The 1995 Chicago heat wave led to approximately 600 heat-related deaths over a period of five days. It is now considered to be one of the worst weather-related disasters in Chicago history.
The scale was shocking, although the event itself may not have been that unusual. Eric Klinenberg, author of the 2002 book Heat Wave: A Social Autopsy of Disaster in Chicago, has noted that in the United States, the loss of human life in hot spells in summer exceeds that caused by all other weather events combined, including lightning, rain, floods, hurricanes, and tornadoes....
The temperatures soared to record highs in July with the hottest weather occurring from July 12 to July 16. The high of 106° F (41° C) on July 13 set the record for the warmest July temperature since records began at Midway Airport in 1928. Nighttime low temperatures were unusually high (upper 70s and lower 80s °F - about 25 °C) as well. Record humidity levels also accompanied the hot weather.
Most of the heat wave victims were the elderly poor living in the heart of the city, who either had no working air conditioning or could not afford to turn it on. Many older citizens were also hesitant to open windows and doors at night for fear of crime. Elderly women, who may have been more socially engaged, were less vulnerable than elderly men. By contrast, during the heat waves of the 1930s, many residents slept outside in the parks or along the shore of Lake Michigan.
Because of the nature of the disaster, and the slow response of authorities to recognize it, no official "death toll" has been determined. However, figures show that 739 additional people died in that particular week above the usual weekly average. Further epidemiologic analysis presented by Eric Klinenberg (author of Heat Wave: A Social Autopsy of Disaster in Chicago) showed that blacks were more likely to die than whites, and that Hispanics had an unusually low death rate due to heat. At the time, many blacks lived in areas of sub-standard housing and less cohesive neighborhoods, while Hispanics at the time lived in places with higher population density, and more social cohesion....
A contributing factor in the heat wave is an effect called an urban heat island. Urban heat islands are caused by the concentration of buildings and pavement in urban areas, which tend to absorb more heat in the day and radiate less heat at night into their immediate surroundings than comparable rural sites. Therefore, built-up areas get hotter and stay hotter. Other aggravating factors were inadequate warnings, power failures, inadequate ambulance service and hospital facilities, and lack of preparedness. City officials did not release a heat emergency warning until the last day of the heat wave. Thus, such emergency measures as Chicago's five cooling centers were not fully utilized. The medical system of Chicago was severely taxed as thousands were taken to local hospitals with heat-related problems. In some cases, fire trucks were used as substitute ambulances.
Another powerful factor in the heat wave was that a temperature inversion grew over the city, and air stagnated in this situation. Pollutants and humidity were confined to ground level, and the air was becalmed and devoid of wind. Without wind to stir the air, temperatures grew even hotter than could be expected with just an urban heat island, and without wind there was truly no relief. Without any way to relieve the heat, even the inside of homes became ovens, with indoor temperature exceeding 90 °F (33 °C) at night. This was especially noticeable in areas which experienced frequent power outages. At Northwestern University just north of Chicago, summer school students lived in dormitories without air conditioning. In order to ease the effects of the heat, some of the students slept at night with water-soaked towels as blankets.