As global temperatures rise, the U.S. faces a surge in heat-related deaths by mid-century, with older adults and ethnic minorities most at risk. Without swift climate action, the death toll could more than double.
Study: Projections of Extreme Temperature–Related Deaths in the US. Image Credit: VladisChern / Shutterstock.com
In a recent study published in JAMA Network Open, researchers analyze the current burden of mortality related to extreme temperatures in the United States. The researchers also estimate projected excess deaths due to rising temperatures in the next few decades based on demographic factors and emission trajectories of two greenhouse gases (GHGs).
How does extreme weather affect human health?
The exponential increase in GHG emissions due to human actions has led to extreme heat events in the U.S. that are expected to rise in the near future, whereas extreme cold events are reducing in frequency. Understanding the impact of these changes and shifts in population demographics on temperature-associated mortality is essential for shaping public health and climate change policies.
The human body functions optimally within a narrow temperature range; therefore, extreme heat or cold exposure can increase mortality risks. Several studies have reported that older adults and non-Hispanic Black individuals are particularly vulnerable to extreme temperatures.
Given the aging population and warming climate, more areas in the U.S. are expected to experience extreme heat for longer periods and have an increased burden of temperature-related mortality.
About the study
In the present study, researchers measure the burden of mortality associated with increased temperatures between 2008 and 2019.
Mortality data for adults 18 years of age and older was obtained from the National Center for Health Statistics, which also included information on sex, age, race and ethnicity, and county of death. GridMET datasets were used to obtain temperature data between 2008 and 2019. Data on sex, age, race, and ethnicity were adjusted for various socioeconomic scenarios for the county-level projections of population demographics.
A dataset that used 20 global climate models to simulate future temperatures was used for projected temperature data between 2035 and 2065. Under two different scenarios, the researchers estimated the projected burden of extreme temperature-associated deaths. In the first scenario, GHG emissions were reduced to moderate levels due to climate change policies, whereas continued fossil fuel use led to high emissions in the second scenario.
Regression modeling accounted for economic, environmental, demographic, and healthcare-associated factors while determining the association between increasing temperatures and mortality rates. Mortality estimates were calculated separately for individuals between 18 and 64 and those 65 and older based on age-related vulnerability to extreme temperatures.
Excess death was calculated by comparing observed deaths with estimated deaths that would have occurred if no extreme temperature days had occurred. These estimates were calculated for the present period and then projected for 2035-2065.
Study findings
Between 2008 and 2019, the annual average number of days in which temperatures were extremely high was 13.3, whereas the annual mean number of cold days was 8.2. The projections for the next few decades into the mid-21st century suggested a significant increase in temperatures, with an average of 40.7 extreme heat days every year if the GHG emissions were moderate.
If GHG emissions remained high due to the continued use of fossil fuels, the annual mean number of hot days between 2035 and 2065 was projected to be 52.1. The average number of cold days every year was expected to decrease from the current estimate of 8.2 to 3.2 and 2.6 in the intermediate and high GHG emission scenarios, respectively.
The baseline period data estimated 30.9 million deaths due to extreme temperatures, with mortality rates for men and women equivalent. However, mortality rates varied based on race and ethnicity, with individuals who were non-Hispanic White most affected, followed by individuals of non-Hispanic Black and Hispanic races.
Each additional day of extreme heat per month was estimated to increase mortality rates by 0.09% and 0.17% among adults 65 years of age and older and those between 18 and 64 years of age, respectively.
Extreme heat-related deaths were also expected to increase by the mid-21st century, with 15,641 and 22,936 deaths predicted yearly under the intermediate and high GHG emissions scenario, respectively, reflecting a 134.6% and 222.2% increase, respectively.
Older adults and those belonging to Hispanic and non-Hispanic Black populations were reported to be highly vulnerable to rising temperatures. Metropolitan residents were also expected to be at an increased risk of heat-related deaths than those living in rural areas.
Conclusions
The current study predicts a significant rise in temperatures and extreme temperature-related deaths in the U.S. by the mid-21st century. Older adults and those of non-Hispanic Black and Hispanic ethnicities are expected to be at a greater risk of heat-related mortality. These results emphasize the crucial need for effective adaptation and climate change policies to mitigate this risk.