Human Health

Climate change has the potential to impact human health directly through, for example, 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 could produce indirect impacts on human health through increases in air pollution and decreases in the quality of the air and water. Possible climate-related threats to the health of those living in the Great Lakes region include increases in severe smog; air-borne-allergens, acid rain, and toxins; altered distributions of infectious diseases and carriers; harmful alterations in aquatic ecology; and increased incidence of extreme weather events, such as floods and droughts.

The Great Lakes region is also particularly vulnerable to the pollutants that are transported here from other regions of our nation and Canada. Increased levels of pollutants can have synergistic (enhanced effectiveness) impacts when combined with other current and potential health stresses. Health risks to those living in this region are difficult to assess with certainty, however, and can be expected to be complicated by factors such as wealth (e.g., the level of poverty), the quality and availability of food and water, sanitation, the adequacy of the public health infrastructure, and local environmental factors. Thus, the impacts on human health resulting from climate change would be likely to be different for different populations in the region. Maintaining and improving public health infrastructure is critical in responding to the impacts on human health resulting from climate change.

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.

Photochemical smog, high levels of ground-level ozone, and inhalable and respirable particulates already reduce air quality in the Great Lakes region. New research is pointing to the possibility that even low levels of ground-level ozone may adversely affect human health (see hiker health study in the NE region), as well as affecting crop yields and the health of forests. Moreover, ozone levels are aggravated by the Great Lakes because water, unlike land, does not absorb ground level ozone. Ozone and its precursors, which react in the presence of sunlight to form it, can therefore be trapped in lake breeze circulations. Ground-level ozone and other air pollutants can compromise the respiratory systems of otherwise healthy people, but generally pose even greater risk to the elderly, small children, and asthmatics.

Currently, one county in Michigan and five in Wisconsin are frequently unable to meet the National Ambient Air Quality Standards. The Great Lakes region, in general, receives polluted air from other regions and transports its own smog and ozone precursors by winds directed northward and eastward. However, climate change could affect the level and the transport of pollutants in several ways.

In general, three meteorological factors affect smog levels: temperature, changing weather patterns, and changing local conditions. First, higher temperatures worsen air pollution by increasing power demands and related emissions in summer. Increasing temperatures also increase the rate of chemical reactions that form smog and ozone, thereby increasing the "effectiveness" of pollution formation by precursors (a substance from which another substance is formed) found in emissions. Second, the movement of large air masses can be a major contributor or remover of smog, and changing weather patterns could affect the characteristics and frequency of crucial air-transport patterns to either the detriment (stagnation) or benefit (increased movement) of the area. Finally, local effects in the Great Lakes region include changing the ‘lake effect' on local weather. The changes in day-to-day weather conditions can drastically affect ozone levels, causing levels to exceed acceptable ranges; year-to-year variations in climate can also have effects by changing emissions and the level of outside activity.

Climate variability also could impact human health in this region through increased air transport of air-borne allergens, exacerbating asthma and hay fever; acidics (acid rain); and toxins. Anywhere from 14 to 90 % of some pollutants arrive in the Great Lakes region on air currents, with some having been transported a long distance. For example, toxaphene, a pesticide that was used extensively in cotton fields of the southern United States and has been banned for 20 years, is still being emitted from the soil and transported long distances. Changes in weather patterns resulting from climate variability have the potential to affect the incidence of such events.

Infectious and vector-borne diseases are sensitive to climate conditions and could have an impact on human health in the region. Changes in minimum temperatures (e.g., winter and nighttime) affect the geographical distribution of the occurrence of many of the vectors. This occurs because many disease vectors prefer the warm, moist conditions that are expected to extend over a wider geographic range with climate change.

For example, warm and wet winters combined with warm and wet summers or drought punctuated by heavy rains -- conditions projected to become more frequent with climate change -- are observed to stimulate mosquito breeding and biting. Mosquitoes, and the encephalitis viruses that some carry, are responsive to such factors as temperature and humidity. Northerly outbreaks of St. Louis encephalitis have occurred in particularly warm years with periods of above 85° F temperatures, excessive rainfall in winter and drought in summer. Similar weather events could increase the incidence of eastern equine encephalomyelitis, which can infect humans and horses and already has been a problem in Michigan.

Further, temperature and humidity are among the main climate factors in the transmission of malaria. Malaria has been observed to be present primarily in humid regions with average temperatures above 61_ F. Warming trends and increases in precipitation could increase or shift the range of potential malaria outbreaks to higher latitudes or altitudes. One climate model suggests the possibility of malaria outbreaks as far north as Toronto, although it must be noted that temperature and humidity are not the only factors that influence outbreaks of this disease. Socioeconomic factors such as living conditions and the ability of the public health infrastructure to cope with such situations are the most decisive factors in controlling actual malaria cases. The US public health system has been very effective in preventing the spread of malaria and numerous other infectious and vector-borne diseases and will very likely continue to be an effective protector of community-wide human health, even if an increased number of isolated cases occur.

Climate change also could affect the spread of tick-borne Lyme disease. The incidence of Lyme disease in the region in 1996 exceeded 16,000 cases, an increase of 37 % over the previous year, with Wisconsin and Minnesota having had high numbers of cases in the 1990s. However, warmer conditions could also provide some health benefits. Ticks, which also can carry ehrlichiosis (a treatable bacterial disease) and a virus that can cause encephalitis, prefer cooler conditions and summer incidence could actually decline if temperatures warm significantly.

Warmer conditions also are likely to affect water-borne organisms. Hotter summers tend to increase photosynthesis and the metabolism of algae (aquatic plants such as seaweed and pond scum), favoring more toxic forms of water-borne algal blooms, such as cyanobacteria and dinoflagellates. Nuisance and persistent blooms can reduce oxygen levels in the water, compromising aquatic grasses, shellfish beds, and other aquatic organisms. In addition, pollutants in the water render the fish less healthy for human consumption. Hotter summers also promote stratification of deep lakes (more quickly), which can reduce useful algae production. Any contact with water-borne pollutants can pose a health danger to humans; an increase in hot weather can lead to more frequent swimming, even in unsuitable locations, putting swimmers at increased risk of disease.

Extreme events such as floods, storms, and droughts could continue to present direct and indirect health-related risks to populations. An example of a direct risk would be the heightened threat of drowning from flooding (a problem more in the streams and rivers in the region than in the Great Lakes). An indirect risk could include destruction or interference with the operation of a community's water sanitation systems if flooding occurred.

In addition to endangering life and property, flooding can present serious risks to human health. Flooding has been associated with outbreaks of cryptosporidia and giardia, which are resistant to disinfecting measures taken by many municipalities, and of E. coli. During extreme rain events, bacteria can be washed out of the sewage treatment plants (sometimes through combined sewer overflows) and into the environment. Flooding also promotes fungal growth and provides new breeding sites for mosquitoes, which can then increase disease transmission rates. Such threats to human health could rise if flooding increased with climate change, although many of those concerns are likely to be satisfactorily addressed by the public health infrastructure that is already in place in the region.

The frequency of storms and heavy rain events increased in the Great Lakes region during the 20^th century. The incidence of storms increased mostly before 1950 and heavy rain events have increased 20% in the last 15 years, with the century's highest number of heavy rain events occurring between 1991 to 1995. Both storms and extreme rain events could pose significant harm to human health if they were to increase in frequency or severity during the 21^st century. However, caution is needed in using climate models to project changes in the intensity and frequency of floods and other extreme weather events because there are still numerous uncertainties when down-scaling model outputs from global to local scales.

Although overall precipitation is expected to increase in the Great Lakes region, changes in the distribution of precipitation and the intensity with which precipitation falls could result in increased incidence of droughts. Droughts can concentrate microorganisms and, when interrupted by sudden rains, spur explosions of rodent populations, which can carry the virus that causes hantavirus pulmonary syndrome expression in humans. Although this virus is more commonly associated with the Southwest, it has also emerged in Wisconsin and Minnesota. Moreover, in the summer of 1997 an Owen Sound, Ontario resident died from hantavirus, the first known fatality in Ontario from this disease.

Heat-related deaths in cities would be likely to be aggravated by warming, both through changes in the maximum temperature reached and through an increase in the number of consecutive hot days. Increasing nighttime temperatures -- in other words, a rise in minimum temperatures -- also could be directly detrimental to human health. During heat waves, there would be less nighttime relief from heat stress. The maximum temperature effect occurs when a stress, either high temperature or the number of days (and nights) with high temperatures, continues beyond the level where mortality rises rapidly. Summer heat-related mortality in this region has the potential to be significantly increased. For example, projections suggest that a 3_F warming in Milwaukee could almost double the present number of heat-related deaths during the summer months. Although some groups can adapt to these conditions easily, other groups, such as the urban poor may not be able to afford to adapt by, for example, acquiring air conditioning.

Transportation and the risks it places on human health also are a consideration for the Great Lakes region. Each year, many vehicle occupants, motorcyclists, cyclists, and pedestrians are killed or injured in traffic accidents. That number could change with an increase in extreme weather events and changes in the freeze/thaw cycle, increased precipitation events, or changes in snow and ice events. On the other hand, with the long-term projected reduction in overall snowfall (even though there is likely to be an increase in Lake effect snowfall during the transition time), fewer fatalities are likely to eventually result from winter driving hazards.

The economic impacts of potential health-related problems in the Great Lakes region remain uncertain. Additional climate-related stresses on the public health infrastructure could have a wide range of economic impacts on the Great Lakes region. However, it is difficult to quantify future costs.

If the risk of health impacts from climate change increases, intensified public health measures could be needed. Access to public health care, a problem today, could become a greater problem in the future. Because so many people are likely to be affected, health-related coping options could be costly, requiring society to increase public resources to address the issues.

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 the 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.

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 the larger costs of remedial actions. Such an incorporation of the potential consequences of climate change into the long-term planning process, however, requires that the issue be recognized by changing the business-as-usual approach that many government and industrial planners practice.

Strategies that could help cope with potential climate-change impacts on human health in the Great Lakes region are varied in focus and in cost. Many of the options are tailored to address specific health problems, such as those caused by pollution, disease, and extreme events. They could include efforts to:

• Enhance surveillance and response programs that focus on detecting and identifying emerging diseases and the cycles and locations of potential vectors;
• Offer more extensive educational opportunities to physicians, public health workers, and communities to help them recognize and treat emerging diseases;
• Investigate methods of curbing the proliferation of problem species, including techniques designed to control vector populations associated with certain diseases;
• Inform the public about potential threats to their health and how to respond (for example, applying insect repellents, maintaining hydration, and taking breaks from activity during hot weather);
• Identify populations at-risk for heat-related problems, vector-borne diseases, and extreme events, and offer preventative programs targeted to these groups;
• Develop a weather-related early warning system for at-risk populations;
• Better insulate buildings and equip them with window screens and air conditioning to prevent the spread of disease and overexposure to heat; and
• Fortify sewer systems to withstand extreme events, such as storms and floods.