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Climate-change effects on human health can be direct, such as might result from changes in the range of diseases and vectors (vectors are carriers, such as insects, that transmit disease from one host to another) or in the incidence of heat stroke. In addition, climate change can produce indirect affects on human health, such as by worsening air pollution and water quality that in turn would affect human health.
Health risks associated with climate change -- for the Southeast or any region of our nation -- are difficult to project with certainty. Present and potential risks are complicated by factors such as poverty, food quality and availability, sanitation, water quality and availability, public health infrastructure and access to it, local environmental concerns (indoor and outdoor pollutants), genetics, and lifestyle choices. As a result, climate-change affects on human health will likely vary among different populations and locales. Maintaining and improving public health infrastructure is critical in responding to the potential impacts on human health from climate changes.
It should be noted that the US public health infrastructure has developed the capacity and experience to manage numerous public health risks to US populations and thereby reduce the vulnerability of those populations. While the potential exists to be affected by many emerging climate-related health problems, at the same time many of these risks can be effectively dealt with by preventative actions.
For example: a heat wave increases the risk of heat-related mortality, but establishing warning systems and air conditioned locations open to the public will reduce the vulnerability of those populations at risk. While this and other risk reducing, adaptive and preventative measures are available, they are not without costs. Some of those costs relate to the actual activity undertaken, some relate to maintaining the public health infrastructure, some relate to the impacts of the coping mechanisms chosen, and some relate to effectively reaching subgroups with less access to public health options.
At present, climate related health affects are a very small determinant of health in this region. The health and comfort of those living in the Southeast could, however, be adversely affected by climate changes. Causes for regional concern include an increased frequency and intensity of heat waves, increased air pollution if additional controls are not implemented, wider occurrence of infectious diseases and disease carriers, increased saltwater encroachment into aquifers, and alterations in marine ecology, storms, and droughts.
Because changes in the Southeast's climate could have intertwined environmental and social impacts on human health, they are discussed jointly next. Economic impacts and strategies to minimize potential impacts are addressed in the following subsections.
Infectious and vector-borne diseases (e.g., mosquitoes and the encephalitis viruses, malaria, and dengue they can carry) are extremely sensitive to climate conditions -- especially temperature and humidity. Their potential geographic distribution changes in response to changes in minimum temperatures, although their actual distribution depends on control measures and even more on the ability of the public health infrastructure to avoid outbreaks. In fact, largely due to control measures, the latest model results suggest that with the exception of a few areas (like Brownsville, TX and southern Florida), there is little evidence of increased vector-borne disease actually projected for the Southeast.
Although its occurrence in the US is very rare due to control measures, warming trends and increases in precipitation can increase or shift the range of malaria to higher latitudes or altitudes. Similarly, decreases in precipitation could be expected to shrink the potential areas for malaria transmission. For the most part, malaria has been eradicated from the US for many years and socioeconomic factors such as living conditions and the ability of the public health infrastructure to cope are the largest factors in controlling actual malaria cases. However, malaria-carrying mosquitoes have the potential to do better under projected climate change.
There is also a renewed concern because locally transmitted malaria has been reported throughout the 1990s in Georgia, Florida, and Texas. Warmer, wetter winters combined with warm and wet summers, or drought punctuated by heavy rains, can stimulate mosquito breeding and biting. In addition, similar conditions would shorten the parasite extreme incubation period (EIP), the number of days between the mosquito's ingestion of infected blood and the point when it becomes able to transmit the infection. Malaria's EIP period shortens at temperatures between 68°F and 82°F, which means the carriers are infectious sooner and for a longer time period.
A changing climate could aggravate another growing health problem in the Southeast: the incidence of red tides, fishkills, and bacterial contamination in shellfish. Hotter summers favor more toxic forms of water-borne plants, such as blue-green algae and the dinoflagellates that often are the cause of red tides. Persistent brown tides (caused by excessive growth of other noxious aquatic plants) can reduce oxygen levels in the water, affecting sea grasses and shellfish beds, and a whole host of marine organisms. In 1987, this region experienced an outbreak along the East Coast that caused substantial fish kills and associated human illness attributable to shellfish poisonings. One place that has experienced significant reductions in oxygen content is along the Louisiana coast.
Flooding, often a result of storm waves, hurricanes, and torrential rain, is dangerous for several reasons beyond the obvious and direct danger to humans of drowning and damage to property. It has also been associated with outbreaks of Cryptosporidium, Giardia, and E. coli -- all illness-causing organisms transmitted from human or animal wastes. Extreme rain events can overwhelm the capacity of sewage systems, causing a temporary closing of shellfish beds and a hazard to those who consume contaminated shellfish. Fresh water quality can also be directly affected by extreme weather events such as flooding.
Extreme rain events increase run-off from farms causing a release of bacteria and such organisms as Cryptosporidium into the environment and into water supplies. Cryptosporidiosis is a concern but not a serious problem for otherwise healthy people. It is, however, a potentially deadly disease for those who are immuno-compromised by other factors. It can also be a problem because once the Cryptosporidium organism is in a water supply it is difficult to remove. For example, the public water supplies in eastern North Carolina were fouled with sewage, rotting farm animal carcasses, chemicals, and fuel after the 1999 floods that overwhelmed that area leaving the populous without safe and sanitary drinking water. The frequency of extreme rain events could increase with climate changes. Determining the changes in the frequency of other extreme events is an area that requires more study.
Droughts can also contribute to serious health concerns for individuals and communities. Droughts especially concentrate pollutants and microorganisms. Moreover, droughts interrupted by sudden, intense rains spur explosions of pest populations, e.g., rodents that can transmit hantavirus pulmonary syndrome. Although incidence of hantavirus is often associated with the Southwest, this disease also has surfaced sporadically in North Carolina, Florida, Louisiana, and Texas.
Three important factors play a role in reaching heat-related mortality thresholds: the maximum temperatures (including nighttime highs); the consecutive numbers of hot days; and humidity levels. The threshold effect occurs when a stress, for example temperature or duration, goes beyond the level that causes death. High nighttime temperatures during heat waves provide less relief from the stressful daytime heat. Heat-related deaths in cities of the Southeast (200 during the heat wave of 1998) would be aggravated by increasing numbers of consecutive hot days and because the projected changes in the heat index (increases in temperature as well as humidity) for this region are the most dramatic in the nation.
The indirect and synergistic (compounding) effects (e.g., increases in the number of days with high concentrations of ozone [an air pollutant]) resulting from climate changes could also impact the health of those living in and visiting the Southeast. While some populations in the Southeast can adapt to these conditions easily, groups such as the urban poor, those on a fixed income, including the elderly, and some that participate in outdoor recreation, might not fare as well.
Increased climate-related stresses to human health and the public health infrastructure could have a wide range of economic impacts on the Southeast. However, it is difficult to quantify future costs.
If the health effects from climate change increase, better public health infrastructure is likely to be important in limiting new diseases in the Southeast and that deal with diseases that become resistant to existing drugs. For example, the most virulent form of malaria, Plasmodium falciparum, has become drug-resistant, and antimalarial vaccines have shown only limited effectiveness. Access to public health service -- a problem today -- could become an even greater problem tomorrow as demand grows. These and other coping options could be costly, requiring society to increase the public resources to address these issues. While public health practices will likely keep vector-borne epidemics at bay, the environment is also likely to become more suited to having isolated cases of diseases breakout. Even isolated cases of disease can create public fears that can drive away tourists, who are major contributors to the regional economy.
Past episodes of toxic red tides and brown tides -- events expected to increase with climate change -- already have poisoned fish populations and shellfish beds, which in turn have created neurological and other health problems and caused expenses for treatment among those who consumed tainted fish products. The future cost of addressing such health problems, as well as the economic damage done to the fishing industry, is extremely difficult to quantify.
Significant direct and indirect costs also could be incurred in dealing with the direct effects of warming. For example, if increased reliance on air conditioning is needed to alleviate heat-related health problems, then there are numerous costs associated with that choice. These costs could be significant to individuals -- to weather-tighten their homes, to buy the air conditioner, and to pay the electricity costs. There would also be costs of providing the additional infrastructure to meet higher electricity demands. Increased electricity demands also could result in the indirect effect of increasing the level of greenhouse gases in the atmosphere and thereby increasing the amount of warming resulting in more air conditioning needed.
The strategies available to address effects on human health in the Southeast would vary in focus and cost. These options, listed below, relate generally to health effects whether they are heat-related, vector-borne, or the result of extreme events. This list should be viewed as only a starting point and includes some activities already being undertaken in some locations and that could be extended or continued.
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