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1、Decades of drought in central Africa reached their worst point in the 1980s, causing Lake Chad, a shallow lake used to water crops in neighboring countries, to almost dry out completely. The shrinking lake and prolonged drought was initially blamed onovergrazing（过度放牧）and bad agricultural practices.
2、More recently, Lake Chad became an example of global warming. New University of Washington research, to be published in Geophysical Research Letters, shows that the drought were caused at least in part by Northern Hemisphere air pollution.Aerosols emanating from coal-burning factories in the United
3、States and Europe during the 1960s, 70s and 80s cooled the entire Northern Hemisphere, shifting tropical rain bands south. Rains no longer reached the Sahel region, a band that spans the African continent just below the Sahara desert.When clean-air legislation passed in the U.S. and Europe, the rain
4、 band shifted back, and the drought lessened. Related research by the UW researchers and their collaborators shows that global warming is now causing the land-covered Northern Hemisphere to warm faster than the Southern Hemisphere, further reversing the pre-1980s trend.Previous research has suggeste
5、d a connection between coal-burning and the Sahel drought, but this was the first study that used decades of historical observations to find that this drought was part of a global shift in tropical rainfall, and then used multiple climate models to determine why.One of our research strategies is to
6、zoom out, said lead author Yen-Ting Hwang, a UW doctoral student in atmospheric sciences. Instead of studying rainfall at a particular place, we try to look for the larger-scale patterns.To determine that the Sahel drought was part of a broader shift, the authors looked at precipitation from all rai
7、n gauges that had continuous readings between 1930 and 1990. Other places on the northern edge of the tropical rain band, including northern India and South America, also experienced dryer climates in the 1970s and 80s. Meanwhile, places on the southern edge of the rain band, such as northeast Brazi
8、l and the African Great Lakes, were wetter than normal.To understand the reason, authors looked at all 26 climate models used by the Intergovernmental Panel on Climate Change. Researchers discovered that almost all the models also showed some southward shift, and that cooling fromsulfate（硫酸盐）aerosol
9、s in the Northern Hemisphere was the primary cause.We think people should know that these particles not only pollute air locally, but they also have these remote climate effects, Hwang said.在20世纪80年代，几十年来在中部非洲的干旱达到他们的最坏点，造成浅水湖泊用于水作物邻国，乍得湖几乎完全干涸。湖泊萎缩和长期干旱最初归咎于过度放牧（过度放牧）和坏的农业实践。最近，乍得湖成为全球变暖的一个例子。新华盛顿大
10、学科研项目，发表在“地球物理研究快报显示，干旱造成至少部分由北半球的空气污染。来自烧煤的工厂，在美国和欧洲在20世纪60年代，70年代和80年代的气溶胶冷却的整个北半球，南方热带雨林带转移。不再下雨达到萨赫勒地区，一个乐队，横跨撒哈拉大沙漠的非洲大陆正下方。通过在美国和欧洲的清洁空气立法时，雨带移回，减轻旱情。威斯康星大学的研究人员和他们的合作者的相关研究表明，全球变暖正在造成土地覆盖北半球比南半球温暖更快，进一步扭转了20世纪80年代以前的趋势。此前有研究表明燃煤和萨赫勒地区的干旱之间的连接，但是这是第一次使用了几十年的历史观测研究发现，这次旱灾是一个全球性的转变在热带降雨，然后使用多个气候
11、模型，以确定为什么。“我们的研究策略之一是缩小，说：”主要作者黄颜婷大气科学，华盛顿大学的博士生。“与其研究在某一特定地点的降雨，我们尽量寻找较大规模的模式。”要确定萨赫勒地区的干旱是一个更广泛的转变的一部分，看着降水雨量器，在1930年和1990年之间有连续的读数。其他地方，包括印度北部和南美洲的热带雨林带的北部边缘，在20世纪70年代和80年代也经历了干燥的气候。同时，雨带的南部边缘的地方，如巴西东北部和非洲大湖，较正常多雨。要明白其中的道理，笔者看了由政府间气候变化小组在所有26个气候模型。研究人员发现，几乎所有的车型也表现出一些南移，从硫酸的冷却（硫酸盐）在北半球气溶胶的首要原因。，“黄禹锡说：”我们认为人们应该知道，这些粒子不仅污染当地空气，但他们也有这些偏远的气候影响。“成千上万人疯狂下载。更多价值连城的绝密英语学习资料，洛基内部秘密英语，技巧，策略请在 网上 申请报名”
