Many countries and groups are attempting to plan directly and rationally for sustainable development. All conditions of population work through human forms of social organization and technology to have an impact on the environment. Similarly, all conditions of the environment work through some form of human-social organization or technology to have an impact on the size or conditions of a population. The link between human wastes and health in a country, for example, will depend on the numbers of people, the type of wastes produced, the infrastructure for water procurement and waste disposal, and the infrastructure for health maintenance. It will also depend on the level of nutrition, and thus on the kind of food production a country has, as well as on world food prices. The ozone depletion that increases the incidence of eye disease and skin cancer in the southern hemisphere comes largely from past emissions of chlorofluorocarbons from the northern hemisphere.