When you think about extreme heat, a sweltering, sunny day may come to mind first. But climate scientists are also sounding the alarm on warm summer nights, saying they are quietly becoming a worrisome consequence of climate change — and a serious public health concern.
When nighttime temperatures don’t drop low enough relative to peak daytime heat, it is harder for people to cool off, according to Climate Central, a nonprofit organization that analyzes and reports on climate science.
Extreme heat is the leading weather-related killer in the United States, with heat waves responsible for more deaths than other extreme weather events like tornadoes, flooding or hurricanes, according to the National Weather Service.
Prolonged exposure to high heat in the evenings has been linked to poorer sleep quality, which can impair immune function, exacerbate mental health issues and increase the risk of chronic conditions such as heart disease, according to the Centers for Disease Control and Prevention.
While extreme heat and triple-digit temperatures frequently are the focus of attention and grab headlines, the lack of adequate overnight cooling is also a serious concern that amplifies the impacts of heat. Overnight cooling is essential for not just the human body, but infrastructure and ecosystems to recover after a hot day.
Warmer overnight temperatures are also fueled by urban development. Cities with heat-retaining concrete and asphalt are particularly vulnerable to higher temperatures when vegetation is lost to more paved surfaces and buildings, according to the Environmental Protection Agency.