Extreme Weather Toolkit: Extreme Heat

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

Global average temperatures have warmed by about 1.3C (2.3°F) relative to a 1850–1900 baseline. When global 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 mainly due to rising atmospheric concentrations of heat-trapping gases from burning fossil fuels (coal, oil, and gas), changing land use, and other human activities.

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

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

People living in urban areas also have a higher risk of extreme-heat exposure. 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 65 large U.S. cities analyzed by Climate Central, 34 million people live in neighborhoods made at least 8°F hotter because of characteristics of the built environment.  

In major U.S. cities, multi-day heat waves are longer, more intense, more frequent, and happening over a longer period of the year 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 21^st century. 

Every bit of additional warming brings greater heat-related risks for health, agriculture, and ecosystems. 

Updated: May 2025

Resources

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

Search our resource library

Climate Shift Index

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

Climate Matters

Urban Heat Hot Spots in 65 Cities

New Climate Central analysis shows where urban heat is most intense in 65 major cities that account for 15% of the U.S. population.

Climate Matters

2025 Summer Package

Summers are heating up in 234 of major U.S. cities — by an average of 2.6°F since 1970.

Climate Matters

Extreme Heat Risks for Children

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

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

Scorching Days Followed by Sweltering Nights

When hot summer days are followed by hot nights, the health risks grow. These combined hot summer day-night events are on the rise across the U.S. and around the globe.

Climate Matters

More Extremely Hot Days for School Sports

Young athletes heading back to practice this summer could face more extreme heat hazards.

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

Rising Heat Risks for Workers

Humid heat is especially dangerous for weather-exposed workers. It’s been rising as our climate warms.

Climate Matters

Risky Summer Heat Added by Climate Change

New analysis shows that carbon pollution drove risky heat across the globe and in the U.S. this summer.