Environmental hazards comprise a significant portion of the health risks facing the poor. By one estimate, environmental causes account for 21 percent of the overall burden of disease worldwide (the combination of days spent sick and deaths due to sickness) (WHO 2002 in Cairncross et al. 2003:2). Acute respiratory infections and diarrhea rank among the highest contributors to the disease burden in the developing world, and these are mostly diseases of the poor (WHO 2002:83).

A disproportionate share of environmental health risk is borne by the very young. Although children under five constitute just 10 percent of the world’s population, they suffer 40 percent of the environment-related burden of disease. Diarrhea, caused by unclean water and inadequate sanitation, is responsible for the deaths of an estimated 1.8 million people worldwide each year, 1.6 million of which are children under five (Gordon et al. 2004:14).

Respiratory ailments are caused in large part from exposure to high levels of indoor smoke from cooking with dung, wood, or other biomass fuels. More than half the world’s population— 3.5 billion people—currently depend on such fuels as their main energy source (Desai 2004:vii). Analysis by the International Energy Agency shows that this dependence will likely increase in the years ahead, with an additional 200 million people—most of them poor—relying on these fuels by 2030 (IEA 2002:30).

Indoor air pollution is linked to over 1.6 million deaths a year, 500,000 of them in India alone. More than half of those who die of respiratory infections related to indoor air pollution are children under the age of five (Warwick and Doig 2003:2). In urban areas, ambient air pollution from auto exhaust, industrial smoke stacks, dust, and other particulates is also a significant health risk. Ambient air pollution causes some 800,000 deaths a year, most of them in the developing world (WHO 2002:69).

Looking to the future, climate change comprises a considerable environmental health risk, since it can intensify existing environmental health threats. Vector-borne diseases such as malaria, dengue fever, schistosomiasis, and Chagas disease could expand their ranges as temperature and rainfall patterns change. Mosquitoes are among the first organisms to expand their range when climate conditions become favorable, so cases of malaria and dengue fever may increase their already heavy toll among the poor (WRI et al.1998:70). Diarrheal organisms are also sensitive to changes in temperature and humidity, with the health risk they pose increasing as average temperatures rise. A study in Peru found that hospital admissions for diarrhea increased as much as 12 percent for every 1 degree C increase in temperature (McMichael et al. 2003:215). On a broader scale, the World Health Organization estimates that in 2000, climate change was responsible for 2.4 percent of all cases of diarrhea and 2 percent of all cases of malaria worldwide (WHO 2002:72).