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Record-Breaking Heat Deaths Mark a Turning Point in American Health
The summer of 2023 shattered records in the most devastating way possible. An Associated Press analysis of federal data shows that about 2,300 people in the United States died in the summer of 2023 with their death certificates mentioning the effects of excessive heat. That’s the highest in 45 years of records. But here’s what keeps health experts awake at night: those official numbers are just the tip of the iceberg. According to their methods, Lee said, about 11,000 heat deaths likely occurred in 2023 in the U.S. based on excess death studies that paint a much grimmer picture. The difference between these numbers reveals how dramatically we’re underestimating this crisis.
When Heat Meets Pollution, Death Rates Soar
Scientists have discovered something terrifying: when extreme heat and air pollution collide, they don’t just add to each other’s harm – they create a deadly multiplication effect. The study found that compared to days without extreme conditions, extreme heat days carried a 6.1% increase in risk of death. On extreme air pollution days, deaths were 5% more likely. But on days with both extreme heat and air pollution, deaths were 21% more likely—a synergistic effect almost double the impact of the individual exposures combined. This finding from USC researchers analyzing 1.5 million deaths across California reveals we’re facing a new type of environmental emergency. The combination creates what scientists call a “synergistic effect,” where the whole becomes deadlier than the sum of its parts.
America’s Air Quality Crisis Deepens Despite Decades of Progress
According to the new report, people in the U.S. experienced the most days with “very unhealthy” and “hazardous” air quality due to particle pollution in 25 years. In total, the report finds that 131 million people (39%) are living in areas with unhealthy levels of air pollution. Even more alarming, the 2025 State of the Air report shows the situation is getting worse. Nearly half of the people living in the U.S. breathe unhealthy levels of air pollution, according to the American Lung Association’s 2025 “State of the Air” report, which was released today. In total, the report finds that 156 million people, 25 million more than last year’s report, are living in areas that received an “F” grade for either ozone or particle pollution. This represents nearly half of America’s population breathing dangerous air.
The Southwest Emerges as Ground Zero for Heat-Health Disasters
The American Southwest is becoming a laboratory for understanding how extreme heat kills, and the results are shocking. Nearly three-quarters of the heat deaths last summer were in five southern states that were supposed to be used to the heat and planned for it. Except this time they couldn’t handle it, and it killed 874 people in Arizona, 450 in Texas, 226 in Nevada, 84 in Florida and 83 in Louisiana. What makes this particularly frightening is that these aren’t northern cities caught off guard by unusual heat waves. The average HRI ED rates in 2024 are higher in 9 out of 10 HHS regions when compared to the average rates in 2023. Notably, HHS region 9 (which includes most of the Southwest and Hawai’i) is at nearly twice its already high 2023 rate, and the rates for HHS regions 2 and 3 (which include the mid-Atlantic region and Caribbean) are more than twice what they were this time last year.
2024 Becomes Earth’s Hottest Year, Breaking Every Climate Record
The European Union’s Copernicus Climate Change Service has officially declared 2024 the hottest year on record, and the first year in history with an average global temperature rising 1.5° Celsius (2.7° Fahrenheit) above the pre-industrial period — significantly increasing dangerous climate risks. In fact, 2023 and 2024 may well be the hottest years in 100,000 years, with all indicators pointing to it getting hotter, bringing ever-worsening global impacts. This milestone isn’t just a number – it represents a fundamental shift in the planet’s climate system. 2024 was the warmest year on record and the last 10 hottest years have all occurred in the last 10 years. Climate models suggest that global surface temperature could rise between 1.5 °C and 5.5 °C compared with the pre-industrial period by 2100, and sea-level rise could be between 0.5 m and 1.3 m. We’re witnessing changes that will reshape human health for generations.
Ground-Level Ozone Creates Invisible Death Traps in Cities
Heat doesn’t just kill directly – it transforms urban air into a toxic soup that attacks the lungs and heart. Ground-level ozone is formed when nitrogen oxides and volatile organic compounds (VOCs), emitted from vehicle exhausts and other combustion sources such as factories, react with sunlight. A recent analysis by the Centre for Science and Environment (CSE), a Delhi-based think tank, found that new hotspots for ground-level ozone emerged across the city over the summer. Between April and July 2024, Delhi recorded ground-level ozone readings in excess of safe limits on 102 days, often for more than 13 hours at a stretch, the analysis said. This chemical reaction accelerates in extreme heat, turning everyday pollution into a respiratory nightmare. After years of progress on cleaning up ozone, some communities are seeing the worst ozone levels in years. More than 125 million people (37% of the nation’s population) lived in an area with unhealthy ozone pollution, which is 24.6 million more than last year’s report. Extreme heat and wildfires contributed to the increase in ozone levels for many parts of the country, most notably in central states from Minnesota to Texas.
Vulnerable Communities Bear the Heaviest Burden
The deadly combination of heat and pollution doesn’t strike everyone equally – it targets the most vulnerable with surgical precision. The rate of heat-related mortality tended to be higher among males, persons aged ≥65 years, non-Hispanic American Indian/Alaska Natives, and persons living in noncore nonmetropolitan and large central metropolitan counties. Observed differences in heat-related mortality across racial/ethnic groups can also be associated with social vulnerability, which often tracks with factors leading to heat exposure (e.g., less green space and more heat-absorbing surfaces), health disparities manifested by lower income, and absence of structural adaptations such as air conditioning. People of color and low-income communities face what researchers call “environmental injustice” – they’re more likely to live in heat islands with worse air quality and less access to cooling. Individual exposure to heat is associated with adverse health and economic outcomes. Here, the authors show that people of color and people living in poverty bear a disproportionate burden of urban heat exposure in almost all major cities in the continental United States.
Emergency Rooms Become Battlegrounds Against Heat Illness
Hospital emergency departments are witnessing an unprecedented surge in heat-related visits that’s overwhelming healthcare systems across the country. Across five southern states, the average rate of emergency department visits for heat illness in the summer of 2023 was over double that of the previous five summers, according to an analysis of data from the CDC. Healthcare workers are reporting cases they’ve never seen before – from construction workers with core body temperatures of 107 degrees to elderly people found unconscious in their homes without air conditioning. An estimated 1,300 excess deaths occurred annually, on average, during extreme summer heat from 1975 to 2004. And more than 65,000 people, on average, end up in emergency rooms each summer with heat-related illnesses. The human cost is staggering, but so is the economic impact on an already strained healthcare system.
The Economic Toll Reaches Crisis Proportions
The impacts of extreme heat cost our Nation an estimated $162 billion in 2024 – equivalent to nearly 1% of the U.S. GDP. The impacts of extreme heat cost our Nation an estimated $162 billion in 2024 – equivalent to nearly 1% of the U.S. GDP. This staggering figure represents more than just economic damage – it’s a measure of human suffering translated into dollars. This past summer saw days when more than 100 million Americans were under a heat advisory. That means that there were days when it was too hot for a third of our country to safely work or play. The economic ripple effects cascade through agriculture, construction, transportation, and energy sectors. Workers can’t perform their jobs safely, crops fail, and power grids strain under the demand for cooling.
Medical Experts Sound the Alarm on Future Projections
The medical community is issuing increasingly urgent warnings about what’s coming next. “There’s just very low awareness that heat kills. It’s the silent killer,” said University of Washington public health scientist Kristie Ebi, who helped write a United Nations special report on extreme weather. Ebi said in the last few years, the heat “seems like it’s coming faster. It seems like it’s more severe than we expected.” Climate projections paint an even grimmer picture for the future. For instance, large urban areas such as New York, Philadelphia, Chicago, and Boston could each experience at least six times as many dangerously hot summer days by 2100 as they did, on average, from 1975 to 2010. Collectively, 45 major urban areas in the United States could see about 28,000 more deaths each year due to extremely hot summer days by the 2090s. These aren’t distant threats – they’re the reality our children will inherit.
The Fight Back Begins with Recognition and Action
Despite the overwhelming challenges, communities and governments are beginning to fight back with increasing urgency and innovation. Heat kills more Americans every year than hurricanes, floods, and tornadoes combined. Heat kills more Americans every year than hurricanes, floods, and tornadoes combined. This recognition is finally spurring action at multiple levels. Cities are creating cooling centers, implementing heat warning systems, and redesigning urban spaces to reduce heat islands. For example, local governments might combine heat and air pollution alert systems to convey that the exposures are related, and notify people to exercise increased caution when the two extremes coincide. To help people stay safe, communities can provide air-conditioned cooling centers for older adults and other sensitive groups. Long-term investments could include adding more green space, as well as pavement and rooftops built from reflective materials, to help reduce temperatures in urban heat islands. The deadly duo of heat and pollution has revealed our vulnerability, but it’s also catalyzing unprecedented cooperation between health departments, emergency management, and environmental agencies. What started as a crisis might just become the catalyst for the most comprehensive public health response to climate change in American history.
