California summers are getting hotter. This map shows the most dramatic increases
But some places have warmed more than others. While greenhouse gas emissions have made temperatures rise around the planet, other drivers have influenced climate conditions too, on a more local scale. The Chronicle examined gridded temperature data trends to find where summers warmed the fastest in California from 1950 to 2024.
The map above is based on gridded temperature data from the National Oceanic and Atmospheric Administration. This data incorporates observations from climate stations — which can move over time — and computes temperatures across the contiguous United States. The Chronicle used the Climate Engine tool to calculate the trends shown.
Scientists are still working out how much urbanization, elevation and the ocean collectively impact warming. Other drivers have effects too, including long-term climate patterns like the Pacific Decadal Oscillation, which alters weather patterns in California.
Aerosol pollution also dramatically decreased over the U.S. in recent decades. While the cleanup is a boon for air quality, the drop in sunlight-blocking particles in the atmosphere results in more warming on the ground.
The variable nature of weather further complicates analyses, leading to ups and downs in average summer temperatures from year to year. July 2024 brought record-breaking heat across California; this month, the Bay Area generally faced cooler-than-average conditions. But over the course of decades, a rising trend emerges, especially in places like Fresno.
Summer heat can have deadly consequences. From 2013 to 2022, seven extreme heat events killed nearly 460 Californians, according to a Department of Insurance report. These events led to over 5,000 hospitalizations and more than 300 cases of adverse birth outcomes, including preterm births and stillbirths.
Some cities are taking steps to mitigate public health impacts of extreme heat. Fresno aims to cover 20% of the city with tree canopies over the next 40 years. This target requires planting around 4,600 trees per year. Fresno has planted about 7,600 trees since 2022, said Sontaya Rose, director of communications for the city, by email.
Even historically cool locations, like San Francisco, are preparing for hot summers. In 2023 and 2024, the city provided 62 air conditioning units to 23 community-based organizations through the Extreme Weather Resilience Program, according to the Department of Emergency Management. The equipment helps the organizations, including Self-Help for the Elderly and Boys & Girls Club of San Francisco, maintain services for vulnerable populations.
Scientists expect California temperatures to continue rising in the future, underscoring the importance of preparing communities for the impacts of extreme heat — especially where temperatures are rising the fastest.
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Reporting, design and development by Jack Lee. Editing by Hannah Hagemann, Dan Kopf and Aseem Shukla. Powered by the Hearst Newspapers DevHub.
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