather, but no one ever does anything about it!" Humans do, of course, affect the climate, as we know from scientists' warnings about everything from the greenhouse effect to nuclear winter. Conscious of our power to harm the environment, we can sometimes forget that as a species we are still helpless to control -- or even predict with any accuracy -- many of the powerful surprises that nature can spring on us. The first two texts in this unit examine the causes and effects of one of the world's most trouble-making natural environmental phenomena -- El Niño -- while Text C speculates about what factors are making our weather so wild, and what we might be able to do about it.

Text  A

    In March of 1997, Stephen Zebiak stared at his computer screen in alarm. The veteran climate researcher saw indications of a worldwide weather event that, over the years, has been blamed for droughts and floods, famine, fires and thousands of deaths. Called El Niño, it is the most disruptive climatic phenomenon on the planet.

     Zebiak and Mark Cane, research scientists at Columbia University, had developed a computerized forecast model that correctly predicted El Niño's occurrences in 1982, '86 and '91, and it had pointed to a recurrence in '98. But the data appearing on Zebiak's screen from satellite and sea-surface monitors across the Pacific were unmistakable: El Niño was already beginning. A huge pool of warm water -- larger than the United States and some 600 feet deep -- was moving slowly but surely eastward toward South America.

    In June the equatorial trade winds reversed direction from westward to eastward. By September, waters off Northern California were roughly 17 degrees warmer than normal. Off the Washington coast, stunned fishermen caught tropical fish that seldom stray that far north. Storms were flooding central Chile, and heavier-than-normal snowfalls in the Andes trapped hundreds in the bitter cold. And all of this only foretold of even more devastating weather for the fall and winter.

    El Niño means "little boy" in Spanish; when capitalized, it refers to the Christ child. This innocent-sounding name originated in the 19th century, when Peruvian sailors noticed that every few years around Christmastime, waters near the coasts warmed up and the current shifted southward. But this "little boy" plays havoc around the globe.

  El Niño occurs when weather patterns in the tropical Pacific shift violently. Normally, strong westward-blowing trade winds off South America push surface water toward Asia. Just as blowing on hot coffee pushes the liquid up against the opposite side of the cup, the trade winds pile warm water against the coastlines of Australia, Indonesia and the Philippines. Above the warm water, moist air rises, lowering atmospheric pressure and triggering the tropical showers that nourish the rain forests of Asia. Meanwhile high-altitude winds travel back toward South America. There, the cooled air sinks, raising atmospheric pressure and suppressing rain along most of the Pacific coast, making it one of the driest regions in the world.

  But with El Niño, the pattern reverses. Atmospheric pressure in the Western Pacific rises, setting the stage for drought from Australia to India. The trade winds decrease, or in extreme years reverse to blow eastward. As a result, a huge mass of warm water flows back toward South America, causing storms from Chile to California. Meanwhile, over the Pacific, ten-mile-high storm clouds further heat the atmosphere, fueling a stronger-than-normal jet stream, which often splits in two. One branch moves north, warming the Pacific Northwest, central Canada and Alaska. Another branch surges south, producing heavy rains in the U.S. Gulf States and Southwest.

  El Niño's vast impact on humans has often been catastrophic. The El Niño of 1982-83 inflicted $13 billion in damage and claimed some 2,000 lives. In Australia day turned to night when a dust storm blanketed Melbourne; brush fires raged in its wake. In place of its normal monsoon, Southern India got dried-up crops and the threat of mass starvation. At the same time, violent rainstorms devastated the Western Hemisphere: Peru's fishing industry -- once one of the richest in the world -- was wiped out, and seaside towns were washed into the Pacific.

  Is there a good side to El Niño? There can be. Zebiak notes that the number of tropical hurricanes in the Atlantic is reduced during an El Niño year. One theory is that winds created by El Niño shear off the tops of Atlantic hurricanes, aborting them before they reach full force. And a team of scientists in Israel who study tree rings and satellite cloud pictures concluded that El Niño may bring precious moisture to the thirsty Middle East. “It is perhaps fitting that El Niño -- the Christ child -- should have a link to the Holy Land,” notes scientist Dan Yakir.

   This year, scientists around the world are keeping a sharp eye on El Niño. They know that the greater the temperature rise in Pacific waters off South America, the more powerful the El Niño. And this year's waters have heated up unusually fast. Climate-change researcher Michael Ghil of UCLA expects the impact to be “substantial.” Ants Leetmaa, director of the National Oceanic and Atmospheric Administration's Climate Prediction Center in Maryland, agrees: This El Niño is shaping up as one of the most powerful ever.

    According to forecasters, hardest hit in this country will likely be California, where heavy rains can send houses sliding down muddy slopes onto washed-out coastal highways. The nation's southern states -- from California to Florida -- can expect cooler and wetter weather than normal this winter and spring, with extensive storms in some areas. The Northwest should be warmer and drier than normal.

     Wetter-than-normal conditions are expected in much of South America. The Asian monsoon rains could fail, resulting in food shortages in India. In Australia, where El Niño typically means drought, strict water conservation is already under way.

     El Niño's effects won't just be climatic, of course -- the global economy is sure to suffer as well. Drought in Brazil and flooding in Colombia may result in higher prices for coffee and other crops. And fishing industries from Ecuador to California are already being hurt.

     Clearly, the more accurately scientists can forecast El Niño, the more people everywhere can prepare. Insurance companies, farmers, power and irrigation companies, public-safety agencies and even tourist boards could benefit from knowing in advance when El Niño will strike.

    “Reliable forecasting is still in its infancy,”states Mark Cane. Someday, perhaps, scientists will be able to predict exactly how El Niño will behave. But for now, batten down the hatches and get ready for some wild weather!

珀·奥拉 埃米莉·多莱尔

   1997年3月，斯蒂芬·泽比埃克惊恐地盯着电脑屏幕看。这位经验丰富的气候研究人员发现了一种全球性气象活动的迹象，这种气象活动多年来一直被认为是造成干旱、洪涝、饥荒、火灾及成千上万人丧生的罪魁祸首。它被称作厄尔尼诺现象，是地球上破坏性最大的气候现象。

     泽比埃克和马克·凯恩是哥伦比亚大学的科学研究人员，他们研制了一种电脑化预报模型，曾准确地预测到1982年、1986年和1991年厄尔尼诺现象的发生，并且表明1998年还可能再次发生。但是显示在泽比埃克电脑屏幕上从卫星和太平洋上的海面监控器传来的数据明确无误：厄尔尼诺现象已经开始了。一个巨大的暖水区----大于美国，水深600英尺左右----正在缓慢地但确定无疑地向东往南美移动。

   6月，赤道信风调转风向，由西风转为东风。到了9月，北加利福尼亚近海水域的水温比平时高出17度左右。在华盛顿州的近海水域里，目瞪口呆的渔民们捕到了很少离群远游北上的热带鱼。暴风雨造成了智利中部的洪涝，而安第斯山脉非同寻常的大雪将数百人困在严寒之中。这一切只不过预示着秋冬两季将会出现毁灭性更大的天气。

      厄尔尼诺在西班牙语中意为“小男孩”；首字母大写时指幼年基督。这个听起来天真无邪的名字产生于19世纪，当时秘鲁的水手们注意到每隔几年在圣诞节前后近海水域就会变暖，水流则改变方向向南。可是这个“小男孩”却在全球到处肆意破坏。

   当热带太平洋地区的天气模式变化剧烈时，就会发生厄尔尼诺现象。通常，南美洲沿海强劲的西向信风将表面的海水吹向亚洲。就像对着热咖啡吹气会将咖啡吹上对面的杯壁一样，信风使温暖的海水涌向澳大利亚、印度尼西亚和菲律宾的海岸线。在温暖的海水上面，潮湿的空气上升，使大气压降低并引起热带暴雨，滋润着亚洲的雨林。同时，高空气流向南美洲回移。在那儿，受到冷却的空气下沉，使大气压升高并遏制了太平洋大部分沿岸的降雨， 使之成为世界上最干旱的地区之一。

   但是有了厄尔尼诺现象，天气模式正好相反。西太平洋的大气压升高，为澳大利亚到印度的干旱创造了条件。信风减弱，或者在极端年份里改向东吹。结果，一片巨大的暖水向南美洲回流，造成智利到加利福尼亚一带的暴风雨。同时，在太平洋上空，高达10英里的暴风云使大气进一步升温，引起一股异常强大的急流。这股急流常常一分为二。一支向北，使太平洋西北部、加拿大中部以及阿拉斯加变暖。另一支汹涌向南，在美国濒墨西哥湾诸州及西南部造成大量降雨。

   厄尔尼诺现象对人类的巨大影响常常是灾难性的。1982年到1983年发生的那次厄尔尼诺现象造成了130亿美元的损失，夺去了约2000人的生命。在澳大利亚，一场尘暴铺天盖地袭击了墨尔本，白昼变成了黑夜；随之而来的是熊熊的丛林大火。印度南部没有等来通常的季风；庄稼枯萎了，面临的是大规模的饥馑。与此同时，猛烈的暴雨给西半球造成了巨大的破坏。秘鲁的渔业----曾是世界上最富饶的渔业之一----被彻底摧毁了，滨海城镇被冲进了太平洋。

   厄尔尼诺现象有没有好的一面呢? 有时候是有的。泽比埃克注意到在出现厄尔尼诺现象的年头里，大西洋热带飓风的发生次数减少了。一种理论是：厄尔尼诺造成的气流削掉了大西洋飓风的前锋，使它们还没来得及大施淫威就半途夭折。以色列的一组研究树木年轮和卫星云图的科学家得出结论认为，厄尔尼诺现象可能会为干旱的中东地区带来宝贵的水气。科学家丹·亚克指出:"厄尔尼诺，也就是幼年基督，应该与圣地有关，这或许是很合适的。"

   今年，世界各地的科学家都在密切注意着厄尔尼诺现象。他们知道南美洲沿海太平洋水域的升温越高，厄尔尼诺现象就越强劲。而今年水域的升温异常迅速。加利福尼亚大学洛杉矶分校的气候变化研究员迈克尔·吉尔预计，厄尔尼诺现象的影响将是“巨大的”。马里兰州的国家海洋与大气管理局气候预测中心主任安茨·利特马看法相同：这次的厄尔尼诺现象正在发展成为迄今最为严重的一次。

   根据预测人员的说法，美国受灾最重的可能是加利福尼亚州，那儿的大雨能使房屋沿着泥泞的斜坡滑到洪水冲蚀的沿岸公路上。美国的南部各州----从加利福尼亚到佛罗里达----今冬明春的天气预计可比往年更寒冷、更潮湿，有些地区会有大面积的暴风雨。西北地区则应比常年更温暖、更干燥。

   南美洲的大部分地区预计会出现比平时更加潮湿的气候条件。亚洲的季风可能不会降临，从而造成印度的粮食短缺。在澳大利亚，厄尔尼诺现象总是意味着干旱，因此已开始实行严格的节约用水。

      当然，厄尔尼诺现象的影响当然不限于气候方面----全球经济无疑也会受到损害。巴西的干旱和哥伦比亚的洪涝可能导致咖啡和其他作物的价格上涨。从厄瓜多尔到加利福尼亚的渔业已经受到了危害。

   显然，科学家们越是能准确地预报厄尔尼诺现象，各地的人们就越是能作好准备。如果事先能知道厄尔尼诺现象的发生时间，那么保险公司、农民、电力和灌溉公司、公共安全机构，乃至旅游局都可能从中获益。

    “可靠的预测仍处于初始阶段，”马克·凯恩声言。也许有一天科学家们能够准确地预报厄尔尼诺现象的具体表现。但目前则应未雨绸缪，为应付恶劣的天气作好准备。