Every year, around 90 tropical cyclones form in our oceans. Scientists long thought these storms released carbon dioxide (CO2) from the sea into the atmosphere. However, measuring this accurately has been tricky. Ships avoid hurricanes, and sensors often fail in storms. As a result, estimates of CO2 release varied widely, leaving researchers puzzled.
A recent study published in Nature Geoscience finally sheds light on this issue. Researchers from China, the U.S., and Germany created a global dataset from 1993 to now, detailing air-sea carbon flux during cyclones. Instead of sending tools into storms, they analyzed satellite data and reconstructed chemical changes in the ocean during and after each cyclone. This has created a comprehensive view of carbon movement during these intense weather events for the first time.
What they found is surprising. While cyclones initially push CO2 into the air, they also mix cold water from the ocean’s depths, which absorbs CO2 after the storm passes. This cooling effect can last for weeks, partially offsetting the initial outgassing.
Historically, in the early 1990s, cyclones contributed about 16% of carbon flux in tropical regions. By the late 2010s, this dropped to around 4.5%. The reduction was almost a halving of total carbon released due to cyclones.
Zhanhong Ma, a researcher involved in the study, explains, “This work provides a sophisticated global air-sea carbon flux dataset, allowing for exploration of tropical cyclone contributions amid global warming.” The findings highlight how warming oceans are changing this dynamic.
As surface temperatures rise faster than deeper ocean layers, cyclones mix even colder water to the surface, enhancing the ocean’s ability to absorb CO2 during recovery. Consequently, storms today may pull back more carbon than they did thirty years ago.
In specific regions like the Bay of Bengal, cyclones have historically released a significant amount of CO2. Many rely on cyclones, which can account for half of local annual CO2 emissions.
The future is uncertain. Under a high-emissions scenario, cyclones may shift from being carbon sources to sinks around 2035. While this might sound promising, it’s not entirely good news. An ocean that absorbs more CO2 becomes more acidic, affecting marine life that relies on calcium carbonate, like corals and shellfish.
Different modeling approaches show varied predictions for cyclone activity in the future. While the cold wake mechanism is clear, the interactions between ocean biology, chemistry, and circulation can still be ambiguous. Nevertheless, the broad trends are evident: cyclones are not just extreme weather but also play a complex role in our climate system.
This research reveals that hurricanes are not just threats to communities but also influence global carbon levels. As our climate changes, the impact of these storms on the carbon cycle must be closely monitored.
For more details on this study, visit Nature Geoscience.
