Unit 20 New Frontiers【美文阅读】 Our world in 2050尽管人类在改造大自然方面已取得了不少成绩，但是人类频繁的活动已使今日的地球失去了原有的艳丽姿色。When scientists scan the global horizon ， over － fishing ， loss of species habitat，water shortage，climate change，and invasive(侵害的)species look to be the biggest threats to the earth.What will our world be like in 2050?Population decrease and increaseThere are two features in the growth of world population.First，the annual increase in population in 15 European countries ，in the past few years ，has been only 300,000.The United Nations estimates that by 2050，the population of European countries will decrease from the current 0.72 billion to 0.63 billion.Second，the population in developing countries is growing rapidly.Over the past 50 years，the rate of increase in population has been fastest in the least developed countries.By 2050 ， the population of Africa is expected to reach 1.8 billion,0.9 billion more than its current population.Global warmingA recent research report indicates that it is quite possible that the Earth's temperature is rising well above the previous estimate.Such a result would have severe consequences(后果)．A research team from the University of Colorado used satellite data to estimate that the ice sheet will lose up to 48 cubic miles by 2050.Ice shelves in the Antarctic will have decreased by more than 7,200 square miles in the next four decades.Water shortageAfrica's rivers face dramatic(戏剧性的) change that will leave a quarter of the continent severely short of water by the middle of the century.“In those areas where there is already a water shortage，it's going to have a devastating(毁灭性的) effect，”the study says.“If you're now walki...
