Cities — Global Population Shrinkage And Economic Growth
Proviso: If climate change shifts from gradual to "abrupt" during the next 20 years, that bad news will obliterate the good news I otherwise expect in the realms of global population shrinkage and economic growth.
Cities have always been wealth creators. Cities have always been population sinks. This year, 2007, is the crossover point from a world predominantly rural to a world predominantly urban.
The rate of urbanization is currently about 1.3 million new city dwellers a week, 70 million a year, still apparently accelerating. The world was 3% urban in 1800, 14% urban in 1900, 50% urban this year, and probably headed in the next few decades to around 80% urban, which has been the stabilization point for developed countries since the mid-20th-century.
Almost all the rush to the cities is occurring in the developing world (though the countryside continues to empty out in developed nations). The developing world is where the greatest poverty is, and where the highest birthrates have driven world population past 6.5 billion.
Hence my optimism. Cities cure poverty. Cities also drive birthrates down almost the instant people move to town. Women liberated by the move to a city drop their birthrate right on through the replacement rate of 2.1 children/woman. No one expected this, but that's how it worked out. As a result, there will be another billion or two people in the world total by midcentury, but then the total will head down--- perhaps rapidly enough to be a problem, as it already is in Russia and Japan.
Poverty in the megacities (over 10 million) and hypercities (over 20 million) of the developing world will be highly visible as the disaster it is. (It was worse out in the bush, only not as visible there. That's why people leave.) But the poor who were trapped in rural poverty create their own opportunity once they're in town by creating their own cities--- the "squatter cities" where one billion people now live. They recapitulate the creation of cities past by generating a seething informal economy in which everyone works. The dense slums, if they don't get bulldozed, eventually become part of the city proper and part of the formal economy. It takes decades.
Globalization and urbanization accentuate each other. Medical care that couldn't reach the villages can reach slum dwellers. The newly liberated women in the slums create and lead CBOs (community based organizations, some linked with national and global NGOs) to handle everything from child care to micro-finance. If the city has some multinational corporations closely surveiled by do-gooders back home, their pay rates and work conditions will raise the standard throughout the city.
The sudden urbanization is a grassroots phenomenon, driven by the resourcefulness and ambition of billions of poor people busy getting out of poverty as fast as they can. Some nations help the process (China is exemplary), some hinder it (Zimbabwe is exemplary), none can stop it.