Climate Change and Human Health
Climate change and human health (Encyclopedia of Environmental Issues, Revised Edition)
Direct deaths from extremely cold or warm weather (hypothermia, heatstroke) are relatively rare in developed countries, but occasionally large numbers of people are killed or otherwise seriously affected by heart attacks caused by the weather (including people trying to shovel too much snow at once). The global warming that has occurred over the past century, and is generally expected to continue, can affect the number of deaths related to weather—reducing the number harmed by severe cold but increasing the number harmed by extreme heat. Climate changes can also alter the numbers of people affected by flood and drought as well as the ranges of parasites and disease vectors.
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Direct Effects (Encyclopedia of Environmental Issues, Revised Edition)
Warmer temperatures tend to lead to more frequent deaths from excessive heat, although this is mitigated in the case of greenhouse gas warming by the fact that the greatest warming occurs at night and thus in winter (and especially in the Arctic and Antarctic regions), when the temperatures otherwise would be cooler. Warmer temperatures also reduce the numbers of deaths associated with extreme cold (including cardiovascular and pulmonary diseases, such as influenza). There are actually more deaths from cold than from heat in many areas that face both threats. In Europe, estimated annual deaths amount to approximately 1.5 million from cold compared to about 200,000 from heat; the warmer United States suffered twice as many deaths from cold as from heat from 1979 through 1997. Even the severe heat wave of August, 2003, which led to an estimated 35,000 deaths in Europe (nearly half in France, partly because most doctors who practiced there were away on vacation at the time), resulted in only a modest increase in the number of deaths that year from excessive heat.
Climate change can also alter rainfall patterns, causing some areas to be more subject to floods (which inflict heavy damage and can also lead indirectly to other health problems) or droughts (which can lead to crop failures and water shortages). Scientists do not yet know, however, whether the trend toward warming will result in more floods, more droughts, or even both....
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Food and Water (Encyclopedia of Environmental Issues, Revised Edition)
Climate changes can also affect food crops. Judging from the past experience of the Medieval Warm Period, this can lead to greater production in some places (partly from longer growing seasons as well as the fertilizing effect of increased carbon dioxide) and shortages in others (caused by droughts and floods rather than the temperature changes, though this can change what crops are grown in particular areas). These shortages can lead to malnutrition, including deficiency diseases, or even famine in poor countries.
Drought also makes obtaining water supplies more difficult even as a population continues to grow. One consequence is that people are often forced to work hard (expending labor that would otherwise be available for other needs) for water that is often tainted, which leads to increasing outbreaks of diseases such as dysentery, typhoid fever, and cholera, as well as aquatic parasites such as guinea worms. When water is scarce, cleaning and other sanitation practices suffer. Unclean bodies (especially hands) help spread diseases, and unclean clothes can carry and spread parasites such as lice.
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Diseases (Encyclopedia of Environmental Issues, Revised Edition)
Climate changes can affect the ranges of various life-forms in many ways. Warmer weather, particularly if it is also wetter, tends to increase the numbers of insects; the mild winters created by greenhouse gas warming are especially important for those insects that are susceptible to freezing temperatures. Many of these are disease vectors, spreading serious diseases such as malaria, dengue fever, yellow fever, typhus, and the plague. Not only may these insects cover larger areas (and also spread to higher elevations, as shown by a 1997 malaria outbreak in Papua New Guinea at an altitude of 2,100 meters, or 6,900 feet), but warmer temperatures can also enable them to be active for a longer portion of the year. This is especially crucial for mosquitoes that carry dengue fever, but malaria exposure may also increase. Although most malaria victims survive, the disease is very persistent, with frequent relapses, and thus very debilitating. On the other hand, it is estimated that warming will reduce the incidence of schistosomiasis, and possibly also the range of ticks that carry diseases such as Rocky Mountain spotted fever.
In areas that become significantly wetter, increased molds can lead to increases in hay fever and asthma, which can be fatal. Flooding can drive rodents, which help spread diseases such as the plague, from their burrows. When carbon dioxide increases, crop yields improve, but so does the growth of allergenic pollens...
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Further Reading (Encyclopedia of Environmental Issues, Revised Edition)
Braasch, Gary. Earth Under Fire: How Global Warming Is Changing the World. Updated ed. Berkeley: University of California Press, 2009.
Fagan, Brian. The Great Warming: Climate Change and the Rise and Fall of Civilizations. New York: Bloomsbury, 2008.
Johansen, Bruce E. The Global Warming Desk Reference. Westport, Conn.: Greenwood Press, 2002.
Lomborg, Bjørn. Cool It: The Skeptical Environmentalist’s Guide to Global Warming. New York: Alfred A. Knopf, 2007.
Mann, Michael E., and Lee R. Kump. Dire Predictions: Understanding Global Warming. New York: DK, 2008.
Michaels, Patrick J., and Robert C. Balling, Jr. Climate of Extremes: Global Warming Science They Don’t Want You to Know. Washington, D.C.: Cato Institute, 2009.
Rosenberg, Tina. “The Burden of Thirst.” National Geographic, April, 2010, 99-115.
Singer, S. Fred, and Dennis T. Avery. Unstoppable Global Warming: Every 1,500 Years. Updated ed. Lanham, Md.: Rowman & Littlefield, 2008.
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Climate Change and Human Health (Encyclopedia of Public Health)
Human societies over the ages have depleted natural resources and degraded their local environments. Populations have also modified their local climates by cutting down trees or building cities. It is now apparent that human activities are perturbing the climate system at the global scale. Climate change is likely to have wide-ranging and potentially serious health consequences. Some health impacts will result from direct-acting effects (e.g., heatwave-related deaths, weather disasters); others will result from disturbances to complex ecological processes (e.g., changes in patterns of infectious disease, in freshwater supplies, and in food production).
WHAT IS CLIMATE CHANGE?
Global climate change is caused by the accumulation of greenhouse gases in the lower atmosphere. The global concentration of these gases is increasing, mainly due to human activities, such as the combustion of fossil fuels (which release carbon dioxide) and deforestation (because forests remove carbon from the atmosphere). The atmospheric concentration of carbon dioxide, the main greenhouse gas, has increased by 30 percent since preindustrial times.
Projections of future climate change are derived from global climate model or general circulation model (GCM) experiments. Climatologists of the Intergovernmental Panel on Climate Change (IPCC) review the results of these experiments for global and regional assessments. It is estimated that global mean surface temperature will rise by 1.5° to 3.5° C by 2100. This rate of warming is significant. Large changes in precipitation, both increases and decreases, are forecast, largely in the tropics. Climate change is very likely to affect the frequency and intensity of weather events, such as storms and floods, around the world. Climate change will also cause sea level rise due to the thermal expansion of the oceans and the melting of the mountain glaciers. Global mean sea level is anticipated to rise by 15 to 95 centimeters by 2100. Sea level rise will increase vulnerability to coastal flooding and storm surges. The faster the climate change, the greater will be the risk of damage to the environment. Climatic zones (and thus ecosystems and agricultural zones) could shift toward the poles by 150 to 550 kilometers by 2100. Many ecosystems may decline or fragment, and individual species may become extinct. The IPCC Second Assessment report concludes that climate change has probably already begun.
IMPACTS ON HEALTH
To assess the potential impacts of climate change on health, it is necessary to consider both the sensitivity and vulnerability of populations for specific health outcomes to changes in temperature, rainfall, humidity, storminess, and so on. Vulnerability is a function both of the changes to exposure in climate and of the ability to adapt to that exposure (see Figure 1).
Science classically operates empirically, via observation, interpretation, and replication. However, having initiated a global experiment, it would not be advisable to wait decades for sufficient empirical evidence to describe the health consequences. Risk assessment must therefore be carried out in relation to future environmental scenarios. The traditional "top-down" approach is to
answer the question, "If climate changes like scenario X, then what will be the effect on specific health outcomes?" In contrast, "bottom-up" approaches begin with the question, "How much climate change can be tolerated?"
It is important to distinguish between "climate and health" relationships and "weather and health" relationships. Climate variability occurs on many time scales. Weather events occur at daily time scale and are associated with many health impacts (e.g., heatwaves and floods). Climate variability at other time scales also affects health. In particular, the El Niño Southern Oscillation has been shown to influence interannual variability in malaria, dengue, and other mosquito-borne diseases. Climate change is the long-term change in the average weather conditions for a particular location. Climate change will become apparent as a change in annual, seasonal, or monthly means. Thus, incremental climate change will be superimposed upon the natural variability of climate in time and space.
Natural Disasters. Climate change will increase the risk of both floods and droughts. Ninety percent of disaster victims worldwide live in developing countries, where poverty and population pressures force growing numbers of people to live in harm's wayn flood plains and on unstable hillsides. Unsafe buildings compound the risks. The vulnerability of those living in risk-prone areas is perhaps the single most important cause of disaster casualties and damage.
Water Quality and Quantity. Human health depends on an adequate supply of potable water. By reducing fresh water supplies, climate change may affect sanitation and lower the efficiency of local sewer systems, leading to increased concentrations of pathogens in raw water supplies. Climate change may also reduce the water available for drinking and washing. In developed countries, the anticipated increase in extreme rainfall events, which may be associated with the outbreaks of diarrheal diseases, may overwhelm the public water supply system. Flooding is likely to become more frequent with climate change and can affect health through the spread of disease. In vulnerable regions, the concentration of risks with both food and water insecurity can make the impact of even minor weather extremes (floods, droughts) severe for the households affected. The only way to reduce vulnerability is to build the infrastructure to remove solid waste and waste water and supply potable water. No sanitation technology is "safe" when covered by flood waters, as fecal matter mixes with flood waters and is spread wherever the flood waters go.
Food Security. Current assessments of the impact of climate change indicate that some regions are likely to benefit from increased agricultural productivity while others may suffer reductions, according to their location and dependence on the agricultural sector. The IPCC has reviewed the results of many modeling experiments that project future changes in crop yields under climate change. Climate change may increase yields of cereal grains at high and midlatitudes but may decrease yields at lower latitudes. The world's food system may be able to accommodate such regional variations at the global level, with production levels, prices, and the risk of hunger being relatively unaffected by the additional stress of climate change. However, populations in isolated areas with poor access to markets may still be vulnerable to locally important decreases or disruptions in food supply.
Heat Waves and Milder Winters. Heat stress is a direct result of exposure to high temperatures. Stressful hot weather episodes (heat waves) cause deaths in the elderly, as well as heat related illnesses such as heat stroke and heat exhaustion. A change in world climate, including an increase in the frequency and severity of heat waves, would affect the quality of life in many urban centers. Heat waves are responsible for a significant proportion of disease-related mortality in developed counties such as the United States and Australia, where the impact of weather disasters has been significantly reduced. Milder winters under climate change would reduce the excess morbidity and mortality, such as the United Kingdom, the beneficial impact may outweigh the detrimental.
Air Pollution. The air is full of particles and gases that may affect human health, such as pollen, fungal spores, and pollutants from fossil fuel emissions. Weather conditions influence air pollution via pollutant (or pollutant precursor) transport and/or formation. Exposures to air pollutants have serious public health consequences. Climate change, by changing pollen production, may affect timing and duration of seasonal allergies.
Social Dislocation. The growth in the number of refugees and displaced persons has increased markedly. Refugees represent a very vulnerable population with significant health problems. Large-scale migration is likely in response to flooding, drought, and other natural disasters. Both the local ecological disturbance caused by the extreme event and the circumstances of population displacement and resettlement would affect the risk of infectious disease outbreaks. Even displacement due to long-term cumulative environmental deterioration, including sea level rise, is associated with such health impacts.
Infectious Diseases. Vector-borne diseases are transmitted by insects (e.g., mosquitoes) and ticks that are sensitive to temperature, humidity, and rainfall. Climate change may alter the distribution of important vector species, and this may increase the risk of introducing disease into new areas. Temperature can also influence the reproduction and survival of the infective agent within the vector, thereby further influencing disease transmission in areas where the vector is already present. However, the ecology and transmission dynamics of vector-borne diseases are complex. The climate factors that could critically influence transmission need to be identified before the potential impact of a changing climate can be assessed.
Malaria is on the increase in the world at large, but particularly in Africa. In several locations around the world, malaria is reported in the twenty-first century at higher altitudes than in preceding decades, such as on the mountain plateaus in Kenya. The reason for such increases has not yet been confirmed but include population movement and the breakdown in control measures. Climate change may contribute to the spread of this major disease in the future in highlands and other vulnerable areas. Climate change impact models suggest that the largest changes in the potential for disease transmission will occur at the fringesn terms of both latitude and altitudef the potential malaria risk areas. The season transmission and distribution of many diseases that are transmitted by mosquitoes (dengue, yellow fever), sandflies (leishmaniasis), and ticks (Lyme disease, tick-borne encephalitis) may also be increased or decreased by climate change.
ADAPTATION AND MITIGATION
There are two responses to global climate change:
- Mitigation. Intervention or policies to reduce the emissions or enhance the sinks of greenhouse gases. The current international legal mechanism for countries to reduce their emissions is the United Nations Framework Convention on Climate Change (UNFCCC).
- Adaption. Responses to the changing climate (e.g., acclimatization in humans) and policies to minimize the predicted impacts of climate change (e.g., building better coastal defenses).
The key determinants of healths well as the solutionsie primarily outside the direct control of the health sector. They are rooted in areas such as sanitation and water supply, education, agriculture, trade, transport, development and housing. Unless these issues are addressed, it can be difficult to make improvements in population health and reduce vulnerability to the health impacts of climate change.
R. SARI KOVATS
(SEE ALSO: Environmental Determinants of Health; Geography of Disease)
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McMichael, A. J., and Haines, A. (1997). "Global Climate Change: The Potential Effects on Health." British Medical Journal 315:80509.
Patz, J. A.; McGeehin, M. A.; Bernard, S. M.; Ebi, K. L.; Epstein, P. R.; Grambsch, A.; Gubler, D. J.; and Reiter, P. (2000). "The Potential Health Impacts of Climate Variability and Change for the United States: Executive Summary of the Report of the Health Sector of the United States National Assessment." Environmental Health Perspectives 108:36776.
Watson, R.; Zinyowera, M. C.; Moss, R. H.; and Dokken, D., eds. (1996). "Climate Change 1995. Impacts, Adaptations, and Mitigation of Climate Change: Scientific and Technical Analyses." Second Assessment Report of the Intergovernmental Panel on Climate Change. Cambridge: Cambridge University Press.