Tropical cyclones churn the ocean surface with devastating winds, but scientists have now discovered something more subtle happening beneath the spray: they're reshaping how the sea absorbs and releases carbon. An international research team has found that these extreme storms currently push net carbon out of the ocean and into the atmosphere—but global warming could flip that entirely by 2035, with consequences far more troubling than the storms themselves.
The ocean already does heavy lifting for humanity, absorbing 20–30% of anthropogenic carbon emissions each year. Understanding how tropical cyclones fit into this equation matters enormously, yet their role has remained unclear until now. Led by researchers from China's National University of Defense Technology and institutions including the NSF National Center for Atmospheric Research and Germany's GEOMAR Helmholtz Centre, a new study published in Nature Geoscience synthesized decades of observations into a daily global air-sea CO2 flux dataset—overcoming the challenge of sparse measurements during and after storms.
The findings are striking. Between 1993 and 1997, tropical cyclones contributed roughly 16% of the global annual ocean carbon flux, acting as carbon sources that released the gas to the atmosphere. The strong winds over storm surge areas dramatically enhanced CO2 transfer from sea to air. Yet by 2016–2020, this fraction had plummeted to just 4.5%—a drop driven by an unexpected mechanism. As the ocean warms unevenly, the temperature difference between the surface and deeper waters sharpens. When tropical cyclones pass, they leave behind colder patches called "cold wakes" that now persist for weeks or longer. These cooler zones actually pull more carbon from the atmosphere into the sea, partly offsetting the carbon released by the initial wind-driven outgassing.
But the silver lining darkens further. If humanity maintains high levels of carbon dioxide emissions, the trend will reverse entirely around 2035. Tropical cyclones would shift from being carbon sources to carbon sinks—and that's actually the worse outcome. As the storms enhance ocean carbon uptake, they would accelerate ocean acidification, a chemical transformation that shrinks habitats and threatens marine life survival. The research team emphasizes that this scenario hinges on human choice: emission decisions made in the next decade will determine whether tropical cyclones remain carbon sources, stabilize, or become carbon sinks.
There is a narrowing window for prevention. If emissions are controlled immediately, the downward trend in cyclone-driven carbon outgassing would likely not reverse until the 2040s, and it would take until century's end for carbon uptake to return to current levels. The research reveals that tropical cyclones have contributed between 9% and 23% of ocean carbon outgassing in major basins since 1993, a contribution that has already halved within recent decades—not because storms weakened, but because the warming ocean itself changed how they interact with atmospheric gases.
"This work provides a sophisticated global air-sea carbon flux dataset, enabling exploration of the tropical cyclone contribution in the context of global warming," said Prof. Zhanhong Ma, a co-author from the National University of Defense Technology. The discovery clarifies a critical blind spot in climate science, showing that extreme weather and long-term warming are locked in a dangerous dance. The question now is whether humanity will step back from that dance before 2035.