Human population size, environment, and health

The number of people has increased in a series of steps by around five orders of magnitude over the past 100 000 years as geographical dispersal and cultural changes expanded access to food and other resources. The last 10-fold increase has occurred in just over two centuries.

The main components of the complex relationship between environment and population size are: (1) the supply of environmental resources limits population size; (2) human societies typically extend that limit via cultural and technical developments; and (3) such extensions often cause depletion and degradation of the natural environment.

Historical perspective

Until the 19th century, all agrarian-based societies had both high death rates and high birth rates. Human populations have greatly increased pressures on the natural environment over the past two centuries by (1) expansion of numbers, and (2) increased material and energy intensities of productive activities. Initially, most environmental degradation was localized, such as urban-industrial air pollution, chemical pollution of waterways, and urban filth.

The situation today

Environmental damage is more extensive, systemic and cumulative—and the longer-term consequences for health are potentially much more serious. Global climate change is a prominent example of systemic overloading of the biosphere. Data on large-scale processes indicate that environmental resources and services are currently being used up at approximately 130% of the sustainable rate. This weakening of global life-supporting processes poses long-term risks to human health.

The future

Living within the environmental constraints will require radical changes in consciousness and institutional reconfigurations in both high- and low-income countries. A useful historical analogy lies in the radical and wide-ranging changes required between the mid 19th and early 20th centuries to render urban life in economically advanced countries compatible with child survival. High-income countries now generally enjoy high levels of health, but sustaining this historically remarkable level of population health will depend increasingly on achieving a secure world, and this in turn will require generalizing of health gains to the total human population. This will require the effective control of births, also a redefinition of ‘progress’ and the way we measure it, so that the interests of future generations are safeguarded. Physicians are well placed, individually and collectively, to foster public understanding of why large-scale environmental disruption jeopardizes the health of future generations and why it is in all our interests to avert this threat.