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Climate Change Impacts:
Human Health
Human health concerns related to climate change result from a complex set of interacting human and environmental factors. These concerns are particularly serious for the elderly and other vulnerable populations (the very young, the poor, and those whose health is already compromised). Climate change projections suggest that extreme heat periods and severe storms are likely to become more common in the Great Lakes region. As a result, air and water quality, extreme heat periods, and storm-related risks could increase for residents of Pennsylvania. Among the concerns are:

• Increased Risk of Heat-Related Morbidity or Mortality
  Of the course of the century the number a hot day (exceeding 90^oF) a year in the region is projected to increase reaching 40 or more days a year. Of even greater concern is the projected increase in extreme heat days (exceeding 97^oF). Extreme heat is associated with cramps, fainting, heat exhaustion, and heat stroke; and lengthy or repeated heat waves may not allow people to recover. The ill-health effects of heat waves may also be compounded by other problems, such as high humidity and poor air quality. In order to avoid the worst health impacts, residents will need to improve warning systems and preparations.
  
  
• Decreased Risk of Cold-Related Morbidity or Mortality
  Cold-related health risks are likely to decline over time, as the frequency of extreme cold weather periods during winter decreases.
  
  
• A Potential Increase in Ground-Level Ozone
  Weather conditions conducive to high ozone levels will occur more often over the next decades, and high heat days may lead to decreased air quality and an increased incidence of respiratory disease. Ground-level ozone is produced by a complex series of chemical reactions involving sunlight, oxygen, water vapor, volatile organic compounds, and oxides of nitrogen. The rates of these reactions increase with higher temperatures. Thus, as Pennsylvania grows warmer, the formation of ground-level ozone, holding air pollutants constant, will increase. Research is underway to assess what may happen when temperatures rise but air pollutants are reduced.
  
  
• Increased Risk of Waterborne Infectious Disease
  Extreme rainstorms can swamp municipalities' sewage and stormwater capacities, increasing the risks of water pollution and waterborne infectious diseases. As a result, outbreaks of waterborne infectious diseases such as cryptosporidiosis or giardiasis may become more frequent or widespread if extreme rainstorms occur more often, as projected under climate change.
  
  
• Increased Risk of Vector-borne Infectious Disease
  The occurrence of many infectious diseases is strongly seasonal, suggesting that climate plays a role in influencing transmission. St. Louis encephalitis outbreaks in the Great Lakes region, for example, have been associated with extended periods of temperatures above 85°F (29°C) and little rainfall. Some Vector-borne diseases such as Lyme disease or, more recently, West Nile encephalitis have expanded widely across the region. While this spread is attributed largely to land use changes, future changes in rainfall or temperatures could encourage greater reproduction or survival of the disease-carrying insects, which include ticks and mosquitoes, respectively.