Lower world population by 20% by the end of the century.
ObstaclesThose who are worried about the need for a continually growing population to support growth will be the strongest opponents of any efforts to alter population dynamics. Thus, this topic is directly related to resolving the "lifestyle" issues discussed previously. Populations not as dependent on materialism will require lower influx into the work force. As populations become wealthier and as opportunities for women increase there is a natural decline in the birth rate. With only small changes in economic and social status population decline can be expected to occur if it is not deliberately opposed.
ImplementationRecent projections have made the risk of overpopulation even greater than previously thought. Some are now projecting a rise from 6.5 to 9 billion people by mid-21st century. This is not a sustainable level, if people are to have an adequate material existence and normal life span. As populations become more educated and women become emancipated the birth rate drops rapidly, usually within a generation. Thus, the most obvious steps to take concerning population increase have to do with improving the education and fiscal independence of women. The resistance of institutions dominated by men can be overcome by simultaneously improving the economic status of men so that they also feel that their lives will be comfortable without the need for large families to help support subsistence living. Steps mentioned previously that are concerned with keeping families from migrating to population centers will all be necessary to achieve this goal.
The issue of population needs to be treated separately for the developing and developed worlds. In the developed world several countries are already experiencing stable or declining population. Italy and Japan have birth rates below the replacement level. The US would have this as well if it wasn't for the high rate of immigration. For these societies they are most concerned with not having a large enough work force. They have no credible plans on what to do about this because of the blinders that exist when only a consumerist/capitalist/growth model is considered. A lower level of consumerism and a transition to a sustainable society would require less material resources and would allow for more economic activity to be taken up with serving human needs.
For the developing world the first step is to cut the birth rate of the poorest by more emphasis on programs that work. These include micro-credit, education for women, and insulation from global forces which cause subsistence farming to fail. In India, for example, 150,000 farmers have committed suicide over the last decade as they fell into unrecoverable debt. Making farming more "efficient" by use of patented crops and chemical fertilizers ignores the social costs to the rural communities and also ignores the ecological impact from the higher energy use such farming requires.
The emerging middle and upper classes in the "BRIC" countries (Brazil, Russia, India, China) will tend to have smaller families, but they will also cause a rise in economic inequality. As these groups will also wield the most economic and political power they can be expected to support policies which favor the own parochial interests. This will cause a neglect of policies to support the poor and thus cause a worsening of population control efforts. Since all these countries have fairly strong central governments it is possible to create a more foresighted social policy if the leadership wishes to make this a priority. China has taken the lead here in the past, but it is not clear if they will continue to promote a strict policy in the future. India is currently a disaster and will soon exceed China in total population. There seems to be no real effort in this direction currently.
To produce an actual decline in population below current levels by the end of the century will require that many more countries transition to the social expectations of Italy and Japan. This means more economic security and less of a need to be supported by one's children in old age. It also means that social norms about the need for early (or any) marriage will have to be reconsidered. People can take pleasure from other forms of social interactions if societies consider this as acceptable. More emphasis on personal development and accomplishments, especially for women, can replace the idea that one only lives through one's children. There are three generations between now and then. Social norms have changed before over such a period of time, so it is not impossible for this to happen.