John T. Houghton, author of Global Warming: The Complete Briefing (1997), believes that global warming will accelerate the spread of many diseases from the tropics to the middle latitudes. Mosquito-borne malaria (which already kills more than a million people a year in the tropics) could increase its present range, Houghton warned. "Other diseases which are likely to spread for the same reason are yellow fever, dengue fever, and... viral encephalitis," he wrote (Houghton, 1997, 132). After
1980, small outbreaks of locally transmitted malaria occurred in Texas, Georgia, Florida, Michigan, New Jersey, New York, and California, usually during hot, wet spells. Worldwide, according to Epstein, between 1.5 and 3 million die of malaria each year, mostly children. Mosquitoes and parasites that carry the disease have evolved immunities to many drugs.
According to Epstein, "If tropical weather is expanding it means that tropical diseases will expand. We're seeing malaria in Houston, Texas" (Glick, 1998). Epstein suggested that a resurgence of infectious disease might be a result of global warming. Warming may appear beneficial at first, Epstein said. Initially, some plants benefit from additional warmth and moisture, an earlier spring, and more carbon dioxide and nitrogen in the air. "But," he cautioned, "[w]arming and increased CO2 can also stimulate microbes and their carriers" (Epstein, 1998).
Since 1976, Epstein reported, thirty diseases have emerged which are new to medicine. Old ones, such as drug-resistant tuberculosis, have been given new life by new diseases (such as HIV/AIDS) that compromise the human immune system. By 1998, tuberculosis was claiming three million lives annually around the world. "Malaria, dengue, yellow fever, cholera, and a number of rodent-borne viruses are also appearing with increased frequency," Epstein reported (Epstein, 1998). During 1995, mortality from infectious diseases attributed to causes other than HIV/AIDS rose 22 percent above the levels of 15 years before in the United States. Adding deaths brought about by HIV/AIDS, deaths from infectious diseases have risen 58 percent in 15 years (Epstein, 1998). The IPCC included a chapter on public health in an update of its 1990 assessment which concluded, "[C]limate change is likely to have wideranging and mostly adverse impacts on human health, with significant loss of life" (Taubes, 1997).
Andrew Haines asserted, in Jeremy Leggett's Global Warming: The Greenpeace Report (1990),
Although winter bronchitis and pneumonia may be reduced [by global warming], it is quite likely that hay fever and perhaps asthma could increase. A combination of increases in temperature with increasing levels of tropospheric ozone could have clinically important effects, particularly in patients with asthma and chronic obstructive airways disease. (Haines, 1990, 154)
Epstein identified three tendencies in global climate change and related each to an environment that encourages infectious diseases. The three indicators are
(1) Increased air temperatures at high altitudes in the Southern Hemisphere;
(2) A rise in minimum (usually nighttime) temperatures that is greater than the rise in maximum (daytime) readings;
(3) An increase in extreme weather events, such as droughts and sudden heavy rains (Epstein, 1998).
"There is growing evidence for all three of these tell-tale 'fingerprints' of enhanced greenhouse warming," he said (Epstein, 1998).
A Sierra Club study indicated that a lengthy El Nino event during the middle 1990s provided an indication of how sensitive some diseases can be to changes in climate. This study cited evidence that warming waters in the Pacific Ocean contributed to a severe outbreak of cholera which led to thousands of deaths in Latin American countries during the 1990s. According to health experts quoted by the Sierra Club study, "[t]he current outbreak [of dengue fever], with its proximity to Texas, is at least a reminder of the risks that a warming climate might pose" (Sierra, 1999). The Sierra Club study concluded, "While it is difficult to prove that any particular outbreak was caused or exacerbated by global warming, such incidents provide a hint of what might occur as global warming escalates" (Sierra, 1999).
Willem Martens et al., writing in Climatic Change, attempted to sketch how a warmer, wetter climate would affect transmission of three diseases: malaria, schistosomiasis, and dengue fever. Martens and colleagues forecast that the size of areas affected by these diseases would expand with global warming. The diseases will expand north and south, as well as into higher mountains in the tropics. Martens and his colleagues expected that "[t]he increase in epidemic potential of malaria and dengue transmission may be estimated at 12 to 27 per cent and 31 to 47 per cent respectively" (Martens et al., 1997, 145). In contrast, they forecast that the transmission potential of schistosomiasis might decrease 11 to 17 percent.
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