Tropical cyclones have long pushed carbon out of the ocean and into the atmosphere, but new research shows that dynamic is rapidly changing — and the consequences for marine life and climate could be severe.
Tropical cyclones — the category that includes hurricanes and typhoons — have spent decades acting as a force that releases carbon from the ocean into the air. But a sweeping new study published in Nature Geoscience finds that global warming is quietly flipping that role, and if greenhouse gas emissions continue unchecked, cyclones could begin pulling carbon into the ocean by around 2035. That shift, counterintuitive as it sounds, would accelerate ocean acidification and shrink habitats for marine species.
What the Research Found
An international team of scientists built a first-of-its-kind daily dataset of global air-sea carbon dioxide flux, stitching together observations that have historically been too sparse to draw firm conclusions. The dataset allowed researchers to trace exactly how much carbon tropical cyclones have been moving — and in which direction — since 1993.
The findings are striking. During the mid-1990s, from 1993 to 1997, tropical cyclones were responsible for roughly 16% of the global annual carbon exchanged between the ocean and atmosphere. By 2016 to 2020, that figure had dropped to just 4.5%. Across the major ocean basins since 1993, cyclones account for an average of 9% to 23% of ocean carbon outgassing — but that share has fallen by more than half since the 2010s.
The mechanism behind the shift comes down to ocean stratification. As the planet warms, the sea surface heats up faster than deeper water below it. This steepens the vertical temperature gradient in the upper ocean. When a tropical cyclone passes and its powerful winds mix the surface with cooler water underneath, the resulting “cold wake” is now more pronounced than it was decades ago. That cooler surface water absorbs more carbon dioxide from the atmosphere — partially and increasingly more than offsetting the carbon the storm itself churns out.
Why It Matters for the Planet
The study was led by researchers at the National University of Defense Technology, Chinese Academy of Sciences, the NSF National Center for Atmospheric Research, and the GEOMAR Helmholtz Centre for Ocean Research Kiel. Co-author Zhanhong Ma, a professor in the College of Meteorology and Oceanography at the National University of Defense Technology, described why the findings are significant.
“The role of tropical cyclone in the global carbon cycle has long been obscure, owing to sparse observations during and after tropical cyclones. This work provides a sophisticated global air-sea carbon flux dataset, enabling exploration of the tropical cyclone contribution in the context of global warming,” Ma said in a news release.
The research team modeled two future scenarios: one in which human carbon emissions remain high, and one in which they are brought under control. Under the high-emissions path, cyclones are projected to cross the threshold from net carbon release to net carbon absorption around 2035. Under aggressive emissions reductions, that reversal would be delayed until roughly the 2040s — and it would take until the end of the century for ocean carbon uptake to return to current levels.
On the surface, more carbon absorbed by the ocean might sound like a climate win. It isn’t. The ocean already takes in an estimated 20% to 30% of all human-caused CO2 emissions each year — roughly 1 to 3 petagrams annually. When that absorption accelerates, seawater becomes more acidic. Acidification disrupts the chemistry marine organisms depend on to build shells and skeletons, threatening ecosystems from coral reefs to fisheries that billions of people rely on for food and livelihoods.
What This Means for Students and Young People
For college students studying environmental science, oceanography, atmospheric science, or policy, this research illustrates just how deeply interconnected Earth’s systems are. A phenomenon most people associate with hurricane season and coastal destruction turns out to be a meaningful variable in the global carbon budget — and its role is being rewritten in real time by warming the planet has already locked in.
The study also underscores a broader lesson about feedback loops: climate change does not simply intensify existing processes. It can reverse them entirely. The cold wakes that tropical cyclones leave behind can linger for weeks to over a month, quietly drawing down atmospheric carbon at a rate that grows more significant with each passing decade of warming.
For students interested in marine biology or conservation, the acidification angle is particularly urgent. As cyclones shift from carbon sources to carbon sinks, the chemical changes in seawater will accelerate habitat loss for marine species, adding pressure to ecosystems already stressed by warming temperatures and deoxygenation.
The Bottom Line
The science is clear: whether tropical cyclones remain a net carbon source or cross over into net carbon absorption depends almost entirely on the trajectory of human emissions. The authors stress that immediate action on carbon mitigation is the only lever available to delay — and potentially moderate — the reversal.
Source: Institute of Atmospheric Physics, Chinese Academy of Sciences