New research published in Nature Climate Change estimates that vessels operating on rivers and canals generated about 24.7% of global shipping CO₂ emissions in 2022, despite inland waterways accounting for less than 1% of the world’s navigable waterways.
Researchers in China analyzed around 20 billion vessel-tracking records collected between 2019 and 2022 to estimate emissions from inland shipping. The data identified 12,289 rivers and canals with sustained vessel activity.
The researchers noted that conventional vessel-tracking data can contain significant gaps, while standard route reconstruction methods may incorrectly show ships crossing land when navigating winding rivers. To address these limitations, the team developed a route reconstruction model that more accurately mapped vessel movements along river networks.
The reconstructed vessel routes were then combined with information on ship characteristics to estimate fuel consumption and exhaust emissions.
The analysis found that inland vessels emitted about 164 million metric tonnes of CO₂ in 2022, equivalent to 149 million tonnes and 24.7% of total global shipping emissions. Emissions from river and canal shipping almost doubled between 2019 and 2022, with the increase driven mainly by growing vessel activity and economic demand, particularly in Asia.
Emissions were heavily concentrated in a relatively small number of waterways. About 69% of the total came from just 20 major rivers, including the Yangtze, Rhine, Mississippi and Danube.
Cargo vessels were the largest source of inland shipping emissions, accounting for roughly two-thirds of the sector’s CO₂ output.
The researchers also compared shipping emissions with natural CO₂ releases from the same rivers. Inland vessel emissions were estimated to be around 80% of the amount of CO₂ naturally released by the navigable waterways through processes including the breakdown of organic matter and soil runoff.
Emissions also varied depending on the season and local hydrological and climatic conditions. According to the researchers, both economic demand and the physical capacity of waterways to support navigation influence the amount of pollution generated by inland vessels.
The findings highlight the distinctive role of navigable rivers in the global carbon cycle, where natural carbon exchange and emissions from human activity occur within the same waterways at comparable scales.
The researchers described navigable rivers as “hybrid carbon environments”, in which natural river-atmosphere CO₂ exchange coexists with emissions from commercial vessel traffic.
