Extreme temperature deaths expected to surge in US by 2065 due to rising emissions

By Pooja Toshniwal PahariaReviewed by Lily Ramsey, LLMSep 24 2024

A new study highlights the rising threat of heat-related mortality in the US, projecting significant increases in deaths by mid-century, with minority populations and older adults facing the greatest risks due to climate change and rising greenhouse gas emissions.

Study: Projections of Extreme Temperature–Related Deaths in the US. Image Credit: Miguel AF/Shutterstock.com

In a recent study published in JAMA Network Open, researchers examined the current burden of severe temperature-related mortality in the contiguous United States (US), spanning 2008 to 2019. They also projected the temperature-related death load in the middle of the twenty-first century, i.e., between 2036 and 2065.

In the United States (US), extreme heat has increased significantly due to anthropogenic greenhouse gas emissions, whereas extreme cold has declined. Understanding the impact of severe temperatures and demographic changes on public health is critical for establishing strategies to prevent the health consequences of climate change.

Identifying subgroups based on age, gender, race, ethnicity, or residence may allow for more focused treatments to reduce adverse health consequences.

About the study

In the present cross-sectional study, researchers assessed mortality from excessively high temperatures in current times and estimated temperature-related fatalities during the middle of the 21st century.

The National Center for Health Statistics (NCHS) provided mortality data. The gridded surface meteorological (gridMET) dataset provided the daily average ambient temperature, i.e., the minimum and maximum temperature mean at a 4.0-km spatial resolution. The MACAv2-METDATA dataset provided the estimated daily temperatures in the middle 21st century.

The researchers used 1979-2000 (historical) daily average temperatures to derive monthly intense heat days (above 97.5^th percentile) and intense cold days (below 2.5^th percentile) for 3,108 contiguous United States counties between 2008 and 2019.

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

The study exposures included the monthly frequencies of excess heat days in the 2008-2019 and 2036-2065 periods. Researchers evaluated the study exposure based on the following scenarios of greenhouse gas (GHG) emissions: Shared Socioeconomic Pathway (SSP) 2-4.5 and SSP5-8.5.

While SSP 2-4.5 denoted socioeconomic growth with a lesser rise in emissions, SSP5-8.5 indicated higher emissions from fossil fuel-based socioeconomic development.

The primary outcome measure was the annual increase in the average anticipated number of severe temperature-related fatalities. Secondary outcomes were additional deaths in specific subgroups and regions. Poisson regression models with fixed effects for variables like year, month, and county evaluated the relationship between extreme temperatures and monthly death rates.

Individuals were divided into subgroups based on age, gender, race, ethnicity, US Census area, and county metropolitan status (according to the 2013 National Center for Health Statistics (NCHS) Urban-Rural classification).

The team grouped the participants as older individuals ≥65 years old and younger ones aged 18 to 64 years. The sensitivity analyses used thresholds above the 99th percentile and below the first percentile for severe temperatures and the highest daily heat index (including relative humidity) to define intense heat.

Results

From 1979 to 2000, daily mean temperature thresholds in US counties were 27°C for excessive heat and −6.4°C for extreme cold. From 2008 to 2019, the United States saw an average of 13 days of intense heat and 8.2 days of extreme cold annually.

For the 2036-2065 era, the anticipated mean counts of extreme heat days were 41 and 52 for SSP2-4.5 and SSP5-8.5 settings, respectively. The estimated average extreme cold days in the two scenarios were 3.2 and 2.6, respectively.

The mortality information comprised 30,924,133 individuals, of whom 50% were male, 6.3% were Hispanic, 12% were non-Hispanic Blacks, and 79% were non-Hispanic Whites—between 2008 and 2019, severe temperature days caused 8,249 deaths in the United States.

During this time, one more intense heat day per month led to a 0.1% higher monthly death rate among older individuals and a 0.2% higher rate among young adults.

The study anticipated that excessive heat would cause 19,349 fatalities (135% more than the 2008-2019 era) and 26,574 deaths (222% more than the 2008-2019 period) under the SSP2-4.5 and SSP5-8.5 scenarios, respectively.

According to the estimates, adults of non-Hispanic Black (278%) and Hispanic origins (538%) will have higher increases in severe temperature-related mortality from now until the middle of the twenty-first century than non-Hispanic Whites (71%).

In the SSP2-4.5 scenario, the researchers noticed a 90% reduction in severe temperature-related mortality in US urban areas and a 29% reduction in non-metropolitan counties.

In the sensitivity assessments, severe temperature-related fatalities would rise from 4,897 to 15,413 in the SSP2-4.5 scenario and 23,383 in the SSP5-8.5 scenario. Including delayed monthly values of extreme temperature days and the maximum daily heat index produced comparable findings.

Conclusion

Based on the study findings, severe temperature-related mortality in the United States would considerably increase between 2036 and 2065.

The temperature-related mortality burden would disproportionately affect non-Hispanic Blacks and Hispanic individuals. The findings highlight the need to reduce the adverse effects of severe temperatures on public health.