Nature Running Wild!

Atmospheric changes impact the environment in dramatic ways such as flooding. July 17, 2000

As the atmosphere heats up, the risks to human health pop up like a mosquito-borne virus. From the West Nile virus that found its way to New York last year to an epidemic of cholera, malaria and Rift Valley fever spawned by flooding in the Horn of Africa, the evidence of global warming on human health is everywhere, according to Paul Epstein, associate director of the Center for Health and the Global Environment at Harvard Medical School.

"Global warming can also threaten human well-being profoundly, if somewhat less directly, by revising weather patterns, particularly by pumping up the frequency and intensity of floods and droughts and by causing rapid swings in the weather, Epstein noted in this month's issue of Scientific American.

"As the atmosphere has warmed over the past century, droughts in arid areas have persisted longer, and massive bursts of precipitation have become more common. Aside from causing death by drowning or starvation, these disasters promote by various means the emergence, resurgence and spread of infectious diseases."

"That prospect is deeply troubling, because infectious illness is a genie that can be very hard to put back into its bottle," Epstein added. "It may kill fewer people in one fell swoop than a raging flood or an extended drought, but once it takes root in a community, it often difies eradication and can invade other areas."

Developing countries territories that are especially susceptible to infectious disease -- don't have the money or technology to prevent or cure outbreaks. This shortfall has serious implications for the rest of the world, Epstein said.

"In these days of international commerce and travel, an infectious disorder that appears in one part of the world can quickly become a problem continents away if the disease-causing agent, or pathogen, finds itself in a hospitable environment," Epstein noted. Case in point: the West Nile virus, which showed up for the first time in North America last year.

Epstein points to three severe weather events triggered by global warming -- floods, droughts and heat waves -- that bring with them infectious diseases usually carried by blood-sucking, heat-loving mosquitoes.

Mosquito-borne diseases are expected to increase because the agents are extremely sensitive to meteorological conditions. Diseases such as malaria, dengue fever, yellow fever and several types of encephalitis are sounding the loudest alarms -- alarms heard all over the world.

Global warming has the potential to exacerbate water-borne diseases, including cholera, which causes severe diarrhea. Drought enhances water-borne diseases by wiping out supplies of safe drinking water and concentrating contaminants that might otherwise remain dilute.

"Further, the lack of clean water during a drought interferes with good hygiene and safe rehydration of those who have lost large amounts of water because of diarrhea or fever," Epstein said.

Floods fuel water-borne illnesse in different ways, writes Epstein. They wash sewage, fertilizer and other sources of pathogens such as cryptosporidium into supplies of drinking water. The concoction can mix with warm water to trigger harmful algal blooms.

Global warming isn't fully to blame for the increase in the spread of infectious diseases, Epstein said. And there are solutions.

Preventive strategies include surveillance systems, satellite monitoring and climate models to predict when conditions are conducive to outbreaks, and a limit on human activities that contribute to global warming exacerbate its effects.

"I worry that effective corrective measures will not be instituted soon enough. Climate does not necessarily change gradually. The multiple factors that are now destabilizing the global climate system could cause it to jump abruptly out of its current state," said Epstein. "At any time, the world could suddenly become much hotter or even much colder. Such a sudden, catastrophic change is the ultimate health risk-one that must be avoided at all costs."