The elevated geopolitical tensions around the Strait of Hormuz are a reminder of the central importance of maritime shipping for the global economy. Maritime transport is the backbone of global trade: roughly 80 percent of the goods we consume worldwide are carried by sea. Yet this vital network comes with significant environmental costs. Shipping is a major and growing source of global greenhouse gas emissions, contributing to climate change. At the same time, the combustion of fossil fuels in vessel engines releases harmful air pollutants, including nitrogen oxides (NOₓ), sulfur oxides (SOₓ), and fine particulate matter (such as PM2.5 and PM₁₀), that pose serious risks to human health, particularly for communities near ports and along busy shipping routes, as previous research as shown1,2.
Over the past several years, our team has developed the most comprehensive and high-resolution maritime vessel emissions dataset available (to our knowledge) through a partnership with Global Fishing Watch (GFW), OceanMind, and Climate TRACE. This first-of-its-kind dataset quantifies emissions from all industrial ocean-going vessels, leveraging Automatic Identification System (AIS) to estimate vessel-level emissions for all broadcasting vessels in near-real time.
To demonstrate how the data can be used in practice, we zoom in to the San Pedro Bay port complex, the busiest port complex in the United States and one of the busiest in the world. This port complex comprises the Port of Long Beach and the neighboring Port of Los Angeles. Figure 1 reveals the immense scale and concentration of emissions associated with shipping activities in the Port of Long Beach. In 2025 alone, more than 34,000 vessel trips to and from the port were associated with roughly 5.5 million metric tons of attributed CO₂ emissions. This represents nearly 25% of the total 16.3 million metric tons emitted by the Port of Los Angeles that year—and accounts for 0.5% of all global CO₂ emissions from AIS-broadcasting marine vessels in 20253. A striking result is that international shipping accounts for a disproportionate share of this footprint: although only about 11 percent of trips were international, they generated more than 90 percent of attributed trip emissions. Trade with Asia plays an especially important role, with routes connected to China and South Korea accounting for more than half of emissions from international trips.
Figure 1: Spatial distribution of CO2 emissions that occurred during trips that ended at or departed from the Port of Long Beach, aggregated across all trips that finished in 2025. Emissions are shown for 0.1x0.1 degree pixels and are normalized by pixel area. An inset is shown for the area of southern California around the Port of Long Beach.
The analysis also shows how emissions are highly concentrated across vessel types, with container ships responsible for roughly two-thirds of all attributed trip emissions, despite representing less than 10 percent of trips. Importantly, these same activities generate substantial co-emissions of local air pollutants, including nitrogen oxides (NOₓ), sulfur oxides (SOₓ), and fine particulate matter (PM2.5), linking global trade flows directly to local air quality and health impacts.
The data also highlight that shipping’s environmental impacts are not limited to emissions generated at sea, but also include substantial emissions from vessels maneuvering within ports and while docked at port. Ships operating at berth and maneuvering within the port generated nearly one million metric tons of CO₂ in 2025 (roughly 20% of total emissions), while also producing substantial emissions of NOₓ, SOₓ, and PM2.5 that affect air quality in and around the port (Figure 2). The emissions from ships just sitting at the dock are equivalent to adding a permanent, 24/7 traffic jam of a quarter-million cars to the streets of Long Beach4. These emissions matter because they occur close to communities already burdened by freight-related pollution, making ports a critical nexus of both climate and environmental inequality concerns.
Figure 2: Monthly emissions of NOX, SOX, and PM2.5 that occurred during port stays in the Port of Long Beach from January 2021 through March 2026.
These results show how high-resolution vessel-level data can identify where both greenhouse gases and harmful co-pollutants are generated, and where interventions such as cleaner fuels, improved vessel technologies, shore power, and port electrification could deliver substantial climate and public health benefits. By strengthening the evidence-base through granular, actionable data, we hope to identify the innovative policy levers required to move from evaluation to impact.
Footnotes:
- https://iopscience.iop.org/article/10.1088/1748-9326/ac146b
- https://www.nature.com/articles/s41467-017-02774-9
- https://climatetrace.org/explore#admin=Los%20Angeles%20Urban%20Area--%20USA:1709:ghs-fua_1642:city&gas=co2e&year=2025&timeframe=100§or=&asset=3167631
- https://www.epa.gov/energy/greenhouse-gas-equivalencies-calculator#results
