Extreme Weather Toolkit: Extreme Heat

More frequent and intense extreme heat — the deadliest weather-related hazard in the U.S. — is a direct result of a warming planet.

Global surface temperature has increased by about 2°F relative to 1850–1900. When average temperatures warm, extreme heat events become more frequent. 

According to the latest IPCC reports, the frequency and intensity of extreme heat events has increased around the globe — and these changes are attributed to human-caused climate change.

Extreme heat is the deadliest weather-related hazard in the U.S. Children and adults over 65 are among those most vulnerable to heat-related illness and death. 

About 80% of the U.S. population lives in metropolitan areas, where urban heat islands can reach peak temperatures up to 20°F hotter than nearby areas with more trees and less pavement. 

Across 44 large U.S. cities analyzed by Climate Central, 41 million people live in census tracts with an urban heat island index of 8°F or higher. Characteristics of the built environment make these areas at least 8°F hotter.

In major U.S. cities, multi-day heat waves are now lasting longer and occurring three times more often than they did in the 1960s.

With continued heat-trapping emissions, both average temperatures and heat extremes are projected to continue to rise through the 21st century. 

In the absence of adaptation measures or reduced exposure of vulnerable people and systems, every bit of additional warming brings greater heat-related risks for health, agriculture, and ecosystems. 

Climate Central’s Climate Shift Index tool quantifies the influence of human-caused climate change on daily temperatures. 

Updated: June 2024

Resources

These resources explore the science, trends, and local impacts of extreme heat in the U.S.

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Climate Shift Index

Revealing the influence of climate change on local weather around the globe, every day.

Climate Matters

Urban Heat Hot Spots

New Climate Central analysis shows where urban heat is most intense in 44 major U.S. cities accounting for nearly one-quarter of the U.S. population.

Climate Matters

Hot Summer Days Linked to Climate Change in U.S. Cities

Summer 2023 was Earth’s record hottest. New analysis of 244 U.S. cities shows that the South, Southwest, and Southeast felt the strongest influence of climate change on summer heat.

Climate Matters

More Risky Heat Days in 232 U.S. Locations

The annual number of risky heat days has increased in 232 U.S. locations since 1970, according to Climate Central analysis.

Climate Matters

Sweltering Summer Nights

Sweltering summer nights are a serious health risk, and they’re heating up in 230 U.S. locations.

Climate Matters

Extreme Heat Risks for Children

Climate change is driving more frequent and intense extreme heat that is especially dangerous for children.

Report

Climate Change & Children's Health: Extreme Heat

Climate change is boosting temperatures and driving more frequent and intense extreme heat that is dangerous for children.

Climate Matters

More Extremely Hot Days

Extremely hot days have become more frequent in 195 U.S. cities since 1970—putting health at risk more often.

Climate Matters

High Heat Index Days

High heat index days—a serious health risk—have become more frequent in 201 U.S. locations.

Climate Matters

2023 Summer Package

THIS IS NOT THE MOST RECENT VERSION AVAILABLE. Summer is here and hotter than ever. Summers have warmed in 229 U.S. locations—by 2.4°F on average since 1970.

Climate Matters

Heat and Hospitalizations

As our climate continues to change, we are experiencing more extremely hot days, increasing the risk of heat-related illness and hospitalizations.

Climate Matters

Humid Heat: Hidden but Hazardous

When extreme heat is combined with high humidity, the health risks multiply. Summertime humid heat has increased three times more than air temperatures across the U.S. since 1950.