Climate Change Is Subjecting More Americans to Unbearable Extreme Heat

The start of summer 2025 brought a massive heat dome over the United States, subjecting more than 255 million Americans to what meteorologists called “dangerous, life-threatening” conditions of triple-digit temperatures and high humidity.¹ Spiking summer temperatures as a result of fossil-fueled climate change could mean that Americans have already experienced the coolest summer of their lifetime—and have yet to experience the hottest.²

All 10 of the warmest years on record occurred between 2014 and 2023, until 2024 shattered global heat records and became the hottest year yet.³ In July 2024, the world experienced its hottest day ever, with numerous cities across 35 states breaking their daily heat records in the span of only two months.⁴ Record highs occur twice as often as record lows across the continental United States, while the average rate of heat waves in the United States has tripled since the 1960s.⁵

Today, extreme heat is the nation’s deadliest weather-related threat,⁶ straining hospitals and power grids; endangering workers; and hitting older adults and low-income, Black, and brown communities the hardest.

These recent, more extreme heat waves are not normal.⁷ Scientists can differentiate between natural fluctuations in weather and abnormal climate patterns by examining glaciers, ocean sediments, tree rings, and even pollen remains, as well as ice cores from the Earth’s polar regions, which reveal the planet’s conditions 800,000 years back.⁸ The composition of the results from these studies overwhelmingly show that the greenhouse gas carbon dioxide’s levels are 50 percent higher today than they were in the 19th century, before the industrial revolution.⁹

The use of fossil fuels for industries including transportation, energy generation, manufacturing, and agriculture is driving this increase in carbon dioxide levels, resulting in long-term global warming.¹⁰ While heat waves are a natural phenomenon,¹¹ fossil-fueled climate change makes them more frequent and more prolonged today than they were in the 20th century.¹² Average global temperatures have increased faster in the past several decades than at any time in at least the past 2,000 years.¹³ By 2060, average temperatures in more than 240 major U.S. cities are projected to rise by 3.6 degrees Fahrenheit,¹⁴ making summers in places such as Casper, Wyoming,¹⁵ and Billings, Montana,¹⁶ feel more like today’s summers in Albuquerque, New Mexico. And by 2100, cities such as Austin, Texas,¹⁷ could experience summer heat comparable to Dubai.

Extreme heat is the deadliest form of extreme weather¹⁸ and, in most years, kills more Americans than floods, tornadoes, and hurricanes combined.¹⁹ More than 21,000 deaths in the United States from 1999 to 2023 were recorded as being related to heat,²⁰ with mortality rates starting to increase the most from 2016 onward. Although some states experience extreme heat more frequently than others, nearly 210 million Americans live in counties vulnerable to health threats from unexpectedly high summer temperatures.²¹ Look no further than the June 2025 heat dome, which subjected more than 255 million Americans to extreme heat, for evidence of the health threats posed by extreme heat waves.²² This heat wave was potentially the cause of death for a woman in St. Ann, Missouri, with an underlying health condition who had her air conditioning (AC) cut off while St. Louis was under a heat advisory in late June 2025. Residents in the St. Louis area experience an average of more than nine extreme heat days in the summer, according to the Natural Resources Defense Council’s analysis, which also found that millions more Americans today are living in areas with more than nine extreme heat days per summer than in the early 2000s.²³ Extreme heat will continue to threaten public health and is projected to lead to a cumulative total of about 28,000 more deaths in major U.S. urban areas each year by the 2090s.²⁴

Even though the threat of heat-related illness and death is growing, these deaths and illnesses remain dangerously undercounted.²⁵ Extreme heat compromises the body’s ability to regulate temperature and can cause a person to suffer from heat stroke, exhaustion, or dehydration.²⁶ However, a physician might not recognize these illnesses as being heat related or assign them the proper diagnostic code.²⁷ Patients with chronic diseases are more vulnerable to extreme heat and can experience physical complications that worsen their condition, but diagnostic codes might omit mention of heat-related illness and instead focus on the clinical exacerbations of the underlying illness.²⁸

More frequent extreme heat hits working-class and low-income Americans the hardest

Extreme heat can be deadly and cause illness in anyone, but it is disproportionately severe for vulnerable Americans.²⁹ Those who are most vulnerable to heat-related health effects include working-class, low-income, and majority Black or Latino communities, as well as people with disabilities and chronic illnesses, people who are pregnant, people who work or exercise outside, older adults, and young children.³⁰

The risk of heat-related illness and death is particularly high for those who lack AC or cannot afford to run it, and this risk is escalating with climate change.³¹ Of the 6.3 million U.S. households without AC, most are low income and in regions with above-average temperatures.³² Underserved communities have less access to AC and other heat reduction strategies and health resources, including equitable access to environmental amenities and green spaces. As a result, low-income neighborhoods can be as much as 12 degrees hotter during a heat wave than nearby wealthier neighborhoods and experience higher rates of extreme heat-related illness.³³

The risk of heat-related stress and death is far greater for farm workers than for all other U.S. civilian workers.³⁴ The same workers who are most exposed to extreme heat in industries such as construction, warehouses, and agriculture are disproportionately immigrants, Latino Americans, and low-wage earners. For example, 83 percent of U.S. farmworkers are Latino, and 75 percent are Latino migrants.³⁵ Americans with heightened sensitivity to heat also face greater health risks from high temperatures. Those with chronic illnesses may have trouble breathing, chest pain, and other medical complications.³⁶ Extreme heat exposure for people who are pregnant increases their risk of hospitalization, maternal mortality, near-fatal pregnancy complications, and severe maternal morbidity by 27 percent.³⁷ This risk is even higher for pregnant Black women, who are more likely to live in a concrete, heat-trapping “urban heat island”; less likely to have access to AC; and have double the risk of hospitalization, relative to white women, for every additional day they are exposed to extreme heat in their third trimester.³⁸

The oldest and youngest of Americans are also at high risk of extreme heat-related illness. As the human body ages, it becomes less efficient at adapting to extreme temperatures.⁴³ Americans ages 60 or older account for more than 80 percent of U.S. deaths from extreme heat.⁴⁴ An analysis found that Virginia ZIP codes with higher percentages of residents aged 65 or older had a 23 percent increased risk of heat-related hospitalizations and emergency room visits during heat events.⁴⁵ Meanwhile, young children who are smaller and still growing have a harder time thermoregulating.⁴⁶ Not only can their bodies heat up to five times faster than adults, but they are also more vulnerable to extreme heat since they play outdoors often and potentially spend more time in aging, inefficient school and child care infrastructure.⁴⁷ Extreme heat can worsen inequities in both health and educational outcomes for children, and it will pose a greater risk to their development than previous generations as fossil-fueled climate change exacerbates extreme weather conditions.⁴⁸

Frequent heat waves threaten U.S. farmlands and destabilize ecosystems

As heat waves become more frequent and intense, their effects on ecosystems and agriculture are becoming visible. One of the most alarming consequences of extreme heat is the rise of “megadroughts.”⁴⁹ Extreme heat can reduce soil moisture and lead to drier lands, less surface water, and greater stress on U.S. irrigation systems in the long term.⁵⁰ These conditions result in more extended droughts that reduce agricultural productivity.⁵¹ The western United States is in the midst of a megadrought that has persisted for decades and has been unprecedented for at least 1,200 years.⁵² Prolonged exposure to excessive heat can damage crops, injure or kill livestock, and increase risk of wildfires.⁵³ The Pacific Northwest’s June 2021 drought and heat wave led to more than $38.5 billion in damage as well as mass die-offs of fishery species vital to the region’s indigenous communities and economy.⁵⁴

Rising temperatures increase the spread of invasive species that outcompete native plants and animals; bring new diseases; and cause millions of dollars in economic losses to fishers, loggers, ranchers, and farmers who depend on the agricultural and marine industries.⁵⁵ As U.S. temperatures warm, some land animals are migrating north by an average of 3.8 miles per decade, and some marine species have shifted north by more than 17 miles per decade.⁵⁶ These changes cause reductions or extinctions of some populations, interrupt ecosystem interactions, and destabilize entire food webs that humans and other species depend on.⁵⁷

Extreme heat’s environmental impacts are not limited to land. On July 24, 2023, a buoy in Manatee Bay in the Florida Keys recorded a temperature of 101.1 degrees Fahrenheit, an alarmingly high sea surface temperature.⁵⁸ This marine heat wave caused coral reefs across the region to bleach, meaning they expelled the symbiotic algae that help them produce food and turned white.⁵⁹ Coral restoration projects throughout the Florida Keys were devastated, and the area lost 78 percent of its staghorn corals⁶⁰ and 95 percent of its elkhorn coral outplantings.⁶¹ Warming oceans, marine heat waves, and the resultant acidification are the greatest threats to coral reefs.⁶²

Losing coral reefs will have a devastating effect on coastal communities across the United States. Coral reefs support 81,300 jobs and $4.4 billion in reef-related expenditures in Florida alone.⁶³ Reefs are even more critical to the communities and economies of Hawaii and the five U.S. territories, where tourism is the largest industry.⁶⁴ Tourism represents 60 percent of Guam’s annual business revenue,⁶⁵ and coral reefs are the main attraction for the territory’s visitors, not to mention critically important to the culture of Native Chamorro people.⁶⁶ Without action, coral reefs—and the services they provide to people—could be lost by 2050.⁶⁷

Kelp forests are another type of marine habitat that provide recreational and tourism benefits to coastal communities.⁶⁸ Kelp are also threatened by climate change. Marine heat waves in the past decade were a major driver of the collapse of bull kelp forests in California.⁶⁹ Combined with overgrazing by purple sea urchins, these heat waves reduced the growth and survival rates of kelp.⁷⁰ These underwater rainforests are essential to communities across the United States for fisheries’ production, nutrient cycling, and carbon removal.⁷¹ Losing kelp threatens the livelihoods of commercial and recreational fishers up and down the West Coast and businesses that bring tourists to visit them. Visitors to California’s Channel Islands National Park in 2022 alone spent $21.8 million in communities near the park.⁷²

According to NASA, more than 90 percent of the heat trapped by greenhouse gases is absorbed by the ocean.⁷³ This threatens marine habitats important to coastal communities and economies. The ocean’s role in climate change cannot be overstated, as it is the largest habitat in the United States and holds massive amounts of carbon.

As extreme heat devastates communities and ecosystems, it also has a significant and far-reaching impact on the U.S. economy—disrupting industries; damaging infrastructure; and raising costs for households, businesses, and governments alike.

Rising health care costs

Higher temperatures lead to higher health care spending as more people seek medical attention for heat-related illnesses. Each summer, heat event days in the United States cause an estimated $1 billion in additional health care costs.⁷⁴ This includes $177.3 million in treat-and-release emergency department visits and $834.9 million in hospital admissions.⁷⁵ These costs are shared across society: Individuals and families face medical bills and lost wages,⁷⁶ employers absorb higher insurance premiums and productivity losses, and the government pays additional Medicare and Medicaid expenses.⁷⁷

Strain on infrastructure and energy systems

Extreme heat can significantly damage critical infrastructure, including roads, railways, bridges, and power grids.⁷⁸ Asphalt softens and can buckle in high temperatures creating road damage and safety hazards.⁷⁹ Similarly, metal railways expand in the heat, increasing the risk of buckled tracks and train derailments.⁸⁰ Bridges too are vulnerable, as expanding steel components can compromise structural integrity.⁸¹ Over the next two decades, rising temperatures are projected to add from $19 billion to $26.3 billion in additional road and maintenance costs nationwide, as many U.S. roadways were constructed with asphalt materials selected for cooler climate conditions.⁸²

Energy systems are similarly stressed by extreme heat waves. As temperatures rise, electricity demand spikes due to increased dependence on AC in homes and businesses.⁸³ This can drive up energy costs by as much as 22 percent for businesses and consumers alike.⁸⁴ At the same time, extreme heat reduces power generation efficiency,⁸⁵ lowers transmission capacity,⁸⁶ and can cause transformers to overheat and fail.⁸⁷ These combined pressures strain the grid and increase the risk of rolling power outages during heat waves.⁸⁸

These infrastructure and energy disruptions carry widespread economic consequences. Governments and taxpayers shoulder the cost of repairing public infrastructure, restoring power, providing emergency services, and operating cooling centers.⁸⁹ Meanwhile, businesses suffer lost revenue due to power outages, disrupted operations, fewer customers, and reduced workforce attendance and productivity.⁹⁰

Lost labor productivity

Extreme heat reduces work hours, increases absenteeism, and lowers worker output, especially in sectors requiring outdoor or manual labor.⁹¹ Once temperatures reach 90 degrees Fahrenheit, productivity can drop by 70 percent.⁹² A recent study estimates that heat-induced lost labor productivity costs the U.S. economy $100 billion annually, and the costs could reach $500 billion by 2050 due to climate change.⁹³ This impact is felt most acutely in heat-exposed and labor- intensive industries such as agriculture, manufacturing, construction, and service sectors with outdoor operations.⁹⁴

Threats to agriculture and the food supply

Agriculture is particularly vulnerable to extreme heat through heat’s direct impacts on crops and livestock and the labor disruptions it causes.⁹⁵ Many key crops including, corn, soy, and wheat—which represent 62 percent of U.S. farmland—are vulnerable to temperature.⁹⁶ Corn alone loses $720 million in revenue annually from heat-induced yield declines.⁹⁷ Since 2001, federal and private insurers have paid more than $1.3 billion in crop insurance claims for heat-related crop losses in the Southwest.⁹⁸ These agricultural disruptions increase food prices for families and individuals, and they threaten long-term food security.⁹⁹

As climate change accelerates, extreme heat will increasingly burden the U.S. economy. It will affect everything from the food on American tables to the reliability of infrastructure. Proactive adaptation and mitigation strategies are critical to reduce these mounting costs for families, businesses, and government.

Given the rising health risks and costs of longer, more intense, and more frequent extreme heat events driven by climate change, federal, state, and local leaders have begun to take action to protect Americans from dangerously hot temperatures. Some of these actions are described below:

• Leadership and planning for extreme heat: In 2024, the federal government released a “National Heat Strategy” to coordinate agency actions to protect communities from more extreme heat, including the planning, response, and actions necessary to keep Americans safe when temperatures spike.¹⁰⁰ However, the status of this strategy’s implementation is uncertain at this time.¹⁰¹ Several states including California, Arizona, New Jersey, and New York also have extreme heat plans.¹⁰² Arizona named a statewide chief heat officer, and New Jersey designated its chief resilience officer as the lead for heat planning and coordination across the state.¹⁰³ In addition, some cities and counties have appointed leads for their heat planning and response. For example, Miami-Dade County has a chief heat officer.¹⁰⁴
• Extreme heat worker protections: While the federal Occupational Safety and Health Act requires employers to ensure that working conditions are safe and free of known hazards that could seriously harm or kill workers, no specific federal law currently protects U.S. workers from extreme heat.¹⁰⁵ In 2024, the federal government proposed a rule that would have protected indoor and outdoor workers exposed to extreme heat health and safety risks. The Occupational Safety and Health Administration recently held a rulemaking hearing on the proposed rule. In the absence of federal action, seven states have enacted standards to protect workers from extreme heat, including California, Colorado, Maryland, Minnesota, Nevada, Oregon, and Washington state.¹⁰⁶ For example, California’s standards protect outdoor and indoor workers—including in the agriculture, construction, landscaping, and oil and gas extraction sectors—but exclude workers at correctional facilities, workers protecting life and property during emergencies, and remote employees working from home or other locations.¹⁰⁷ Nevada’s standards cover employers with more than 10 employees, excluding employers in the mining industry, and protect indoor and outdoor workers that are not in climate-controlled environments.¹⁰⁸ Both states’ standards require employers to provide workers with water, shade and cool-down breaks, emergency response procedures, heat illness prevention plans, and more.
• Rebates and tax credits for heat pump AC and energy efficiency improvements: The federal government and some states such as Maryland, Washington, Texas, Vermont, and New York offer low- and medium-income households rebates for efficient and cost-effective heat pump AC and other home efficiency upgrades to help families improve the health, safety, and livability of their homes during heat waves and other extreme weather events.¹⁰⁹ These rebates help alleviate the financial barrier that has prevented many households from securing access to efficient heat pump AC, heating, and other home energy improvements.¹¹⁰ The Inflation Reduction Act (IRA) provided $8.8 billion for home energy rebates, which California, New Mexico, Maine, Georgia, New York, and Washington, D.C., are using to support home efficiency upgrades for their residents, however, the future of this funding is uncertain.¹¹¹ In addition, the IRA provided energy-efficient home improvement credits (25C), offering homeowners up to $3,200 per year in tax credits to reduce the cost of home energy efficiency upgrades by up to 30 percent, including purchasing heat pumps. However, these credits were terminated by the One Big Beautiful Bill Act.¹¹² Federal and state leaders can also encourage households to make home envelope improvements—such as adding insulation and sealing, installing new windows, and repairing roofs—to further increase energy bill savings and help keep families safe, healthy, and comfortable year-round.¹¹³
• Lowering household energy costs: The federal Low Income Home Energy Assistance Program (LIHEAP) provides essential support for households that struggle to pay electricity bills.¹¹⁴ While this program offers a lifeline to families unable to cover their heating bills during cold months, funds often run out before or during the hot summer months, leaving many families without the support needed to cool their homes.¹¹⁵ Nonetheless, President Donald Trump has threatened to eliminate LIHEAP altogether in his proposed fiscal year 2026 budget.¹¹⁶ The U.S. Department of Energy’s Weatherization Assistance Program supports home weatherization and other improvements for roughly 32,000 homes every year, saving families an annual average of $372 or more.¹¹⁷ The U.S. Department of Housing and Urban Development’s (HUD) Green and Resilient Retrofit Program was designed to invest in energy efficiency and healthy affordable housing to help reduce energy and water bills and keep families living in HUD-assisted multifamily housing safe during extreme weather, including increasingly hotter heat waves.¹¹⁸ While this program improves the affordability and livability of housing for low-income Americans, the future of it is uncertain.¹¹⁹
• Expand clean energy investments to meet rising electricity demands and avoid power outages during extreme heat events: The U.S. electric grid is at a make-or-break moment. Demand is surging due to the growing artificial intelligence industry,¹²⁰ and the increased occurrence of extreme weather events, including heat waves, is only going to add even more pressure on the grid during those moments. Fortunately, clean energy creates a more reliable and balanced electric grid to address these issues¹²¹ and has proven to perform above expectations in extreme weather events.¹²² To avoid power outages and a failing grid during extreme heat waves, the United States must invest more money—not less—in clean energy. This includes expanding solar and wind to add more energy directly onto the grid, investing in sources such as batteries and geothermal to fill in when demand is high, and developing innovative technologies to advance the efficiency and reliability of existing energy sources such as nuclear power. Additionally, America needs to prioritize building an electric grid that can handle the growing electricity demand by expanding and upgrading interregional transmission capacity, investing in grid-enhancing technologies, and updating and streamlining grid interconnection processes.
• Tree planting to cool neighborhoods: The U.S Department of Agriculture’s Urban and Community Forestry Program helps states, cities, and other partners expand parks and tree canopies in communities, which can reduce extreme heat health risks and the urban heat island effect.¹²³ Maryland’s tree-planting initiative aims to plant and maintain 5 million native trees by 2031, focusing on underserved neighborhoods where tree cover is often sparse and extreme heat risks are high.¹²⁴ New York City reached its goal to plant 1 million trees to improve air quality, reduce storm runoff, and provide shade in underserved communities.¹²⁵ Other cities such as Austin, Texas; Atlanta, Georgia; Baltimore, Maryland; Chicago, Illinois; Los Angeles, California; Philadelphia, Pennsylvania; Portland, Oregon; San Francisco, California; and Washington, D.C., are also expanding tree cover and green spaces to reduce extreme heat and flood risks.¹²⁶ The Greening of Detroit, a nonprofit organization, has planted more than 166,000 trees to improve community health and provide jobs and job training for Detroiters.¹²⁷
• Cooling centers. Many large cities—including New York, Phoenix, and Washington, D.C.—open cooling centers during heat waves to keep residents who do not have access to AC safe.¹²⁸ While cooling centers offer residents shelter from the heat, they alone are insufficient to keep people safe, as many people are unaware of center locations or lack access to transportation needed to reach them.¹²⁹

Extreme heat is no longer a distant threat. It is a growing, scorching reality for most Americans, straining hospitals and infrastructure and endangering communities and ecosystems. As temperatures rise, so do the risks to children and older adults, jobs and the economy, and the health of all people—particularly the most vulnerable. Addressing this crisis requires bold climate action to curb fossil fuel emissions, paired with resilience efforts at the federal, state, and local levels to protect Americans from deadly heat.

The authors would like to thank the many individuals who shared their expertise or reviewed this report, including Trevor Higgins, Devon Lespier, Lucero Marquez, Leo Banks, Alia Hidayat, Kendra Hughes, Mariam Rashid, Alex Thornton, Jill Rosenthal, Beatrice Aronson, and Carl Chancellor.