Climate Change Indicators in the United States: Heat-Related Deaths
www.epa.gov/climate-indicators - Updated August 2016
Heat-Related Deaths
This indicator presents data on deaths classified as "heat-related" in the United States.
Background
When people are exposed to extreme heat, they can suffer from potentially deadly illnesses, such as
heat exhaustion and heat stroke. Hot temperatures can also contribute to deaths from heart attacks,
strokes, and other forms of cardiovascular disease. Heat is the leading weather-related killer in the
United States, even though most heat-related deaths are preventable through outreach and
intervention (see EPA's Excessive Heat Events Guidebook at: www.epa.gov/heat-islands/excessive-heat-
events-guidebook).
Unusually hot summer temperatures have become more common across the contiguous 48 states in
recent decades1 (see the High and Low Temperatures indicator), and extreme heat events (heat waves)
are expected to become longer, more frequent, and more intense in the future.2 As a result, the risk of
heat-related deaths and illness is also expected to increase.3 Reductions in cold-related deaths are
projected to be smaller than increases in heat-related deaths in most regions.4 Death rates can also
change, however, as people acclimate to higher temperatures and as communities strengthen their heat
response plans and take other steps to continue to adapt.
Certain population groups already face higher risks of heat-related death, and increases in summertime
temperature variability will increase that risk.5,6 The population of adults aged 65 and older, which is
expected to continue to grow, has a higher-than-average risk of heat-related death. Children are
particularly vulnerable to heat-related illness and death, as their bodies are less able to adapt to heat
than adults, and they must rely on others to help keep them safe.7 People with certain diseases, such as
cardiovascular and respiratory illnesses, are especially vulnerable to excessive heat exposure, as are the
economically disadvantaged. Data also suggest a higher risk among non-Hispanic blacks.8
About the Indicator
This indicator shows the annual rate for deaths classified by medical professionals as "heat-related" in
the United States based on death certificate records. Every death is recorded on a death certificate,
where a medical professional identifies the main cause of death (also known as the underlying cause),
along with other conditions that contributed to the death. These causes are classified using a set of
standard codes. Dividing the annual number of deaths by the U.S. population in that year, then
multiplying by one million, will result in the death rates (per million people) that this indicator shows.
Figure 1 shows heat-related death rates using two methods. One method shows deaths for which
excessive natural heat was stated as the underlying cause of death from 1979 to 2014. The other data
series shows deaths for which heat was listed as either the underlying cause or a contributing cause,
based on a broader set of data that, at present, can only be evaluated back to 1999. For example, in a
case where cardiovascular disease was determined to be the underlying cause of death, heat could be
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Climate Change Indicators in the United States: Heat-Related Deaths
www.epa.gov/climate-indicators - Updated August 2016
listed as a contributing factor because it can make the individual more susceptible to the effects of this
disease. Because excessive heat events are associated with summer months, the 1999-2014 analysis
was limited to May through September.
Figure 2 offers a closer look at cardiovascular disease deaths for which heat was recorded as a
contributing cause. This graph includes deaths due to heart attacks, strokes, and other diseases related
to the circulatory system. Figure 2 shows death rates for the overall population as well as two groups
with a higher risk: people age 65 and older and non-Hispanic blacks. Like the "underlying and
contributing causes" analysis in Figure 1, Figure 2 is restricted to the summer months, and it uses data
that are available from 1999 to 2014.
Key Points
• Between 1979 and 2014, the death rate as a direct result of exposure to heat (underlying cause
of death) generally hovered around 0.5 to 1 deaths per million people, with spikes in certain
years (see Figure 1). Overall, a total of more than 9,000 Americans have died from heat-related
causes since 1979, according to death certificates.
• For years in which the two records overlap (1999-2014), accounting for those additional deaths
in which heat was listed as a contributing factor results in a higher death rate—nearly double for
some years—compared with the estimate that only includes deaths where heat was listed as the
underlying cause (see Figure 1).
• The indicator shows a peak in heat-related deaths in 2006, a year that was associated with
widespread heat waves and was one of the hottest years on record in the contiguous 48 states
(see the U.S. and Global Temperature indicator).
• The death rate from heat-related cardiovascular disease ranged from 0.08 deaths per million
people in 2004 to 1.08 deaths per million people in 1999 (see Figure 2). Overall, the interaction
of heat and cardiovascular disease caused about one-fourth of the heat-related deaths recorded
in the "underlying and contributing causes" analysis since 1999 (see Figures 1 and 2).
• Since 1999, people aged 65+ have been several times more likely to die from heat-related
cardiovascular disease than the general population, while non-Hispanic blacks generally have
had higher-than-average rates (see Figure 2).
• Examination of extreme events has revealed challenges in capturing the full extent of "heat-
related" deaths. For example, studies of the 1995 heat wave event in Chicago (see example
figure) suggest that there may have been hundreds more deaths than were actually reported as
"heat-related" on death certificates.
• While dramatic increases in heat-related deaths are closely associated with the occurrence of
hot temperatures and heat waves, these deaths may not be reported as "heat-related" on death
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Climate Change Indicators in the United States: Heat-Related Deaths
www.epa.gov/climate-indicators - Updated August 2016
certificates. This limitation, as well as considerable year-to-year variability in the data, make it
difficult to determine whether the United States has experienced a meaningful increase or
decrease in deaths classified as "heat-related" overtime.
Figure 1. Deaths Classified as "Heat-Related" in the United States, 1979-2014
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Climate Change Indicators in the United States: Heat-Related Deaths
www.epa.gov/climate-indicators - Updated August 2016
Figure 2. Summer Deaths Due to Heat and Cardiovascular Disease in the United States, 1999-
2014
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This figure shows rates for deaths that medical professionals have classified as being caused by a
combination of cardiovascular disease (diseases of the circulatory system) and heat exposure. This graph
presents summer (May to September) death rates from 1999 to 2014 for three population groups in the
50 states arid the District of Columbia, The purple line shows rates for the entire population, the green
line shows rates for non-Hispanic black people, and the pink line shows rates for people aged 65 and
older.
Data source: CDC, 20161
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Climate Change Indicators in the United States: Heat-Related Deaths
www.epa.gov/climate-indicators - Updated August 2016
Example: Examining Heat-Related Deaths During the 1995 Chicago Heat Wave*
Cook County, July 11-27,1995:
Excess deaths compared with this time period during an average year: about 700
Deaths classified as "heat-related" on death certificates (not shown here): 465
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Climate Change Indicators in the United States: Heat-Related Deaths
www.epa.gov/climate-indicators - Updated August 2016
are not identified as such by the medical examiner and might not be correctly coded on the death
certificate. In many cases, the medical examiner might classify the cause of death as a cardiovascular or
respiratory disease, not knowing for certain whether heat was a contributing factor, particularly if the
death did not occur during a well-publicized heat wave. Furthermore, deaths can occur from exposure
to heat (either as an underlying cause or as a contributing factor) that is not classified as extreme and
therefore is often not recorded as such. Some statistical approaches estimate that more than 1,300
deaths per year in the United States are due to extreme heat, compared with about 600 deaths per year
in the "underlying and contributing causes" data set shown in Figure l.17 By studying how daily death
rates vary with temperature in selected cities, scientists have found that extreme heat contributes to far
more deaths than the official death certificates might suggest.18 This is because the stress of a hot day
can increase the chance of dying from a heart attack, other heart conditions, or respiratory diseases
such as pneumonia.19 These causes of death are much more common than heat-related illnesses such as
heat stroke. Thus, this indicator very likely underestimates the number of deaths caused by exposure to
heat.
Classifying a death as "heat-related" does not mean that high temperatures were the only factor that
caused or contributed to the death, as pre-existing medical conditions can significantly increase an
individual's susceptibility to heat. Other important factors, such as the overall vulnerability of the
population, the extent to which people have adapted and acclimated to higher temperatures, and the
local climate and topography, can affect trends in heat-related deaths. Heat response measures, such as
early warning and surveillance systems, air conditioning, health care, public education, cooling centers,
infrastructure standards, and air quality management, can also make a big difference in reducing death
rates. For example, after a 1995 heat wave, the city of Milwaukee developed a plan for responding to
extreme heat conditions; during a 1999 heat wave, heat-related deaths were roughly half of what would
have been expected.20
Future development related to this indicator should focus on capturing all heat-related deaths, not just
those with a reported link to heat stress.
Data Sources
Data for this indicator were provided by the U.S. Centers for Disease Control and Prevention (CDC). The
1979-2014 underlying cause data in Figure 1 are publicly available through the CDC WONDER database
at: http://wonder.cdc.gov/mortSQL.html. The 1999-2014 analysis in Figure 1 was developed by CDC's
Environmental Public Health Tracking Program, which provides a summary at:
www.cdc.gov/nceh/tracking. The cardiovascular disease data in Figure 2 are publicly available through
the CDC WONDER database at: http://wonder.cdc.gov/mcd-icdlO.html.
1 Melillo, J.M., T.C. Richmond, and G.W. Yohe (eds.). 2014. Climate change impacts in the United States: The third
National Climate Assessment. U.S. Global Change Research Program, http://nca2014.globalchange.gov.
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Climate Change Indicators in the United States: Heat-Related Deaths
www.epa.gov/climate-indicators - Updated August 2016
2 Melillo, J.M., T.C. Richmond, and G.W. Yohe (eds.). 2014. Climate change impacts in the United States: The third
National Climate Assessment. U.S. Global Change Research Program, http://nca2014.globalchange.gov.
3 IPCC (Intergovernmental Panel on Climate Change). 2014. Climate change 2014: Impacts, adaptation, and
vulnerability. Working Group II contribution to the IPCC Fifth Assessment Report. Cambridge, United Kingdom:
Cambridge University Press, www.ipcc.ch/report/ar5/wg2.
4 Sarofim, M.C., S. Saha, M.D. Hawkins, D.M. Mills, J. Hess, R. Horton, P. Kinney, J. Schwartz, and A. St. Juliana.
2016. Chapter 2: Temperature-related death and illness. The impacts of climate change on human health in the
United States: A scientific assessment. U.S. Global Change Research Program.
https://health2016.globalchange.gov.
5 Zanobetti, A., M.S. O'Neill, C.J. Gronlund, and J.D. Schwartz. 2012. Summer temperature variability and long-
term survival among elderly people with chronic disease. P Natl. Acad. Sci. USA 109(17):6608-6613.
6 Sarofim, M.C., S. Saha, M.D. Hawkins, D.M. Mills, J. Hess, R. Horton, P. Kinney, J. Schwartz, and A. St. Juliana.
2016. Chapter 2: Temperature-related death and illness. The impacts of climate change on human health in the
United States: A scientific assessment. U.S. Global Change Research Program.
https://health2016.globalchange.gov.
7 USGCRP, 2016: The Impacts of Climate Change on Human Health in the United States: A Scientific Assessment.
Crimmins, A., J. Balbus, J.L. Gamble, C.B. Beard, J.E. Bell, D. Dodgen, R.J. Eisen, N. Fann, M.D. Hawkins, S.C.
Herring, L Jantarasami, D.M. Mills, S. Saha, M.C. Sarofim, J. Trtanj, and L Ziska, Eds. U.S. Global Change
Research Program, Washington, DC, 312 pp. http://dx.doi.org/10.7930/J0R49NQX
8 Berko, J., D.D. Ingram, S. Saha, and J.D. Parker. 2014. Deaths attributed to heat, cold, and other weather events
in the United States, 2006-2010. National Health Statistics Reports, Number 76. National Center for Health
Statistics, www.cdc.gov/nchs/data/nhsr/nhsr076.pdf.
9 CDC (U.S. Centers for Disease Control and Prevention). 2016. CDC WONDER database: Compressed mortality
file, underlying cause of death. Accessed February 2016. http://wonder.cdc.gov/mortSQL.html.
10 CDC (U.S. Centers for Disease Control and Prevention). 2016. Indicator: Heat-related mortality. National Center
for Health Statistics. Annual national totals provided by National Center for Environmental Health staff in June
2016. http://ephtracking.cdc.gov/showlndicatorPages.action.
11 CDC (U.S. Centers for Disease Control and Prevention). 2016. CDC WONDER database: Multiple cause of death
file. Accessed July 2016. http://wonder.cdc.gov/mcd-icd 10.html.
12 Anderson, G.B., and M.L. Bell. 2011. Heat waves in the United States: Mortality risk during heat waves and effect
modification by heat wave characteristics in 43 U.S. communities. Environ. Health Persp. 119(2):210-218.
13 CDC (U.S. Centers for Disease Control and Prevention). 1995. Heat-related mortality—Chicago, July 1995.
Morbidity and Mortality Weekly Report 44(31):577-579.
14 NRC (National Research Council). 2011. Climate stabilization targets: Emissions, concentrations, and impacts
over decades to millennia. Washington, D.C.: National Academies Press.
15 CDC (U.S. Centers for Disease Control and Prevention). 2012. CDC WONDER database. Accessed August 2012.
http://wonder.cdc.gov/mortSQL.html.
16 NOAA (National Oceanic and Atmospheric Administration). 2012. National Centers for Environmental
Information. Accessed August 2012. www.ncdc.noaa.gov.
17 Sarofim, M.C., S. Saha, M.D. Hawkins, D.M. Mills, J. Hess, R. Horton, P. Kinney, J. Schwartz, and A. St. Juliana.
2016. Chapter 2: Temperature-related death and illness. The impacts of climate change on human health in the
United States: A scientific assessment. U.S. Global Change Research Program.
https://health2016.globalchange.gov.
18 Medina-Ramon, M., and J. Schwartz. 2007. Temperature, temperature extremes, and mortality: A study of
acclimatization and effect modification in 50 U.S. cities. Occup. Environ. Med. 64(12):827-833.
19 Kaiser, R., A. Le Tertre, J. Schwartz, C.A. Gotway, W.R. Daley, and C.H. Rubin. 2007. The effect of the 1995 heat
wave in Chicago on all-cause and cause-specific mortality. Am. J. Public Health 97(Supplement 1):S158-S162.
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Climate Change Indicators in the United States: Heat-Related Deaths
www.epa.gov/climate-indicators - Updated August 2016
20 Weisskopf, M.G., H.A. Anderson, S. Foldy, L.P. Hanrahan, K. Blair, T.J. Torok, and P.D. Rumm. 2002. Heat wave
morbidity and mortality, Milwaukee, Wis., 1999 vs. 1995: An improved response? Am. J. Public Health 92:830-
833.
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