The Hottest Summer Days in the U.S. Have Barely Warmed in the Last 40 Years
September 18th, 2025 by Roy W. Spencer, Ph. D.
The total warming of the hottest 3 days in each summer month averaged across 400 mostly-airport weather stations is only 1.2 deg. F over 40 years.
I recently posted about the weather observations from Reagan National Airport that showed the warmest days of summer have experienced no statistically significant warming in the last 40 years, despite this being the period of maximum radiative forcing from increasing atmospheric CO2.
Of course, you would never know this based upon media reports… in fact, most people are probably under the impression that our hottest days are rapidly getting hotter.
One commenter on my post (correctly) pointed out that what I presented was just one weather station. Well, now I have processed ~400 mostly-airport (WBAN) weather stations and over 2,000 cooperative observer (COOP) stations across the U.S.
Here’s a plot of those station locations.
https://www.drroyspencer.com/2025/09/the-hottest-summer-days-in-the-u-s-have-barely-warmed-in-the-last-40-years/
