CLIMATE CHANGE THREATENS MORE THAN MEGASTORMS, FLOODS AND DROUGHTS. THE REAL PERIL MAY BE DISEASE
BY EUGENE LINDEN
Monday, Jul. 08, 1996
Floods. Droughts. Hurricanes. Twisters. Are all the bizarre weather extremes we've been having lately normal fluctuations in the planet's atmospheric systems? Or are they a precursor of the kind of climactic upheavals that can be expected from the global warming caused by the continued buildup of CO2 and the other so-called greenhouse gases? Scientists are still not sure. But one of the effects of the unusual stretch of weather over the past 15 years has been to alert researchers to a new and perhaps even more immediate threat of the warming trend: the rapid spread of disease-bearing bugs and pests.
Climate change, whether natural or man-made, may already be spreading disease and pestilence, according to a host of new studies, including a major report being prepared by the World Health Organization and other international institutions for release this summer. Malaria, for example, has been flourishing in recent years owing to unusually hot weather. Similarly, climate disruptions may be giving new life to such ancient scourges as yellow fever, meningitis and cholera, while fostering the spread of emerging diseases like hantavirus.
Underlying all these outbreaks is the same Darwinian mechanism: unusual weather such as dry spells in wet areas or torrential rains in normally dry spots tends to favor so-called opportunistic pests--rodents, insects, bacteria, protozoa, viruses--while making life more difficult for the predators that usually control them. Episodes of extreme weather are routinely followed by outbreaks of plagues, both old and new. Among the most recent examples:
CHOLERA. In 1991 a freighter coming from South Asia emptied its bilges off the coast of Peru. Along with the wastewater came a strain of cholera that found a home in huge algal blooms stimulated by unusually warm ocean waters and abundant pollution. The microbe then made its way into shellfish and humans. So far, the epidemic has infected over half a million people and killed at least 5,000.
HANTAVIRUS. In 1993 a six-year drought followed by heavy rains produced a tenfold increase in the population of deer mice in the American Southwest, leading to an outbreak of a deadly form of pulmonary hantavirus. The disease, which first appeared on a Navajo reservation, has since spread to 20 states and killed 45 people, nearly half of those infected.
PLAGUE. In 1994 a long monsoon in northern India followed by 90 consecutive days of 100[degrees]F heat drove rats into the cities. In Surat, they caused an outbreak of pneumonic plague. The ensuing panic killed 63 people and ultimately cost India $2 billion.
DENGUE FEVER. The coastal mountain ranges of Costa Rica had long confined dengue fever, a mosquito-borne disease accompanied by incapacitating bone pain, to the country's Pacific shore. But in 1995 rising temperatures allowed Aedes aegypti mosquitoes to breach the coastal barrier and invade the rest of the country. Dengue also advanced elsewhere in Latin America, reaching as far north as the Texas border. By September the epidemic had killed 4,000 of the 140,000 people infected.
Of all the infectious diseases humans will have to contend with as the world gets warmer, malaria 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 4 [degrees] F would more than double mosquito metabolism, forcing them to feed more often. A 4 [degrees] F rise in global temperatures could also expand malaria's domain from 42% to 60% of the planet. When temperatures rise above 104 [degrees] F, mosquitoes 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 sewage 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. Heat, increased ultraviolet radiation resulting from ozone depletion, and pollutants like chlorinated hydrocarbons all suppress the disease-battling immune systems--both for humans and for other animals. Epstein, who is one of the principal authors of the upcoming WHO study, notes that in recent years variants of the class of viruses that includes measles have killed seals in the North Sea, lions in the Serengeti and horses in Australia--three very different animals widely scattered around the globe.
A common denominator in each case: abnormal weather had caused malnutrition, weakened animal immune systems and spurred the reproduction of viruses. 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. "The message I take home," he says, "is that diseases afflicting plants and animals can send ripples through economies and societies no less disastrous than those affecting humans."
A small but persistent group of critics, many of them supported by the oil and coal industries, still don't buy it. S. Fred Singer, president of the industry-funded Science and Environment Policy Project, argues that Epstein and his colleagues fail to note the positive health benefits of warmer nights and winters. Others, like John Shlaes, executive director of the Global Climate Coalition, suggest that when the world is faced with the pressing health problems stemming from overcrowded cities and the collapse of sanitation systems, the threat of disease caused by climate change may seem like a minor concern.
No one disputes the role of poverty and overpopulation in spreading disease. That is no reason to ignore the warnings sounded by Epstein and his colleagues, however. Scientists first raised alarms about climate change in the late 1980s, but the international community has taken few concrete steps to address the problem. The world is gambling, in effect, that problems in the future will not be serious enough to warrant inconvenience in the present. With each passing year, the future gets closer and that bet gets bigger.