Global maritime CO₂ emissions climbed 9.3% between 2019 and 2024, increasing from 889.5 to 972.8 million metric tons, according to new analysis from the OECD. The report finds that while ships are becoming more fuel-efficient, rising economic activity, longer trade routes, and structural fleet trends continue to offset these gains. Shipping represented roughly 2.5% of global energy-related CO₂ emissions in 2024—placing it on par with some G7 economies.
Container ships and bulk carriers account for nearly half of global maritime CO₂ emissions. Over the five-year period, container ship emissions rose 14.7% while bulk carrier emissions increased 10.6%. The OECD attributes the spike largely to increased global trade volumes and higher transport intensity—tonne-miles growing faster than GDP.
Fleet characteristics also play a role. Vessels aged 20 years and older now number nearly 80,000 globally, up from about 70,000 in 2019, extending reliance on older, fossil-fueled hulls. Meanwhile, mega-containerships over 10,000 TEU now represent about 42% of the world’s container capacity. While these larger vessels offer better per-tonne fuel performance, they also lock in long-lived fossil infrastructure.
The analysis uses a decomposition method to identify major forces influencing emissions. Fuel intensity—the fuel required per unit of nominal capacity—showed the strongest downward effect, indicating that ships are operating more efficiently due to slow steaming, operational improvements, and compliance with IMO’s Energy Efficiency Existing Ship Index (EEXI) and Carbon Intensity Indicator (CII). These regulatory shifts, however, have not significantly altered the sector’s fuel mix, which remains dominated by oil-based fuels despite growth in LNG and early adoption of methanol-ready designs.
Distance-driven emissions turned positive in the latter part of the period. Geopolitical disruptions—including Red Sea rerouting, Panama Canal constraints from drought, and altered trade flows following Russia’s invasion of Ukraine—pushed vessels onto longer routes. This added millions of tonne-miles to global shipping activity and reduced the emissions benefits gained through efficiency.
Capacity utilization trends vary by region. Globally, underutilization has increased emissions by leaving more tonnage in operation than needed. In the OECD fleet, utilization improved slightly, exerting a modest downward effect.
The OECD’s findings underscore the scale of the challenge facing the maritime sector as it works toward the IMO’s 2050 net-zero ambition and interim 2030 and 2040 reduction targets. Efficiency gains alone continue to be overtaken by market-driven factors—particularly the growth of global trade and rerouted maritime corridors.
Regulations entering force after 2024 will exert stronger pressure. The EU Emissions Trading System now applies to large ships entering European ports, and FuelEU Maritime will begin limiting the lifecycle carbon intensity of fuels. These measures are expected to push operators toward low-carbon fuels such as green methanol, ammonia, or advanced biofuels—pathways that E+E Leader reporting has shown carry both potential and sustainability risks.
For companies with maritime-linked supply chains, the report highlights rising exposure to carbon costs and route volatility. Many firms are already reevaluating procurement strategies, assessing the carbon intensity of shipping partners, and tracking whether carriers invest in alternative-fuel vessels.
The OECD’s analysis ultimately reinforces a key trend across the global transport sector: operational efficiency is improving, but structural patterns in trade, fleet composition, and fuel availability are determining emissions outcomes. Without accelerated investment in low-carbon fuels and technologies, maritime emissions are likely to remain on an upward trajectory despite regulatory tightening.
