Temperature-related deaths in the U.S. by 2065

A novel study shows a growing risk of heat-related mortality in the U.S. The number of deaths is expected to rise significantly by mid-century, with ethnic minorities and older people facing the greatest risk from climate change and rising greenhouse gas emissions.

Test: Projections of extreme heat-related deaths in the U.S.. Photo credit: Miguel AF/Shutterstock.com

In a recent study published in JAMA network openThe researchers examined the current burden of heat-related mortality in the continental United States (US) from 2008 to 2019. They also produced a projection of heat-related mortality in the mid-21st century, i.e. between 2036 and 2065.

In the United States (US), extreme heat has increased significantly due to anthropogenic greenhouse gas emissions, while extreme frigid has decreased. Understanding the impact of extreme temperatures and demographic changes on public health is crucial to developing strategies to prevent the health effects of climate change.

Identifying subgroups based on age, gender, race, ethnicity, or area of ​​residence may enable more targeted treatments to reduce adverse health outcomes.

About the study

In this cross-sectional study, researchers assessed mortality due to excessive temperatures today and the estimated number of temperature-related deaths in the mid-21st century.

The National Center for Health Statistics (NCHS) provided mortality data. The Gridded Meteorological Data Set (gridMET) provided daily mean ambient temperature, i.e., minimum and maximum mean temperature at a spatial resolution of 4.0 km. The MACAv2-METDATA data set provided estimated daily temperatures for the mid-21st century.

Scientists used average daily temperatures from 1979 to 2000 (historical) to determine monthly days of intense heat (above 97.5°F).^t percentile) and very frigid days (below 2.5)^t percentile) for the 3,108 contiguous counties in the United States from 2008 to 2019.

They used temperature projections from 20 global climate models (GCMs) and county-level population estimates to calculate heat-related mortality from 2036 to 2065. They analyzed data from November 2023 to July 2024.

The exposure studies included monthly frequencies of excessive heat days for the periods 2008 to 2019 and 2036 to 2065. The researchers evaluated the exposure studies under the following greenhouse gas (GHG) emissions scenarios: Shared Socioeconomic Pathway (SSP) 2-4.5 and SSP5-8.5.

While SSP 2-4.5 indicated socio-economic growth with lower emissions growth, SSP5-8.5 indicated higher emissions resulting from fossil fuel-based socio-economic development.

The primary outcome measure was the annual raise in the mean predicted number of deaths associated with severe temperatures. Secondary outcomes were excess deaths in specific subgroups and regions. Poisson regression models with fixed effects for year, month, and county assessed the association between extreme temperatures and monthly death rates.

Participants were divided into subgroups based on age, sex, race/ethnicity, U.S. census tract, and county metropolitan status (according to the 2013 National Center for Health Statistics (NCHS) urban–rural classification).

The team divided participants into older adults ≥65 years and younger adults aged 18 to 64 years. Sensitivity analyses used thresholds above the 99th percentile and below the first percentile for extreme temperatures and the highest daily heat index (including relative humidity) to define intense heat.

Results

From 1979 to 2000, the average daily temperature thresholds in U.S. counties were 27°C for excessive heat and −6.4°C for extreme frigid. From 2008 to 2019, the United States averaged 13 days of intense heat and 8.2 days of extreme frigid per year.

Over the period 2036–2065, the projected mean number of extreme heat days was 41 and 52 for the SSP2-4.5 and SSP5-8.5 settings, respectively. The estimated mean number of extreme frigid days in the two scenarios was 3.2 and 2.6, respectively.

Mortality data included 30,924,133 people, of whom 50% were male, 6.3% were Hispanic, 12% were non-Hispanic black, and 79% were non-Hispanic white. Between 2008 and 2019, 8,249 people died on days with extreme temperatures in the United States.

During this time, each additional day of intense heat in a month resulted in a 0.1% raise in mortality among the elderly and a 0.2% raise in mortality among teenage people.

The study predicts that excessive heat will cause 19,349 deaths (135% more than in 2008–2019) and 26,574 deaths (222% more than in 2008–2019) under the SSP2-4.5 and SSP5-8.5 scenarios, respectively.

Black (278%) and non-Hispanic Hispanic (538%) adults are estimated to be more likely to experience an raise in mortality from severe heat illnesses by the mid-21st century than non-Hispanic whites (71%).

Under the SSP2-4.5 scenario, researchers found a 90 percent reduction in severe heat mortality in U.S. urban areas and a 29 percent reduction in nonmetropolitan areas.

In sensitivity assessments, the number of deaths related to severe temperatures would raise from 4897 to 15,413 in the SSP2-4.5 scenario and 23,383 in the SSP5-8.5 scenario. Including lagged monthly values ​​of extreme temperature days and maximum daily heat index gave comparable results.

Application

Based on the study’s results, heat-related mortality in the United States will raise significantly between 2036 and 2065.

The burden of temperature-related mortality would disproportionately affect non-Hispanic blacks and Hispanics. The results underscore the need to reduce the negative impacts of extreme temperatures on public health.