让情况更复杂的是，未来几十年中，由于人口结构变化、人口增加、城市化、国家内部移民、全球化、贸易自由化和发展中世界中产阶级的迅速扩张，这些问题的背景可能发生重大变化。
Complicating matters further, these problems’ backdrop is likely to change considerably over the next few decades, owing to demographic shifts, population growth, urbanization, migration within and among countries, globalization, trade liberalization, and rapid expansion of middle classes in the developing world.