In 2007, for the first time in the history of the world, the numbers of people living in cities began to exceed those living in the countryside. As we live longer, we reduce birth rate. Most people move beyond child-bearing years and the median age of the population will increase substantially as well. Total human population of the Earth under these conditions will begin to level off significantly. We may reach 9 billion nevertheless as we move into mid 21st century, but that will be less than half the increase we might have expected had we kept increasing at the rate we are currently.
The additional two billion people we add by mid century will likely mostly live in cities. Thus, when we are 9 billion we should be about 5.3-5.4 billion (about 60 percent) in cities and about 3.7-3.8 billion (about 40 percent) living in the countryside. The mega-cities which reside on coastlines will be increasingly at risk due both to the anticipated elevation of sea level over the century and to the possibility of potentially violent storms as warming areas come to equilibrium with other parts of the planet. Thus, in excess of 10 percent of the population of cities may come under increased risk. Many of the at risk cities will need to construct special sea barriers, and may have special issues for obtaining potable water. These issues will need to be solved in a timely way or some of these cities may need to be abandoned by the 22nd century or before.
Cities are currently being forced to redesign or reinvent themselves. First, energy use per unit area is being reduced. Second, cities are also being redesigned to meet the needs of those who work within them or retire within them. Third, cities are moving to the edge with new technology, services and manufacture, and are doing this with an eye toward maximum efficiency. It’s not about saving jobs.
Rebuilding or adding to new construction in cities increasingly occurs upwardly rather than in outward sprawl. Lightly colored or white roofs reflect sunlight back into space and absorb little heat. Efficient construction with maximum insulation increasingly holds heat better in winter and keeps it out during the summer. Reducing inner space to about 500 sq. ft. per person maximizes efficiency and provides adequate living or working space. Passive solar heating may be utilized where it makes sense. Community gardens and markets increasingly meet the needs of those who live and work nearby. Underground transit, near or at ground level shopping, shops and kiosks increasingly meet needs. Underground water, sewer and garbage disposal are efficiently organized or reorganized to meet community needs.
Transportation within the city needs more effective redesign going forward, but these needs and strategies are being met efficiently and increasingly by cities. In the future we need a more effective intercity communication network so that many industries which provide end-stage products for use by city dwellers are at end-stage manufacturing centers at the cities edge which also contain reception points for products coming in from great distances or even from another city 20-50 miles distant. At that point movement of products from the cities outskirts to points all the way into the center of the city occurs efficiently. Within cities people live and work together in increasingly condensed centers as one moves inward toward the city center, but with a sense of a community living and working together effectively. Services are increasingly condensed at the city center. People can walk between them most of the time. Moving toward the outskirts of the city people are increasingly connected by people movers as they move away from lighter transportation systems.
Many variations on these themes may develop in time. As cities are increasingly powered by both heating and cooling systems based on solar, geothermal or other renewable energies. These systems can be highly efficient due to increasingly sophisticated energy-saving design systems that restrain air and water pollution, which should be at a minimum.