Extreme Weather Toolkit: Extreme Heat

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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: April 2024