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  • 人口飞速增长给粮食供应带来了巨大的压力
  • 2014/5/20 9:47:06
  •  在这个欲望无穷、挥霍无度的年代里提粮食危机,有多少人会觉得危言耸听?然而,摆在我们面前的不可否认的事实是,各国粮食价格上涨屡创新高,粮食减产消息不断爆出,因粮食短缺和价格上涨而产生的骚乱此起彼伏。粮食危机就像一场无声的海啸,不断向全球各个角落袭来,闹得世界动荡不安……

    As the year 2011 begins, the price of wheat is setting an all-time high in the United Kingdom. Food riots are spreading across Algeria. Russia is importing grain to sustain its cattle herds until spring grazing begins. India is wrestling with an 18-percent annual food inflation rate, sparking protests. The Mexican government is buying corn futures1) to avoid unmanageable tortilla2) price rises. And on January 5, 2011, the U.N. Food and Agricultural organization announced that its food price index for December hit an all-time high.
    But whereas in years past it’s been weather that has caused a spike in commodities prices, now it’s trends on both sides of the food supply/demand equation that are driving up prices. On the demand side, the culprits3) are population growth, rising affluence, and the use of grain to fuel cars. On the supply side: soil erosion4), aquifer5) depletion6), the loss of cropland to nonfarm uses, the diversion of irrigation water to cities, the plateauing7) of crop yields in agriculturally advanced countries, and—due to climate change—crop-withering heat waves and melting mountain glaciers and ice sheets. These climate-related trends seem destined to take a far greater toll8) in the future.
    There’s at least a glimmer9) of good news on the demand side: World population growth, which peaked at 2 percent per year around 1970, dropped below 1.2 percent per year in 2010. But because the world population has nearly doubled since 1970, we are still adding 80 million people each year. At some point, this relentless growth begins to tax10) both the skills of farmers and the limits of the earth’s land and water resources.
    Beyond population growth, there are now some 3 billion people moving up the food chain, eating greater quantities of grain-intensive livestock and poultry products. The rise in meat, milk, and egg consumption in fast-growing developing countries has no precedent.
    The third major source of demand growth is the use of crops to produce fuel for cars. In the United States, which harvested 416 million tons of grain in 2009, 119 million tons went to ethanol distilleries11) to produce fuel for cars. That’s enough to feed 350 million people for a year. In Europe, where much of the auto fleet runs on diesel12) fuel, there is growing demand for plant-based diesel oil, principally from rapeseed and palm oil. This demand for oil-bearing crops is not only reducing the land available to produce food crops in Europe, it is also driving the clearing of rainforests in Indonesia and Malaysia for palm oil plantations.
    The combined effect of these three growing demands is stunning: a doubling in the annual growth in world grain consumption from an average of 21 million tons per year in 1990~2005 to 41 million tons per year in 2005~2010.
    While the annual demand growth for grain was doubling, new constraints were emerging on the supply side, even as13) longstanding ones such as soil erosion intensified. An estimated one third of the world’s cropland is losing topsoil faster than new soil is forming through natural processes—and thus is losing its inherent productivity. Two huge dust bowls14) are forming, one across northwest China, western Mongolia, and central Asia; the other in central Africa. Each of these dwarfs15) the U.S. dust bowl of the 1930s. Satellite images show a steady flow of dust storms leaving these regions, each one typically carrying millions of tons of precious topsoil. In countries with severe soil erosion, such as Mongolia and Lesotho, grain harvests are shrinking as erosion lowers yields and eventually leads to cropland abandonment. The result is spreading hunger and growing dependence on imports.
    Meanwhile aquifer depletion is fast shrinking the amount of irrigated area in many parts of the world; this relatively recent phenomenon is driven by the large-scale use of mechanical pumps to exploit underground water. Today, half the world’s people live in countries where water tables16) are falling as overpumping depletes aquifers. Sooner or later, falling water tables translate into rising food prices.
    Irrigated area is shrinking in the Middle East, notably in Saudi Arabia, Syria, Iraq, and possibly Yemen. In Saudi Arabia, which was totally dependent on a now-depleted fossil aquifer for its wheat self-sufficiency, production is in a free fall17). From 2007 to 2010, Saudi wheat production fell by more than two thirds. By 2012, wheat production will likely end entirely, leaving the country totally dependent on imported grain.
    The Arab Middle East is the first geographic region where spreading water shortages are shrinking the grain harvest. But the really big water deficits are in India, where the World Bank numbers indicate that 175 million people are being fed with grain that is produced by overpumping18). In China, overpumping provides food for some 130 million people.
    The last decade has witnessed the emergence of yet another constraint on growth in global agricultural productivity: the shrinking backlog19) of untapped20) technologies. In some agriculturally advanced countries, farmers are using all available technologies to raise yields. In Japan, the first country to see a sustained rise in grain yield per acre, rice yields have been flat now for 14 years. Rice yields in South Korea and China are now approaching those in Japan.
    A similar situation is emerging with wheat yields in Europe. In France, Germany, and the United Kingdom, wheat yields are no longer rising at all. These three countries together account for roughly one-eighth of the world wheat harvest.
    Another trend slowing the growth in the world grain harvest is the conversion of cropland to nonfarm uses. Suburban sprawl21), industrial construction, and the paving of land for roads, highways, and parking lots are claiming cropland in the Central Valley of California, the Nile River basin in Egypt, and in densely populated countries that are rapidly industrializing, such as China and India.
    Fast-growing cities are also competing with farmers for irrigation water. In areas where all water is being spoken for22), such as most countries in the Middle East, northern China, the southwestern United States, and most of India, diverting water to cities means less irrigation water available for food production.
    The rising temperature is also making it more difficult to expand the world grain harvest fast enough to keep up with the record pace of demand. Crop ecologists have their own rule of thumb23): For each 1 degree Celsius rise in temperature above the optimum24) during the growing season, we can expect a 10 percent decline in grain yields. This temperature effect on yields was all too visible in western Russia during the summer of 2010 as the harvest was decimated25) when temperatures soared far above the norm.
    Another emerging trend that threatens food security is the melting of mountain glaciers. Over the long term, melting ice sheets in Greenland and West Antarctica, combined with thermal expansion of the oceans, threaten to raise the sea level by up to six feet during this century. Even a three-foot rise would inundate half of the riceland in Bangladesh. It would also put under water much of the Mekong Delta that produces half the rice in Vietnam, the world’s number two rice exporter. Altogether there are some 19 other rice-growing river deltas in Asia where harvests would be substantially reduced by a rising sea level.
    The current surge in world grain and soybean prices, and in food prices more broadly, is not a temporary phenomenon. We can no longer expect that things will soon return to normal, because in a world with a rapidly changing climate system there is no norm to return to.
    The unrest today is no longer conflict between heavily armed superpowers, but rather spreading food shortages and rising food prices that threatens our global future. Unless governments quickly redefine security and shift expenditures from military uses to investing in climate change mitigation, water efficiency, soil conservation, and population stabilization, the world will in all likelihood26) be facing a future with both more climate instability and food price volatility27).

    2011年伊始,英国小麦价格创下历史新高;粮食问题引发的骚乱席卷阿尔及利亚;俄罗斯依靠进口粮食饲养牲畜,直至春季放牧期来临;印度疲于应付18%的粮食年通货膨胀率,引来怨声载道;墨西哥政府买入玉米期货,以防玉米粉圆饼价格上涨失控。2011年1月5日,联合国粮农组织宣布,2010年12月粮食价格指数升至空前高位。
    在过去的数年时间里,导致商品价格飙升的一直是气候因素;而现在,助推粮食价格上扬的则是供求两端的变化趋势。就需求而言,抬高粮价的“罪魁”是人口增长、日益提高的富裕程度以及汽车对谷物燃料的使用。从供应来看,造成粮价上涨的“祸首”是土壤侵蚀、蓄水层耗竭、非农业用地对农田的侵占、灌溉用水向城市的分流、农业发达国家农作物产量的停滞不前,以及(气候变化引起的)使农作物枯萎的热浪和高山冰川与冰原的消融。这些与气候变化相关的发展趋势也许注定会在将来造成更大的损失。
    从需求方面来看,我们至少还能隐约看到一线曙光:全球人口年增长率在1970年前后达到2%的峰值,而到2010年终于降至1.2%以下。不过,由于全球人口自1970年以来几乎翻了一番,因此,地球上每年增加的人口还是有八千万之多。到了一定时候,人口的不断增长会让农民的生产技能与有限的地球水土资源都不堪重负。
    除了人口增长的因素外,还有约三十亿人在食物链中的位置不断提升,他们吃掉了比以往更多的牲畜和家禽制品,而这些牲畜和家禽皆以粮食为食。在发展迅猛的发展中国家,肉、奶、蛋的消耗量
    出现了史无前例的增长。
    粮食需求量增长的第三个主要原因是谷物被用来制造汽车燃料。以美国为例,2009年美国的谷物收成达到4.16亿吨,其中1.19亿吨被投放到乙醇蒸馏厂用于生产汽车燃料,而这些谷物足够供3.5亿人作一年的口粮。在欧洲,大多数汽车以柴油为燃料,因此对以植物为原料的柴油的需求日益增长,主要是菜籽油和棕榈油。对油料作物的这一需求不仅使欧洲可供粮食作物生长的土地面积减少,而且也导致印度尼西亚和马来西亚的热带雨林因为种植产油的棕榈树而遭到大面积砍伐。
    这三种不断增长的需求结合在一起产生的影响令人震惊:全球谷物年消耗量翻了一番,从1990~2005年间的平均每年2100万吨上升至2005~2010年间的4100万吨。
    谷物的年需求量在成倍增长,但在供应方面,新的制约因素却不断出现,而且正赶上由来已久的土壤侵蚀问题进一步加剧。据估算,全球1/3的耕地的表层土壤正在流失,流失的速度超过了新土壤层自然形成的速度,这些耕地由此逐渐失去了其固有的生产力。目前,两个巨大的尘暴区正在形成,一个覆盖中国西北部、蒙古西部和中亚地区,另一个位于非洲中部。与这两者相比,美国20世纪30年代形成的尘暴区相形见绌。卫星图像显示,从这些地域刮起的沙尘暴连绵不绝,通常每次都带走数百万吨宝贵的表层土壤。在土壤侵蚀问题非常严重的蒙古、莱索托等国,粮食收成日趋减少,原因就在于土壤侵蚀致使粮食减产,并最终导致农田废弃。由此引发的结果是饥荒的四处蔓延和对进口的日益依赖。
    与此同时,蓄水层的枯竭也导致世界许多地方的灌溉面积迅速缩减。这一新近才出现的现象归咎于人们大规模地使用机械泵来开采地下水。如今,由于过量取水造成蓄水层消耗殆尽,全世界有一半的人生活在地下水位持续下降的国家。而地下水位下降迟早会引起粮食价格上涨。
    中东地区的灌溉区正在不断缩小,情况严重的国家包括沙特阿拉伯、叙利亚和伊拉克,可能还有也门。沙特是一个完全依赖化石蓄水层实现小麦自给自足的国家,现在由于蓄水层枯竭,小麦产量开始直线下降。2007年至2010年,沙特的小麦产量减少了不止2/3。到2012年,沙特的小麦有可能彻底绝收,整个国家的谷类粮食也将因此而完全依赖进口。
    中东的阿拉伯地区是最早因水资源普遍短缺而造成粮食歉收的地区。然而,缺水问题真正严重的国家是印度。世界银行的数据显示,该国有1.75亿人依靠过度取水生产的粮食养活。在中国,大约1.3亿人依靠过度取水来获取口粮。
    在过去十年间,还有另外一种制约因素限制了全球农业生产力的发展:新技术后继乏力。在一些农业发达国家,农民都只是利用现成的所有技术来提高农作物产量。作为第一个实现粮食亩产持续增长的国家,日本的大米产量已经“原地踏步”了14年之久,韩国和中国的大米产量现已快赶上日本。
    欧洲的小麦产量也面临类似的处境。在法国、德国和英国,小麦的产量不再有丝毫增长。而这三个国家的小麦产量总和约占全世界的1/8。
    另一个导致全球粮食产量增长放缓的因素是农业耕地向非农业用地的转换。在加利福尼亚中央峡谷、埃及尼罗河盆地以及中国、印度等迅速朝着工业化迈进的人口密集型国家,城郊扩张、工业建设以及公路、高速路和停车场的铺建都在纷纷侵占农田。
    快速发展的城市也开始与农民争抢灌溉用水。在所有亟待用水的地方,比如中东大多数国家、中国北部、美国西南部以及印度大部分地区,引水入城就意味着可供粮食生产的灌溉用水将越来越少。
    气温的不断上升也使得全球谷物产量难以跟上空前增速的需求步伐。农作物生态学家们有这样一个经验法则:在种植季节,以适宜农作物生长的最佳温度为基准,气温每上升1℃,粮食就可能减产10%。这一温度效应在2010年夏季的俄罗斯西部地区表现得极其显著,当时气温急速攀升,远远超过正常值,致使粮食大大减产。
    威胁粮食安全的另一个新趋势是高山冰川的不断融化。从长远看,格陵兰岛和南极洲西部冰盖的消融,加上海洋的热膨胀,极有可能在本世纪内导致海平面上升六英尺之高。事实上,海平面只需上升三英尺,孟加拉国一半的稻田就会被海水淹没,湄公河三角洲的大部分地区也会成为一片汪洋。而越南作为世界第二大粮食出口国,其一半的粮食产自湄公河三角洲。海平面的上升还会使亚洲大约十九个产稻三角洲大幅减产。
    目前,全世界范围内谷物、大豆以及更宽泛意义内食品价格的飙涨并不是一个暂时现象。我们不能再指望一切会很快恢复正常,因为在一个气候体系快速变化的世界里,正常已成为无稽之谈。
    造成当今世界动荡不安的不再是武器大国之间的纷争,而是日益普遍的粮食短缺和不断增长的粮食价格,这些问题已对全球的未来构成威胁。各国政府须当机立断,重新定义安全问题,减少军用支出,加大在缓和气候变化、提高用水效能、保护土壤以及稳定人口增长方面的投入。否则,世界将极有可能面临一个气候和粮食价格都变幻莫测的未来。

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