The drivers of change

Environmental change and its attendant health impacts are driven by many factors, including economic growth, population growth and movements, urbanization, transportation, and war, to name just a few. Here we focus on three broad trends – the intensification of agriculture, industrialization, and rising energy use – which stand out in terms of their profound impacts on the physical environment and their enormous potential for influencing human health. Given current development patterns, all are essential for economic development and improved welfare. Yet, all lead to pressures on the environment, such as pollutant emissions and resource depletion, that in turn can increase human exposure to threats in the environment.

Intensification of agriculture is essential for producing more food but, when not well managed, creates substantial risks, such as exposing workers and communities to toxic pesticides, contaminating groundwater supplies, and creating pesticide-resistant pests. Land clearing, irrigation, and dams can bring increases in vector-borne diseases such as malaria and schistosomiasis, both of which exact a huge toll in rural areas of the developing world.

Industrialization is the linchpin of economic growth and, like urbanization to which it is closely related, is associated with major gains in health. Yet, along with rising standards of living – at least for a majority of the population – industrialization often means increased exposure to heavy metals, persistent chemicals such as polychlorinated biphenyls (PCBs), and other toxic chemicals. This is especially true for workers and the poor who often live close to factories. Such exposures are likely to be increasingly pronounced in the developing world, where the most rapid industrialization is occurring.

Rising energy use is needed to fuel industrial growth but brings many attendant problems. Local air pollution from industrial and vehicle emissions has proved difficult to manage even in developed economies. Fossil fuel use also has the potential to alter the Earth’s climate, with a predicted range of health impacts from severe storms, to drought, to flooding, to an increase in insect-borne diseases such as malaria. Energy demand, which is already huge in the developed countries, is rising fastest in the developing world.

Although these trends are discussed separately here, in the real world they rarely occur in isolation. Rising energy use, for instance, is part and parcel of industrialization and agriculture. The effects of industrialization are often difficult to disentangle from those of urbanization. Many of the effects of these trends are well known and predictable (for example, increased air pollution that accompanies rising use of fossil fuels, or exposure to toxic chemicals through improper disposal of industrial wastes). Others, however, are far less certain, though potentially large, such as those associated with global climate change and wide-scale ecological disruption.

Until recently, discussions of environmental threats to health have tended to focus on direct toxicological effects of specific insults or exposures. Now, awareness is growing that changes in the environment can affect health in indirect and often unexpected ways as well, by disrupting local or global ecosystems [16]. For instance, soil erosion stemming from poor agricultural practices can result in reduced crop yields; this could have important consequences for nutrition. Farm animal wastes in the eastern United States are suspected of causing toxic algal blooms, leading to massive fish kills and potential harm to humans [17]. Even well-intended development projects can have unexpected outcomes, as occurred in Africa’s Senegal River Valley, where the construction of two dams set off a cascade of events that ultimately contributed to nutritional problems for the population and a dramatic increase in schistosomiasis. (See Regional Profile on Damming the Senegal River.)

Although agricultural intensification, industrialization, and rising energy use hold considerable potential for harming both the environment and public health, these negative impacts are by no means inevitable. Experience has shown that it is possible to manage economic growth in ways that preserve environmental quality and enhance human health. But this will not come from the random interaction of market forces alone [18]. Achieving the benefits of economic development while minimizing its deleterious impacts will require an increased awareness of links between environment and health and a broader approach to strategies to improve public health.

In particular, achieving these benefits will depend on a greater emphasis on prevention, either by managing the environment so that health risks do not occur, or by intervening before these risks lead to illness. Prevention is essential because the health risks associated with environmental degradation and change – such as the impacts of increasing fossil fuel use or the lack of sanitation in burgeoning slums – are simply too big for the health sector to tackle alone. Typically, health strategies focus on individual cases, attempting to prevent a person from contracting a disease and, when that is not possible, treating the disease. Although such approaches have been enormously successful in improving public health, it is clearly possible to do even more by pursuing strategies that intervene earlier in the pathway toward illness.

Environmental interventions seek to do that by preventing exposure to the pathogens that cause disease or eliminating conditions that enable vectors to breed. For instance, rather than just treating diarrhea with oral rehydration therapy, which saves lives but does not reduce the incidence of the disease and the suffering it causes, an environmentally based approach would seek to increase access to water and sanitation and hygiene education.

In the past few years, several organizations have called for broadening health strategies by factoring in environmental considerations as well [19]. In a recent report for instance, WHO made the case for pursuing “upstream” policy actions – in other words, actions removed from the immediate hazards that instead address the underlying pressure or driving force [20]. Health improvements from upstream interventions, such as the provision of water and sanitation or a shift away from fossil fuel use, may be slower in coming than improvements from clinical intervention, notes WHO. For this reason, environmental approaches must be combined with clinical strategies to treat immediate health problems. But in the long run, the benefits of prevention are more enduring in terms of improved public health, a cleaner and safer environment, and stronger socioeconomic development.

A key challenge of this approach is that it requires coordination among many sectors – for instance, environment, energy, transportation, and health – that often don’t interact. But on the positive side, the benefits will reach far beyond the health sector as well. An increased emphasis on public transportation versus the private car will reduce air pollution and associated respiratory illnesses. But such a shift might not be justified on the basis of health improvements alone. However, when the potential economic savings from reduced urban congestion are factored in, not to mention reduced pollution damage to regional ecosystems, the case becomes more compelling.

Improving both health and the environment will also require increased consideration of equity issues, or how risks are distributed among populations. All too often, as the following chapters document, environmental risks are borne disproportionately by the poor and disenfranchised – not just in developing countries but in affluent nations as well. This issue warrants increased attention because economic disparities are increasing both within and among countries. One consequence of these disparities is that the rich can often protect themselves from environmental threats to health, while the poor usually cannot.

16. A.J. McMichael, Planetary Overload: Global Environmental Change and the Health of the Human Species (Cambridge University Press, Cambridge, U.K., 1993).

17. Joby Warrick and Todd Shields, “Maryland Counties Awash in Pollution-Causing Nutrients Reports Suggest State Faces Battle Controlling Agricultural Runoff into the Bay,” The Washington Post (October 3, 1997), p. A1.

18. David Bradley, “Health, Environment, and Tropical Development,” Health and the Environment: The Linacre Lectures, Bryan Cartledge, ed. (Oxford University Press, Oxford, U.K.,1994), p. 147.

19. See World Health Organization (WHO), Health and Environment in Sustainable Development: Five Years After the Earth Summit (WHO, Geneva, 1997) and Helen Murphy, Bonnie Stanton, and Jennifer Galbraith, “Prevention: Environmental Health Interventions to Sustain Child Survival,” Applied Study No. 3 (Environmental Health Project, Washington, D.C., 1997).

20. World Health Organization (WHO), Health and Environment in Sustainable Development: Five Years After the Earth Summit (WHO, Geneva, 1997), p. 1.