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Another predicted consequence of global warming is heavier downpours, leading to more floods. The immediate hazard is drowning, but the larger issue is water quality. To take just one example, more than 700 U.S. cities--most of them older communities in the Northeast, Northwest and Great Lakes area--have sewer systems that regularly overflow into water supplies during heavy rainstorms, mixing dirty and clean water and sometimes requiring mandatory boiling to make contaminated tap water safe. A heavy rainfall preceded the majority of waterborne-disease outbreaks in the U.S. over the past 60 years, says Dr. Jonathan Patz of the University of Wisconsin at Madison.
Ocean-water patterns also play a role in human health. Mercedes Pascual and her colleagues at the University of Michigan have been poring over more than a century's worth of data on cholera outbreaks in Bangladesh and tying them to detailed temperature reports of the surface waters of the Pacific Ocean. True, Bangladesh isn't anywhere near the Pacific, but the researchers are using the temperature data as an indication of a larger weather pattern called the El Niño/ Southern Oscillation, or ENSO. What they have found is that the severity of an epidemic is linked to water temperature--but only in years of higher-than-normal temperatures on the ocean's surface. More alarming: as the ENSO pattern has become more pronounced since the 1970s, the association with cholera has become even stronger.
INSECTS The news here is not all bad. Ticks, for example, may not be able to survive hotter temperatures in the southwestern U.S. And global warming is unlikely to have much of an effect on malaria, as long as you focus on lowland areas (because those regions already have so many mosquitoes). That picture may change, however, as you move upward in elevation. Malaria has seen a dramatic upswing since the 1970s in highland cities like Nairobi (around 5,500 ft. above sea level). How much of that can be tied to temperature increases--as opposed to population movement, lapses in mosquito control or the spread of drug-resistant parasites--is a matter of debate. But because each year there are at least 300 million cases accounting for more than 1 million deaths, even a small uptick in the spread or severity of malaria could be devastating.
The tricky thing about all those predictions is that you can't point to any outbreak or any individual's death and say, "This occurred because of climate change." But we know that good public health relies on a long list of factors--the availability of doctors and nurses, effective medicines, clean water, proper sanitation--and that even today, millions of people die every year of what should be preventable diseases. With global warming, you can expect the death toll to be even higher.