Climate Change Is Driving More Warm Summer Nights in U.S. Cities

Analysis of 243 to 247 major U.S. cities reveals that 95% have seen an increase in unusually warm summer nights since 1970, with an average increase of 24 nights per summer. Using the Climate Shift Index (CSI), the report finds that human-caused climate change now strongly influences an average of 27 warm summer nights per year, compared to just one in the 1970s. The most severe impacts are concentrated in Florida and Puerto Rico, where some cities experience over two months of climate-driven warm nights annually. These trends exacerbate heat stress, disrupt sleep, and increase energy demand for air conditioning, disproportionately affecting vulnerable populations and those in urban heat islands.

• The number of unusually warm summer nights (defined as minimum temperatures above the 1991-2020 normal) has increased in 95% of 243 analyzed major U.S. cities since 1970, adding an average of 24 such nights per summer.
• Regional data shows the highest increases in warmer-than-normal summer nights occurred in the Southeast, South, and Southwest, with average increases between 33 and 35 nights. The cities with the largest individual increases were Reno, NV (79 nights), Albany, GA (73 nights), and Sarasota, FL (73 nights).
• Human-caused climate change has a growing influence on nighttime temperatures in all 247 analyzed U.S. cities. The average number of summer nights strongly influenced by climate change (CSI level 2 or higher) has risen from one per summer in the 1970s to 27 per summer currently.
• The most severe climate-driven nighttime warming is concentrated in Puerto Rico and Florida, where cities experience more than two months of unusually warm summer nights annually. San Juan, Puerto Rico, reports the highest average at 80 nights.
• Increased nighttime warmth correlates with higher energy demand, with cooling degree days increasing in 97% of the analyzed major U.S. cities since 1970.

APA

Climate Central (2026). Climate Change Is Driving More Warm Summer Nights in U.S. Cities. https://www.climatecentral.org/climate-matters/warm-summer-nights-us-cities

Chicago

Climate Central. Climate Change Is Driving More Warm Summer Nights in U.S. Cities. 2026. https://www.climatecentral.org/climate-matters/warm-summer-nights-us-cities.

Wikipedia

{{cite report |author=Climate Central |title=Climate Change Is Driving More Warm Summer Nights in U.S. Cities |date=12 August 2026 |url=https://www.climatecentral.org/climate-matters/warm-summer-nights-us-cities |access-date=23 October 2026 |via=Climate Insights Directory}}

BibTeX

@techreport{climatecentral2026climate, author = {{Climate Central}}, title = {{Climate Change Is Driving More Warm Summer Nights in U.S. Cities}}, institution = {Climate Central}, year = {2026}, month = aug, url = {https://www.climatecentral.org/climate-matters/warm-summer-nights-us-cities}, urldate = {2026-10-23}, note = {Indexed by Climate Insights Directory} }