Monthly Attribution Overview – December 2025

The report finds that while December 2025 temperatures in the U.S. were evenly split between warmer-than-average and cooler-than-average cities, long-term trends show nearly all analyzed cities have warmed since 1970. The Southwest was the most unusually hot region, with Casper, Wyoming, recording the highest anomaly. Climate signal (CSI) was minimal nationwide, though San Juan, Puerto Rico, saw 10 days where temperatures were at least five times more likely due to climate change.

• In December 2025, the average temperature anomaly across 194 analyzed U.S. cities was 0.4°F, with an even split of 95 cities being warmer than average and 95 being cooler than average. Twelve cities recorded their hottest December on record.
• Regional temperature variations were significant: the Southwest was the most unusually hot region with average anomalies exceeding 9.4°F, while the Southeast, Ohio Valley, Upper Midwest, and Northeast experienced cooler-than-average temperatures. Casper, Wyoming, was the most unusually warm city, 12.1°F above usual.
• Long-term data indicates that 191 out of 194 analyzed cities have shown warming trends for December since 1970. Wheeling, West Virginia, has seen the most significant December warming in this period, with its average December now 10.7°F warmer than in 1970.
• The Climate Signal Index (CSI) was minimal across most of the U.S. in December, with only four cities experiencing at least one week of days at or above CSI 2. However, San Juan, Puerto Rico, had 10 days at CSI 5, meaning temperatures on those days were at least five times more likely because of climate change.

APA

Climate Central (2026). Monthly Attribution Overview – December 2025. https://www.climatecentral.org/report/monthly-attribution-overview-december-2025

Chicago

Climate Central. Monthly Attribution Overview – December 2025. 2026. https://www.climatecentral.org/report/monthly-attribution-overview-december-2025.

Wikipedia

{{cite report |author=Climate Central |title=Monthly Attribution Overview – December 2025 |date=6 January 2026 |url=https://www.climatecentral.org/report/monthly-attribution-overview-december-2025 |access-date=23 October 2026 |via=Climate Insights Directory}}

BibTeX

@techreport{climatecentral2026monthly, author = {{Climate Central}}, title = {{Monthly Attribution Overview – December 2025}}, institution = {Climate Central}, year = {2026}, month = jan, url = {https://www.climatecentral.org/report/monthly-attribution-overview-december-2025}, urldate = {2026-10-23}, note = {Indexed by Climate Insights Directory} }