长期以来,许多国家的专家一直认为,撒哈拉大沙漠正在不断向南扩大,吞噬掉大片大片的良田。生态学家们甚至警告说:撒哈拉沙漠对周围土地的蚕食正是全球“沙漠化”的一大例证。但近年来美国人造卫星对撒哈拉沙漠的观测却显示,撒哈拉沙漠并非“不断扩大”,而是“时大时 For a long time, experts from many countries have always believed that the Sahara Desert is constantly expanding southward and engulfing large tracts of farmland. Ecologists even warned that the encroachment of the surrounding land by the Sahara desert is a great example of global “desertification.” However, observations made by the U.S. satellite in the Sahara Desert in recent years have shown that the Sahara Desert is not “expanding” but "