In July 1995 the city of Chicago experienced a heat wave that gripped the city for over a week. On July 13th, the heat peaked at 106 degrees. During the week of intense heat, Chicago had turned into an "urban heat island." Most of the city's brick and mortar buildings, along with all the concrete and asphalt streets, absorbed tremendous amounts of heat during the day and released hardly any of this heat overnight. Apartments in the city became ovens.

Then-Mayor Richard M. Daley offered common sense, and stated the obvious. "It's hot. It's hot out there. We all walk out there. It's very, very, very hot," he said. But the heat continued, becoming not just a nuisance but a full-fledged killer. The Cook County Morgue started overflowing with bodies and refrigerator trucks had to be brought in to store the dead. Workers averaged 13 autopsies an hour, but the bodies kept coming. In the end, the heat wave was blamed for 739 deaths.

How did so many people die in a heat wave? When people started to review the official reports and files about those who died, they found a consistent theme: social isolation. The people who died were often elderly and living alone.

In contrast, four years later in 1999, Chicago experienced another heat wave, this one slightly less severe than the 1995 heat wave. By this time, people had stopped denying that heat presented a problem for people living alone. The city responded aggressively to ensure the safety of its residents with strongly-worded warnings, and city workers went door-to-door to check on seniors and other vulnerable people and kept cooling centers open. Due to these outreach efforts only 125 people died in the '99 heat wave.

Editor's Note: Most of the research about those who died was conducted by an urban sociologist named Eric Klinenberg, as reported in his book Heat Wave: A Social Autopsy of Disaster in Chicago, especially his chapter "Dying Alone: The Social Production of Isolation."