For many Americans, managing high summer temperatures has become a fact of life. Unfortunately, the human toll of these longer and more intense heat waves is also increasing.

Heat waves — defined by the National Oceanic and Atmospheric Administration as periods of two or more days where the weather is “abnormally and uncomfortably hot” and “outside the historical averages for a given area” — have become more frequent and longer in duration since the middle of the 20th century. In April 2023, 69.7 million Americans lived in counties experiencing higher temperatures than the 20th-century normal.

In 2023, Americans are increasingly grappling with prolonged heat waves — sometimes dubbed “heat domes” or “heat islands” by the Environmental Protection Agency — even in areas accustomed to particularly high heat. Phoenix, Arizona, for example, registered an average daily high temperature of 114.7 degrees Fahrenheit in July.

The impact of intensifying heat on health and population

In 2004, 297 Americans died from excessive natural heat, the lowest figure recorded over the past two decades. In 2018, 1,008 Americans died as a direct result of heat exposure. But in 2021, heat-related deaths increased to 1,600, a 59% uptick from only four years earlier, and a 439% increase from 2004.

Provisional data from the Centers for Disease Control and Prevention (CDC), which actively tracks daily and weekly heat-related illnesses, shows that 1,714 US deaths in 2022 were due to “heat-related” causes.

The CDC notes that older adults, the very young, and people with mental illness and chronic diseases are at the greatest risk for heat-related illnesses and deaths resulting from heat stroke, cardiovascular disease, respiratory disease, or cerebrovascular disease. But even young and healthy people can be affected: more than one in five heat-related deaths occur in Americans aged 15 to 44.

According to CDC data, men are also more vulnerable to heat-related deaths. The number of men who died from heat-related exposure increased from 641 deaths in 1999 to 1,232 deaths in 2022; however, there was no statistically significant increase among women during the same period.

Heat is historically the top cause of US weather-related fatalities

Heat is the leading cause of weather-related fatalities in the United States. The US Natural Hazard Statistics report, published by the National Weather Service and based on CDC data, demonstrates that heat has caused more US deaths yearly than hurricanes and tornadoes combined on average over the past thirty years.

Does FEMA help extreme heat victims?

The Federal Emergency Management Agency (FEMA) does not handle extreme heat situations. As of August 2023, heat isn't listed in the Stafford Act, the federal law that gives FEMA the power to respond to emergencies, meaning that the agency doesn't consider extreme heat a major disaster. Under current laws, FEMA can only provide limited assistance to help people affected by extreme heat, including the purchase of air conditioners or fans to aid in disaster recovery in some cases.

Heat waves are growing in intensity

Recent historical trends demonstrate that increases in the frequency, length, and intensity of heat waves show little sign of abating. At the national level, nine of the 10 warmest years on record for the 48 contiguous states have occurred since 1998. Meanwhile, the number of extreme heat days in some states is five times higher than 40 years ago.

Americans in cities are also at risk from the health impacts of intensifying heat waves. Heat wave seasons — defined as the number of days between the first and last heat wave of a year — are growing longer for US cities, from about 24 days in the 1960s to 73 days in the 2020s. Environmental Protection Agency data notes that the average duration of heat waves per year in metropolitan areas has increased from two days per year to six.

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Read data analyses written by the USAFacts team.

Page sources and methodology

All of the data on the page was sourced directly from government agencies. The analysis and final review was performed by USAFacts.

  • Centers for Disease Control and Prevention

    QuickStats: Deaths Involving Exposure to Excessive Heat

  • Centers for Disease Control and Prevention

    QuickStats: Percentage Distribution of Heat-Related Deaths