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Gases in the atmosphere such as carbon dioxide and methane trap the sun's energy and warm the earth. This natural "greenhouse effect" is intensified by human activities, especially the combustion of fossil fuels such as coal, oil, and natural gas. Increased energy use in cars, homes, and factories raises the concentration of carbon dioxide in the atmosphere. The steady accumulation of these greenhouse gases can cause a variety of impacts on global climate. As the climate changes, natural systems may be destabilized, which could pose a number of risks to human health. In general, these risks affect whole populations rather than individuals or groups of people.
Exactly how much risk is posed to human health by climate change is difficult to quantify in terms of numbers of increased deaths or illnesses. For one thing, human populations differ in vulnerability. Factors such as crowding, food scarcity, poverty, and local environmental decline make populations in some developing countries especially vulnerable. Likewise, in industrialized countries, the demographic trend toward an aging population raises the health risks.
Climatic changes may have wide-ranging effects on human health, via both direct and indirect pathways. Direct health effects include increases in heat-related mortality and illness resulting from expected increases in the intensity and duration of heat waves (although temperature increases should also result in fewer cold-related deaths). Deaths, injuries, psychological disorders, and exposure to chemical pollutants in water supplies could increase if extreme weather events, such as storms and floods, become more frequent.
Indirect effects include increases in the potential transmission of vector-borne infectious diseases caused by the extensions of ranges and seasons of some vector organisms and acceleration of the maturation of certain infectious parasites. Some increases in non-vector-borne infectious diseases could occur (especially in tropical and subtropical regions) because of climate impacts on water distribution, temperature, and microorganism proliferation. Climate-induced changes in pollens and spores and temperature increases that enhance the formation and persistence of certain air pollutants could result in increases in respiratory illnesses. Though still uncertain, the regional effects of climate change on agricultural, animal, and fisheries productivity could increase the local prevalence of hunger and malnutrition (particularly in developing countries). Finally, sea level rise could result in physical and demographic disruptions, with consequences for public health.
Public health and medical professionals are focusing not only on the risks but also adaptive options to mitigate adverse impacts. Adaptive options to minimize health impacts include improved and extended medical care services; enhanced disaster preparedness and relief, increased use of protective technology (air conditioning, water purification, vaccination, etc.), public education directed at personal behaviors, and appropriate professional and research training. However, any technological adaptations such as use of pesticides to control disease-transmitting insects should also be assessed for potential health risks. In addition, improved and internationalize monitoring of health-risk indicators in relation to climate change are needed.
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