Most people know that heat waves can be dangerous. What they may not realize is that the heat indoors can be much worse than outdoors.
When the power goes out and air conditioning stops, a house starts to function like a greenhouse. Heat enters through windows and walls and has nowhere to go. Air stagnates.
Within hours, indoor temperatures can climb well above what the thermometer shows outside, especially on upper floors and in rooms with south-facing windows. Over longer periods, especially if temperatures don't cool off overnight, conditions can become lethal.
Most heat-related deaths occur indoors. When a heat dome sent temperatures soaring in the Pacific Northwest in 2021, 98% of the more than 600 deaths in British Columbia happened inside homes. Washington and Oregon also saw high numbers of deaths in homes that lacked air conditioning.
In Europe, where only 1 in 10 households have air conditioning, heat waves killed an estimated 60,000 people in 2022 and 47,000 in 2023, largely inside buildings never designed for these temperatures.
