As the number of urban consumers and their material expectations rise and as the use of fossil fuels increases, cities contribute to the large-scale pressures on the biosphere including climate change. These include exposure to lead, air pollution, traffic hazards, and the 'urban heat island' amplification of heatwaves. Beyond the traditional risks of diarrhoeal disease and respiratory infections in the urban poor and the adaptation of various vector-borne infections to urbanization, the urban environment poses various physicochemical hazards. In many low-income countries, this process is being slowed by the pressures and priorities of economic globalization. This occurred in response to environmental blight, increasing literacy, the development of democratic government, and the collective accrual of wealth. The early industrializing period of unplanned growth and laissez-faire economic activity in cities in industrialized countries has been superseded by the rise of collective management of the urban environment. Urban populations have long been incubators and gateways for infectious diseases. However, they are also sources of poverty, inequality, and health hazards from the environment. Cities are sources of creativity and technology, and they are the engines for economic growth. Cities have multiplied and expanded rapidly worldwide over the past two centuries.

Urban living is the keystone of modern human ecology.

The globalization of cities leads to