New Directions: Megacities and global change

摘要

Perhaps 3% of the world's population lived in cities around the year 1800 (Brunn and Williams, 1983. Cities of the World. HarperCollins, New York, 506pp.). Subsequently, industrialization and urbanization intensified during the "Anthropocene" (Crutzen, 2002. Nature 415, 23) in the fossil fuel based economy (or carbon-economy). As a result, by 1900 the urban population fraction had increased to 13%, and to 47% by 2000 (UN, 2004; see reference in Table 1). Over the last 50 years, the world's urban population has grown faster (～ 2.7% yr~(-1)) than the total population (～ 1.8% yr~(-1)). This trend is likely to continue in the foreseeable future marking for the first time in human history that the world will have more urban than rural residents by 2007. The striking offshoots of rapid-and-massive urbanization are the megacities that emerged as a most visible physical sign of anthropogenic global change in the 20th century. In 1950, there were only two megacities, New York and Tokyo with 12.4 and 11.3 million people, respectively. At present there are 20 megacities with a combined population of 283 million (UN, 2004).