In contemporary low-income settlements, local environmental problems are a major cause of disease and death whilst contributions to global environmental degradation remain small. Inadequate household water and sanitation, smoky cooking fuels, waste accumulation in the neighbourhood, disease-carrying pests all are major contributors to ill-health and mortality, especially among children, and all involve closely interrelated local environmental processes. Virtually everyone living, working and socialising in the neighbourhood is at risk but especially women and children. Low-income settlements may also come to be the worst affected by global environmental damage but they have immediate concerns that are, and ought to be, the priority for local action.
In contemporary affluent settlements, the most serious local environmental hazards have been displaced or reduced, while existing lifestyles pose major, if often uncertain, delayed and diffuse threats to human life support systems. Waste, once a problem primarily in and around peoples homes and workplaces, now interferes with a range of regional and even global processes. Global sustainability is challenged by high levels of materials and energy consumption and waste generation, selective pressures on distant ecosystems, new hazards arising from technologies developed to meet the demands of the affluent. And just as it is hard to live in a deprived neighborhood in a Southern city and avoid the local environmental hazards, so it is hard to live in an affluent neighborhood in the North and avoid contributing to global environmental burdens.
Between these two extremes are a range of city-wide and regional problems that tend to be most severe in large, industrializing middle-income cities. Pollution of ambient urban air and waterways are typical examples. They reflect increasing levels of polluting activities, involving especially industries, transport and energy conversion, along with the displacement of sewerage and waste burdens from the neighborhood to the city levels. In cross-country studies, this class of problems has received the most attention, generating the notion of the environmental Kuznets curve: an inverted U displaying the rise and then decline of environmental burdens with increasing wealth.
It would be a serious mistake to interpret this transition as a set of stages through which a city inevitably passes. Most notably:
- The global commons are being depleted and the historic transition cannot provide a model for future urban development.
- Good governance, as well as fortunate geography, can reduce all levels of environmental burden
- Inter-scale effects enable multiple burdens to be addressed simultaneously.
- Intra-urban differences can be just as significant as inter-urban differences.
- Rural-urban links are more significant than this simplified transition allows there is considerable overlapping of urban environmental burdens, and problems such as ambient air pollution affect a wide range of cities.