Climate Change Driving 55-Year Rise in Extremely Hot Summer Days

An attribution analysis reveals that 88% of 247 major U.S. cities have seen an increase in extremely hot summer days strongly influenced by climate change since 1970. On average, these cities now experience six such days annually, compared to zero in the 1970s, with the most significant increases occurring in the South, particularly in Texas and Louisiana.

• Since 1970, 88% (217) of the 247 analyzed major U.S. cities have experienced an increase in the frequency of extremely hot summer days that show a strong climate change signal.
• The average number of extremely hot summer days with a strong climate change fingerprint (CSI level 2 or higher) in these 217 cities has risen from zero in the 1970s to approximately six days per year between 2000 and 2024.
• The South and Southwest are disproportionately affected; more than half of the 74 cities experiencing at least seven additional extremely hot summer days per year (2020-2024) compared to the 1970s are in these regions. Specifically, seven of the top 10 cities with the largest increases are in Texas (Abilene, Waco, San Angelo, Austin, and Odessa) and Louisiana (Lafayette).
• Extreme heat is the primary cause of weather-related deaths in the U.S., with a record 2,325 deaths reported in 2023, though this is considered an undercount.
• Vulnerable populations and marginalized communities face higher risks; children, adults over 65, and pregnant people are most at risk, while people of color and those below the poverty line are disproportionately exposed to intense heat in urban heat islands in 169 of the largest U.S. cities.

APA

Climate Central (2025). Climate Change Driving 55-Year Rise in Extremely Hot Summer Days. https://www.climatecentral.org/climate-matters/extremely-hot-summer-days-2025

Chicago

Climate Central. Climate Change Driving 55-Year Rise in Extremely Hot Summer Days. 2025. https://www.climatecentral.org/climate-matters/extremely-hot-summer-days-2025.

Wikipedia

{{cite report |author=Climate Central |title=Climate Change Driving 55-Year Rise in Extremely Hot Summer Days |date=4 June 2025 |url=https://www.climatecentral.org/climate-matters/extremely-hot-summer-days-2025 |access-date=23 October 2026 |via=Climate Insights Directory}}

BibTeX

@techreport{climatecentral2025climate, author = {{Climate Central}}, title = {{Climate Change Driving 55-Year Rise in Extremely Hot Summer Days}}, institution = {Climate Central}, year = {2025}, month = jun, url = {https://www.climatecentral.org/climate-matters/extremely-hot-summer-days-2025}, urldate = {2026-10-23}, note = {Indexed by Climate Insights Directory} }