Warm Spring Days Boosted by Climate Change in U.S. Cities

Using the Climate Shift Index (CSI), Climate Central found that human-caused climate change significantly boosted spring warmth in 2024, affecting 300 million people in the U.S. and approximately one in four people globally. The strongest influence was observed in coastal and island regions, such as Puerto Rico and Florida, while areas with the highest temperature anomalies, like the Upper Midwest, showed lower CSI levels due to higher historical temperature variance.

• In the United States, approximately 300 million people, representing 89% of the population, experienced at least one spring day from March to May 2024 where warm average temperatures were made at least two times more likely by climate change (CSI level 2 or higher).
• The strongest influence of climate change in the U.S. was concentrated in coastal states and islands. San Juan, Puerto Rico, had the highest impact, with 91 days at CSI level 2 or higher, meaning 99% of all spring days were influenced. Other high-impact cities included Sarasota, Florida (39 days), West Palm Beach, Florida (35 days), Honolulu, Hawaii (32 days), and Miami, Florida (31 days).
• There is a distinction between temperature anomalies and the CSI signal. States with the highest temperature anomalies, such as Michigan (4.0°F), Ohio (3.9°F), and West Virginia (3.7°F), had fewer than four spring days at CSI level 2 or higher because these regions have higher seasonal temperature variance and more modest long-term warming trends.
• Globally, about 25% of the population experienced a very strong influence of climate change (CSI level 3 or higher) on temperatures daily from March to May 2024. This peaked on April 6, 2024, affecting 2.7 billion people. The most extreme attributable heat (CSI level 5 for at least 60 days) affected approximately 44% of people in Africa and one in three people in South America.
• Climate-driven spring warming has several ecological and societal impacts: it lengthens the freeze-free growing season (observed in 164 of 197 analyzed U.S. cities since 1970), extends the season for disease-carrying pests like mosquitoes, shifts plant hardiness zones northward, and causes earlier snowmelt that reduces water supplies for hydropower, agriculture, and drinking water.

APA

Pershing, A. (2024). Warm Spring Days Boosted by Climate Change in U.S. Cities. Climate Central. https://www.climatecentral.org/climate-matters/2024-us-spring-attribution

Chicago

Pershing, Andrew. Warm Spring Days Boosted by Climate Change in U.S. Cities. Climate Central, 2024. https://www.climatecentral.org/climate-matters/2024-us-spring-attribution.

Wikipedia

{{cite report |last1=Pershing |first1=Andrew |title=Warm Spring Days Boosted by Climate Change in U.S. Cities |publisher=Climate Central |date=5 June 2024 |url=https://www.climatecentral.org/climate-matters/2024-us-spring-attribution |access-date=23 October 2026 |via=Climate Insights Directory}}

BibTeX

@techreport{pershing2024warm, author = {Pershing, Andrew}, title = {{Warm Spring Days Boosted by Climate Change in U.S. Cities}}, institution = {Climate Central}, year = {2024}, month = jun, url = {https://www.climatecentral.org/climate-matters/2024-us-spring-attribution}, urldate = {2026-10-23}, note = {Indexed by Climate Insights Directory} }