Extreme heat has become the deadliest weather-related hazard in the United States, killing an estimated 1,300-2,000 Americans annually through direct heat illness — more than hurricanes, tornadoes, and floods combined — and contributing to the deaths of an additional 5,000-7,000 Americans through cardiovascular and respiratory conditions exacerbated by high temperatures.
The trend is accelerating. The number of days with heat index values exceeding 100°F in major US cities has increased 45% since 1980, and 2023 was the hottest year in recorded US history. Phoenix, Arizona recorded 31 consecutive days above 110°F last summer — a record for any major US city. Miami, Atlanta, Dallas, and Houston all recorded their hottest summers ever.
The vulnerable populations bear the greatest burden. Outdoor workers — largely Latino and Black Americans in agriculture, construction, and landscaping — face daily heat exposure that is unambiguously dangerous and largely unregulated. The US lacks a federal heat standard for outdoor workers, despite OSHA having the authority to create one since 1970. California, Colorado, Washington, and Oregon have passed state heat standards; the other 46 states have not.
Urban heat islands — cities that are 8-15°F hotter than surrounding rural areas due to heat-absorbing pavement and reduced tree cover — concentrate heat mortality in low-income urban neighborhoods that lack access to air conditioning. A 2023 federal study found that the 50 US counties with the highest heat mortality rates also had the lowest median incomes.
