• Climate change will increase the frequency and severity of extreme heat events such as heat waves. In the U.S., heat waves are the most dangerous extreme weather event we face; they cause more than 1,300 deaths per year.
  
  
• The body's reaction to extreme heat begins with rashes and cramps and can progress to heat exhaustion and, eventually, heat stroke.  Heat stroke can cause delirium, convulsions, coma, and even death.

• Hotter temperatures lead to an increased risk for people suffering from chronic cardiovascular, respiratory, and mental health disease and diabetes.

• Heat also contributes to the formation of ground-level ozone, a dangerous and widespread pollutant.  Ozone exposure contributes to asthma attacks and exacerbates existing lung disease.  It also increases the risk of premature death from cardiovascular disease, strokes, and respiratory causes.

• Children and athletes generally spend more time outdoors, making them more susceptible to dehydration, electrolyte imbalance, fever, and renal disease.
  
  
• Dehydration caused by higher temperatures can cause the release of labor-inducing hormones, provoking preterm births among pregnant women.
  
  
• Elderly people and children are vulnerable because their bodies have less ability than adults' to regulate their internal temperature.
  
  

  How you can protect yourself
  and your neighbors:

• Use air conditioning during extreme heat.  If you go outdoors, keep cool by staying in shaded areas and staying hydrated.

• Take extra steps to protect others. Encourage your city to adopt policies to prepare residents and strengthen infrastructure for heat waves:  educate citizens about heat waves, form programs to provide neighborhood check-ins during heat waves, offer cooling centers where residents can avoid the heat. Some cities have taken steps to lessen the impact of heat by building green roofs and green areas.

• Urban areas have longer, hotter summer days due to the "urban heat island" effect. This phenomenon occurs as asphalt and buildings absorb heat during the day and emit that heat during the night, forcing residents to deal with prolonged and unrelieved high temperatures. This is extremely dangerous for individuals who don't have access to, or can't afford, air conditioning, or live surrounded by tall buildings that reduce ventilation.

"Temperature extremes most directly affect health by compromising the body's ability to regulate its internal temperature. Loss of internal temperature control can result in a cascade of illnesses…also worsen chronic conditions such as cardiovascular disease, respiratory disease, cerebrovascular disease, and diabetes-related conditions. Prolonged exposure to high temperatures is associated with increased hospital admissions for cardiovascular, kidney, and respiratory disorders."
-U.S. Global Change Research Program (see below)

This figure shows the relationship between high temperatures and deaths observed during the 1995 Chicago heat wave. The large spike in deaths in mid-July of 1995 (red line) is much higher than the average number of deaths during that time of year (orange line), as well as the death rate before and after the heat wave. This increase in the rate of deaths occurred during and after the heat wave, as shown here by temperatures exceeding the 100 degree F during the day (green line). Humidity and high nighttime temperatures were also key contributing factors to this increase in deaths (Karl, T. R., and R. W. Knight, 1997). The number of excess deaths has been estimated to be about 700 based on statistical methods, but only 465 deaths in Cook County were classified as "heat related"  on death certificates during this same period, demonstrating the tendency of direct attribution to undercount total heat-related deaths(Centers for Disease Control and Prevention, 1995). (Figure source: EPA, 2012)

Centers for Disease Control and Prevention (CDC), 1995: Heat-related mortality--Chicago, July 1995. Morbidity and Mortality Weekly Report, 44, 577-579
EPA, 2012: Climate Change Indicators in the United States, 2nd Edition. 84 pp., U.S. Environmental Protection Agency, Washington, D.C.
Karl, T. R., and R. W. Knight, 1997: The 1995 Chicago heat wave: How likely is a recurrence? Bulletin of the American Meteorological Society, 78, 1107-1119. doi:10.1175/1520-0477(1997)07
USGCRP, 2016: The Impacts of Climate Change on Human Health in the United States: A Scientific Assessment. Crimmins, A., J. Balbus, J.L. Gamble, C.B. Beard, J.E. Bell, D. Dodgen, R.J. Eisen, N. Fann, M.D. Hawkins, S.C. Herring, L. Jantarasami, D.M. Mills, S. Saha, M.C. Sarofim, J. Trtanj, and L. Ziska, Eds. U.S. Global Change Research Program, Washington, DC, 312 pp.  http://dx.doi.org/10.7930/J0R49NQX

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