Climate-change impacts on human health can be direct and indirect. Possible direct impacts include changes in the presence of diseases and vectors (vectors are carriers, such as insects, that transmit disease from one host to another) and in the incidence of heat stroke. Indirect consequences could include deterioration of air and water quality.

Health risks associated with climate change for the Northeast, or any region of our nation, are difficult to assess with certainty. Present and potential risks are complicated by factors such as poverty, food quality and availability, sanitation, water quality and availability, the public health infrastructure and access to it, local environmental concerns (indoor and outdoor pollutants), genetics, and lifestyle choices. As a result, climate-change impacts on human health will likely vary among different populations and locales.

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 to be affected by many emerging climate-related health problems is real, 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 impacts have a relatively small impact on health in this region. The health and comfort of those living in the Northeast could, however, be affected by climate changes. Causes for regional concern include: increased incidence of heat waves, increased air pollution, new distributions of infectious diseases and disease carriers, saltwater encroachment into aquifers, alterations in marine ecology, personal endangerment as a result of increased or intensified floods and storms, and potential impacts of droughts on water quality.

Regional characteristics could make some inhabitants and visitors to the Northeast vulnerable to climate-related health changes. Northern regions are projected to experience the largest changes in climate. They are also the location of the greatest loss in stratospheric ozone and the resulting increases in exposure to skin damaging ultraviolet-B radiation. Moreover, because the Northeast is downwind from much of the rest of the country, it receives airborne contaminants from those areas. It also generates its own pollution, especially in the large urban areas. Levels of these contaminants (e.g., ground-level ozone) could be made worse by projected changes in climate.

Infectious and vector-borne diseases (e.g., mosquitoes and the encephalitis viruses they can carry) are extremely sensitive to climate conditions -- especially temperature and humidity. Their geographic distribution changes most in response to changes in minimum (winter and night time) temperatures, which are projected to increase in parts of the Northeast by 4˚ to as much as 10˚F by 2100.

Warm, wet winters combined with warm, wet summers punctuated by heavy rains, climate scenarios that could characterize the Northeast in the next century, can stimulate mosquito breeding and biting. More northerly outbreaks of mosquitoes have occurred in particularly warm years when there have been several days of above 85˚F temperatures. One strain of encephalitis, St. Louis encephalitis, has occurred in the Northeast after heavy rainfall in January and February followed by drought in July. Combinations of such weather events could increase the incidence of eastern equine encephalomyelitis, which can infect humans and horses. Rhode Island and Massachusetts already have experienced outbreaks of this disease.

Climate change also could affect the spread of tick-borne Lyme disease, because tick populations flourish during warm, wet winters. According to the Centers for Disease Control, the Northeast accounts for 90% of the 100,000+ cases of Lyme disease reported nationwide since 1982. However, during the summer, climate change could provide a health benefit to humans vulnerable to tick-borne diseases. This could occur, for example, because ticks, which also can carry ehrlichiosis (a treatable bacterial disease) and a virus that can cause encephalitis, prefer cooler temperatures. If summer temperatures increase as projected for the Northeast, tick populations, and the diseases they carry, could decline.

Despite this potential benefit, a changing climate could aggravate another growing health problem in the Northeast: 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 plantlike dinoflagellates that often are the cause of red-tides. Persistent brown tides (caused by another form of water-borne plants) can reduce oxygen levels in the water, adversely affecting sea grasses and shellfish beds. Another water-borne disease that could affect the Northeast is cholera. Cholera can exist both in the dormant and infectious forms depending on pH (acidity), temperature, salinity, and nutrient levels in the water. Food-borne diseases, such as salmonella, cyclospora, and hepatitis A, also could be enhanced by the warmer, often moister conditions projected for the Northeast.

Other potential environmental impacts on human health include the danger presented by extreme events. The frequencies and/or intensities of floods, hurricanes, droughts, and very hot temperatures, could increase as the climate changes. Each of these extreme events can pose direct and indirect health-related risks to vulnerable populations of the Northeast. Drowning is an example of a direct risk posed by flooding. Flooding can also create an indirect risk by providing new breeding sites for mosquitoes that can carry disease.

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 certain classes of sewage systems, creating a hazard to those consuming contaminated water or contaminated shellfish. Extreme rain events can also 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.

Droughts can also affect human health. Droughts can concentrate microorganisms and populations of pests and, when interrupted by sudden rains, spur explosions of rodent populations that can, among other things, transmit hantavirus pulmonary syndrome. Although incidence of hantavirus is often associated with the Southwest, this disease also has surfaced in the Northeast, particularly in New York and the Mid-Atlantic states. Beyond their role in triggering the growth of harmful organisms, droughts can seriously compromise a region's water supply with impacts that can extend beyond the period of drought. For example, the drought of 1964 had a serious effect on the health of the freshwater estuary of the Delaware River that supplies the Potomac-Raritan-Magothy aquifer. The loss of freshwater run-off during the drought resulted in a pulse of salt water entering the aquifer, causing a permanent change to the aquifer and the need to move some wells in order to reach the unaffected freshwater portion of the aquifer.

The projected trends in the Palmer Drought Severity Index (PDSI) are dependent on the projections of temperature and precipitation. Large increases in drought tendencies occur in the Northeast in the Canadian model associated with substantial warming and small changes in precipitation. In contrast, the Hadley model yields larger increases in precipitation and a more modest warming, conditions under which the drought tendency tends to decline.

While heat and cold are not presently significant causes of death in the Northeast region, cities of the Northeast could experience greater heat-related mortality due to warming. Three important factors play a role in reaching heat-related mortality thresholds: the effect of temperature highs (and when there is no relief at night); consecutive numbers of hot days; and humidity levels. The threshold effect occurs when a stress, for example temperature or number of hot days and nights, goes beyond the level that causes death. Summer heat-related mortality could increase. Although milder winters could reduce some types of winter-related deaths (e.g., heart attack from shoveling snow) in the Northeast, more research is needed to establish the relationship between other types of winter deaths (e.g., flu) and cold temperatures. Still, the total projected increase in heat-related deaths is quite small compared with the region's leading causes of death that are non-climate related. Increasing nighttime and winter temperatures can also be detrimental to human health without causing death. For example, during heat waves, there is less nighttime relief from heat stress. Higher winter temperatures can also favor the viability of pests and pathogens that normally would die-off during the winter months.

The indirect and synergistic (compounding) effects resulting from climate change could also impact the health of those living in and visiting the Northeast. While some populations in the Northeast can likely adapt to the projected (changing) conditions easily, groups such as the urban poor, those on a fixed income, including the elderly, and some of those that participate in outdoor recreation (e.g., hikers in areas downwind of high concentrations of pollutants), might not fare as well. A recent (1991-1992) study of day-hikers on Mt. Washington in New Hampshire, demonstrated the short-term detrimental impacts of ozone concentrations that can vary with elevation. Because of the specific mixing properties of the atmosphere, hiking above approximately 3000 ft. can expose hikers to higher than ground level ozone levels as well as to other airborne pollutants. Even though the average ozone exposure level was +/- 40 ppb (well below the EPA standard of 120ppb), hikers experienced measurable decreases in lung function.

Additional climate-related stresses on the public health infrastructure and the increased incidence of disease could have a wide range of economic impacts on the Northeast. However, it is difficult to quantify future costs.

If the risks of health impacts from climate change increase, intensified public health measures could be needed to combat diseases new to the Northeast or that become more prevalent. Access to public health care, a problem today, could become an even greater problem in the future if demand increases. Because so many people are likely to be affected, health-related coping options could be costly, requiring society to decide the extent of public resources it would be willing to commit to limit or reduce the increasing risk.

Significant direct and indirect costs also could be incurred by relying upon technologies to cope with the changing climate. One example is using air conditioning to address heat-related health problems. The costs of buying an air conditioner and paying the electricity bills could be particularly significant for vulnerable individuals. Costs also could be serious to communities or industry that have to provide additional infrastructure to meet higher electricity demands. Increased electricity demands can result in the indirect impact of increasing the level of greenhouse gases in the atmosphere (unless the energy is generated by alternative sources such as wind or solar).

Many of the costs related to potential health impacts of climate changes could be incorporated into the planning for replacement infrastructure during normal operational lifetimes and be spread out over long periods to avoid larger costs of remedial actions. This incorporation into the long-term planning process, however, requires that the possibility of climate changes be recognized and actively incorporated thus changing the business-as-usual approach that many government and industrial planners practice.

Strategies to address potential impacts of climate change on the health of those residing in and traveling throughout the Northeast are varied in focus and in cost. Some options, listed below, relate generally to health impacts that are felt today as well as in the future, whether they are vector-borne, heat-related, due to low air quality, or the result of extreme events.

• Develop surveillance and response programs to identify and detect emerging diseases and sites of potential vectors, and train physicians and public health workers to recognize and treat emerging diseases.
• Develop an early warning system and preventative programs for populations-at-risk from extreme events, vector-borne diseases, and other potentially health threatening events. Such a warning system could include informing the public about how to maintain their health by, for example, using insect repellents, drinking fluids, and taking cooling breaks during hot weather.
• Support research to investigate methods to curb the proliferation of problematic species, including techniques designed to control vector populations.
• Encourage fortification of sewer systems to better withstand flooding events.
• Encourage the development of programs to assist in better insulating buildings and equipping them with window screens, ceiling fans, and/or air conditioning to prevent the spread of disease and over-exposure to heat.