Chapman University research reveals tropical rainforest soils may fuel climate change as the Earth warms – Accelerating global warming

Orange, Calif. — Sept. 16, 2025 — A new study led by the U.S. Forest Service, with Chapman University as a key senior collaborator, published in Nature Communications, suggests the Earth’s own tropical soils may contribute to climate change as global warming continues, releasing vast amounts of carbon dioxide (CO₂) as they warm and potentially accelerating a dangerous feedback loop.

Tropical forests have long been viewed as critical allies in the fight against climate change, natural systems that absorb excess carbon and cool the planet. But this new research shows that warming itself is causing these forests’ soils to release enormous amounts of CO₂, essentially flipping the script.

This matters to everyone. If rainforests begin acting as carbon sources instead of sinks, it could accelerate global warming far faster than previously predicted, affecting everything from sea-level rise and extreme weather to food security and public health. Understanding these feedback loops is essential if we are to prepare for, and hopefully prevent, the worst impacts of a rapidly changing climate.

The international research team, including Chapman Assistant Professor of Biological Sciences Dr. Christine Sierra O’Connell, found that soil respiration in a Puerto Rican rainforest increased by 42–204% in experimentally warmed plots, one of the largest CO₂ release rates ever recorded in a terrestrial ecosystem. The findings position belowground ecosystems as critical players in the global climate crisis.

“This research shows that as the planet warms, tropical soils may begin to amplify that warming,” said O’Connell. “If these patterns persist across time and regions, we may be drastically underestimating the extent to which tropical forests will lose carbon and accelerate climate change.”

The study simulated a future climate scenario by raising atmospheric temperatures 4 °C using infrared heaters, marking the first such experiment in a tropical rainforest. Conducted through the TRACE (Tropical Responses to Altered Climate Experiment) project, which includes undergraduate researchers from Chapman University working alongside faculty in the field, the work suggests that microbes, not plant roots, were responsible for the dramatic CO₂ increases. These findings are significant because soils store more carbon than the atmosphere and all terrestrial plants combined. Releasing that carbon could amplify warming globally.

“We are witnessing a troubling shift,” O’Connell added. “The very systems we rely on to stabilize the climate may now be pushing us in the opposite direction.”

Researchers from the USDA Forest Service, US Geological Survey, University of Vermont, Morton Arboretum, and Michigan Technological University also contributed to the study.

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About Chapman University  
Founded in 1861, Chapman University is a nationally ranked private university in Orange, California, about 30 miles south of Los Angeles. Chapman serves nearly 10,000 undergraduate and graduate students, with a 12:1 student-to-faculty ratio. Students can choose from over 100 areas of study within 11 colleges for a personalized education. Chapman is categorized by the Carnegie Classification as an R2 “high research activity” institution. Students at Chapman learn directly from distinguished world-class faculty including Nobel Prize winners, MacArthur fellows, published authors and Academy Award winners. The campus has produced a Rhodes Scholar, been named a top producer of Fulbright Scholars, and hosts a chapter of Phi Beta Kappa, the nation’s oldest and most prestigious honor society. Chapman also includes the Harry and Diane Rinker Health Science Campus in Irvine. The university features the No. 4 film school and No. 66 business school in the U.S. Learn more about Chapman University: www.chapman.edu.

Media Contact:

Bob Hitchcock, Director of Strategic Communications | rhitchcock@chapman.edu | Mobile: 407-388-4657