Of all the infectious diseases humans will have to contend with as the world gets warmer may be the worst. Malaria is already the world's most widespread mosquito-borne illness. Rising temperatures will not only expand the range of Anopheles mosquitoes, but make them more active biters as well. Paul Epstein, an epidemiologist with the Harvard School of Public Health , notes that a temperature rise of 2 C would more than double mosquito metabolism, forcing them more often. When temperatures rise above 40 C, mosquitos begin to die off-but at those temperatures, so do people and the crops on which they live.
Humans often make matters worse for themselves by the changes they make in their local environments.
Unusually warm waters played an important role in the cholera epidemic that hit Latin America in 1991, but the outbreak was also exacerbated by seawage poured into the waters off Asia and Latin America, the destruction of pollution-filtering mangroves in the Bay of Bengal and overcrowding in the cities. The same synergies that empower microbes also weaken our defenses against them. Epstein also notes that once ordinarily benign microbes invade weakened animals, they can become sufficiently deadly to invade healthy populations. The real threat for people, says Epstein, may not be a single disease , but armies of emergent microbes raising havoc among a host of creatures. A small but persistent group of critics, many of them supported by the oil and coal industries, still don't buy it.