Heatwaves are becoming more frequent and extending across longer seasons in the 50 major U.S. cities tracked by the EPA. Their measured health burden ranges from coded death-certificate counts in the United States to model-based global estimates, and these measures are not interchangeable.
Key Heatwave Statistics
The most broadly useful heatwave statistics include:
- U.S. cities averaged 2 heatwaves per year in the 1960s across the EPA’s 50-city indicator.
- U.S. cities averaged 6.1 heatwaves per year in the 2010s across the same 50-city indicator.
- The average heatwave season lasted 23 days in the 1960s in the 50 major U.S. cities.
- The average heatwave season lasted 70 days in the 2010s in those 50 cities.
- The EPA’s 2020s comparison puts the average season about 46 days longer than in the 1960s for the 50-city indicator.
- The recent average heatwave is about one day longer than the 1960s average in the EPA comparison of the 50 major U.S. cities.
- The United States recorded 10,527 heat-related deaths from 2004 through 2018 among residents in CDC death-certificate records.
- The annual U.S. average was 702 heat-related deaths from 2004 through 2018 when underlying and contributing causes were included.
- People aged 65 and older accounted for 4,019 U.S. heat-related deaths from 2004 through 2018, or 39% of decedents with known age.
- Males accounted for about 70% of U.S. heat-related deaths from 2004 through 2018 in the CDC series.
- The heat-related death rate for U.S. residents aged 65 and older was 0.7 per 100,000 from 2004 through 2018, the highest age-group rate reported.
- The United States recorded 3,340 heat-related deaths from 2006 through 2010, at a rate of 2.1 per million.
- U.S. people aged 85 and older had 332 heat-related deaths from 2006 through 2010, at 12.8 per million.
- The 2023 global heatwave estimate was 178,486 excess deaths, with a 95% empirical confidence interval of 159,892–204,147.
- The estimated 2023 global heatwave mortality rate was 23 deaths per million people.
- Southern Europe had an estimated 2023 heatwave mortality rate of 120 deaths per million, with a reported 95% interval of 116–126.
- Human-induced climate change was estimated to account for 54.29% of 2023 global heatwave-related deaths, with a 95% interval of 45.71%–61.36%.
- Asia accounted for an estimated 85,611 global heatwave excess deaths in 2023, or 47.97% of the model-based total.
Contents
- Key Heatwave Statistics
- Heatwave Frequency and Season-Length Trends in U.S. Cities
- Heatwave Duration and Intensity Data
- U.S. Heatwave Mortality Statistics
- Age, Sex, Race and Socioeconomic Heatwave Patterns
- Global Heatwave Mortality and Climate Attribution
- Heatwave Death Rates by Place, Urbanization and Cause
Heatwave Frequency and Season-Length Trends in U.S. Cities
The EPA/NOAA indicator covers 50 major U.S. cities, not every U.S. location. It defines a heatwave as at least two consecutive days above each city’s 85th percentile of historical July–August apparent minimum temperatures, using a 1981–2010 baseline.
| Period | Average heatwaves per year | Average season length |
|---|---|---|
| 1960s | 2 | 23 days |
| 1980s | 3.2 | 38 days |
| 2000s | 4.6 | 52 days |
| 2010s | 6.1 | 70 days |
| 2020s summary | 6 | Not supplied |
The EPA comparison shows frequency rising from 2 events per year in the 1960s to 3.2 in the 1980s, 4.6 in the 2000s and 6.1 in the 2010s. Its rounded 2020s comparison is 6 events per year, although the decade may be incomplete.
The average season expanded from 23 days in the 1960s to 38 days in the 1980s, 52 days in the 2000s and 70 days in the 2010s. In the EPA’s 2020s comparison, the season is about 46 days longer than in the 1960s; this does not mean the total number of heatwave days equals the season length.
Source: Climate Change Indicators in the United States, Fifth Edition. These are city-indicator results and should not be generalized to rural areas or all U.S. locations.
Heatwave Duration and Intensity Data
The EPA series indicates that the recent average heatwave is about one day longer than the 1960s average for the 50-city comparison. Event duration here means the length of an event under the EPA threshold definition, not the number of days in the full heatwave season.
The same indicator reports that heatwaves have become hotter on average in the 2010s and 2020s than in the 1960s. The summary reports the direction of the apparent-temperature change rather than one pooled temperature value.
The threshold itself is city-specific: each city uses the 85th percentile of historical July–August apparent minimum temperatures. That definition matters when comparing the trend across cities because the threshold is relative to each city’s 1981–2010 baseline.
Source: Climate Change Indicators in the United States, Fifth Edition. The indicator’s duration and intensity findings should be read within that definition and geography.
U.S. Heatwave Mortality Statistics
CDC death-certificate records counted 10,527 heat-related deaths among U.S. residents from 2004 through 2018. The annual average was 702 deaths when heat was listed as either the underlying or a contributing cause.
| Measure, 2004–2018 | Count or rate | Scope |
|---|---|---|
| Total heat-related deaths | 10,527 | U.S. residents |
| Annual average | 702 per year | U.S. residents |
| Heat as underlying cause | 6,220; 59% | U.S. residents |
| Heat as contributing cause | 4,307; 41% | U.S. residents |
| May–September share | About 90% | U.S. residents |
An average of 415 deaths per year listed heat as the underlying cause, while an average of 287 listed heat as a contributing cause. About 90% of the deaths occurred from May through September, but these are coded heat-related deaths rather than deaths necessarily occurring during officially named heatwaves.
Arizona, California and Texas accounted for 3,852 deaths, or 37% of the U.S. total, although the three states represented approximately 23% of the population in the report’s comparison. CDC notes that death certificates can undercount deaths when heat is not recorded.
Among contributing-cause deaths, major cardiovascular diseases were the underlying cause in 2,112 cases, or 49% of the 4,307-death subset. External causes were the underlying cause in 1,543 cases, or 36%; natural heat also contributed to 1,463 ischemic-heart-disease deaths, 438 hypertension deaths and 773 combined alcohol-poisoning and drug-overdose deaths.
Source: Heat-Related Deaths — United States, 2004–2018. The source uses natural-heat ICD codes and distinguishes underlying from contributing causes.
Age, Sex, Race and Socioeconomic Heatwave Patterns
The earlier NCHS series counted 3,340 U.S. heat-related deaths from 2006 through 2010, with a rate of 2.1 per million. Its age-specific results show a much higher rate among the oldest age groups.
| Group, 2006–2010 | Deaths | Rate |
|---|---|---|
| Age 85 and older | 332 | 12.8 per million |
| Age 75–84 | 490 | 7.5 per million |
| Age 65–74 | 463 | 4.5 per million |
| Males | 2,303 | 3.1 per million |
| Females | 1,029 | 1.2 per million |
| Non-Hispanic White | 2,067 | 1.8 per million |
People aged 85 and older had 332 deaths at 12.8 per million, while people aged 75–84 had 490 deaths at 7.5 per million and people aged 65–74 had 463 deaths at 4.5 per million. The same tables recorded 2,303 male deaths at 3.1 per million and 1,029 female deaths at 1.2 per million.
County income also varied across the reported groups. Counties with median household income of $49,241 or more recorded 1,658 deaths at 1.8 per million, while counties in the $36,518–$42,407 group recorded 554 deaths at 3.1 per million.
These income measures describe county median household income quartiles, not individual income. The race and ethnicity categories likewise follow the reporting systems used by NCHS and NVSS rather than a universal classification.
Source: Deaths Attributed to Heat, Cold, and Other Weather Events in the United States, 2006–2010.
Global Heatwave Mortality and Climate Attribution
Global heatwave figures use models rather than a direct worldwide death count. For 2023, one peer-reviewed estimate found 178,486 excess deaths, with a 95% empirical confidence interval of 159,892–204,147; this equaled 0.73% of global deaths and 23 deaths per million people.
| Region, 2023 | Estimated excess deaths | Share or rate |
|---|---|---|
| Asia | 85,611 | 47.97% of global total |
| Europe | 66,443 | 37.23% |
| Americas | 23,467 | 13.15% |
| Africa | 2,881 | 1.61% |
| Oceania | 83 | 0.05% |
Regional rates differed substantially: Southern Europe was estimated at 120 deaths per million, Eastern Europe at 107 and Western Europe at 66. The reported 95% intervals were 116–126 for Southern Europe, 100–114 for Eastern Europe and 62–70 for Western Europe.
The model estimated that human-induced climate change accounted for 54.29% of 2023 global heatwave-related deaths, with a 95% interval of 45.71%–61.36%. A separate multi-country study estimated that 37.0% of warm-season heat-related deaths were attributable to human-induced climate change, with country-level estimates ranging from 20.5% to 76.3%.
Another three-stage modelling study covering 1990–2019 reported a 13.9% reduction per decade relative to its 30-year average. That is a modelled burden trend, not a simple observed death-count series.
Sources: Global excess deaths associated with heatwaves in 2023 and the contribution of human-induced climate change, The burden of heat-related mortality attributable to recent human-induced climate change, and Global, regional, and national burden of heatwave-related mortality from 1990 to 2019: A three-stage modelling study. Estimates include uncertainty intervals and counterfactual assumptions.
Heatwave Death Rates by Place, Urbanization and Cause
The 2006–2010 NCHS data also show how heat-related mortality differed by region and urbanization category. These small-area results should be interpreted cautiously, especially where the death count is low.
| Place and category, 2006–2010 | Deaths | Rate |
|---|---|---|
| Western large central metropolitan counties | 649 | 4.0 per million |
| Western micropolitan counties | 43 | 1.7 per million |
| Western noncore nonmetropolitan counties | 40 | 3.0 per million |
Across all weather-related deaths in the United States during 2006–2010, the total was 10,649, including 3,340 heat-related deaths. The all-weather figure also includes cold, flood, storm and lightning deaths.
Heat-related mortality was 2.1 per million during this period, compared with 4.2 per million for excessive natural cold. Heat and cold were defined with separate ICD-10 categories, so the comparison describes two coded mortality measures rather than all deaths occurring during hot or cold weather.
The place-of-occurrence results do not establish that urbanization itself caused the differences. They are descriptive statistics for the NCHS categories and period reported.
Source: Deaths Attributed to Heat, Cold, and Other Weather Events in the United States, 2006–2010.