Ship emissions found to warm the planet more than expected
image: Global distribution and warming effect of brown carbon from shipping emissions
Credit: Yiyang Sun, Junjun Deng, Fan Zhang, Wei Hu, Yan Zhang, Yingjun Chen, Yunting Xiao, Lehui Cui, Yaxin Liu, Jiaming Zhao & Jialei Zhu
A new study led by researchers at Tianjin University reveals that particles from shipping exhausts are contributing more to global warming than previously thought. The study identifies “brown carbon,” a light‑absorbing component of ship emissions, as a hidden driver of heat retention in the atmosphere.
Shipping keeps the global economy moving, with vessels burning millions of tons of fuel each year. While scientists have long known that ships release black carbon and sulfur aerosols, which affect the Earth’s radiation balance, organic carbon from shipping was usually considered harmless. This new research overturns that assumption by showing that brown carbon particles from ship fuel can absorb sunlight and exert a warming influence, especially over ocean surfaces.
Using a global climate model combined with observational measurements from marine engines, the researchers calculated the radiative absorption effect of brown carbon. They found that brown carbon makes up roughly 60 percent of all ship‑related carbon particles. Its heating effect ranges from 0.15 to 0.36 milliwatts per square meter globally, accounting for up to one‑fifth of the warming impact caused by black carbon from ships.
The effect is especially strong along major shipping routes such as the Mediterranean, North Atlantic and western Pacific, where concentrations of brown carbon reach their highest levels. Seasonal patterns were also observed, with the strongest warming effect occurring during the Northern Hemisphere’s summer when trade and transport activity peak.
The study further examined how the International Maritime Organization’s low‑sulfur fuel standards, implemented in 2020, have changed this balance. While these cleaner fuels significantly cut sulfur emissions and reduce the cooling effects linked to sulfate particles, they also increase the organic carbon fraction in exhaust gases. As a result, brown carbon now absorbs nearly as much solar energy as black carbon, potentially offsetting up to 40 percent of the cooling previously provided by shipping sulfate aerosols.
Lead author Yiyang Sun explained that these findings fill a major gap in climate modeling. “Our work shows that as sulfur emissions fall, the warming contribution from brown carbon becomes increasingly important. Understanding this shift is crucial for developing policies that truly mitigate shipping’s climate impact.”
The researchers call for more high‑resolution measurements of marine aerosol composition and improved global emission inventories to better quantify shipping’s role in future climate change.
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Journal Reference: Sun, Y., Deng, J., Zhang, F. et al. Global distribution and warming effect of brown carbon from shipping emissions. Carbon Res. 4, 44 (2025). https://doi.org/10.1007/s44246-025-00212-w
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