Maritime emissions fell by 4.5% year-over-year in the second quarter of 2025, despite an 8% increase in the global fleet size.

In a report released on July 31, emissions tracking firm Vesselbot analyzed data from more than 72,000 voyages made by nearly 4,900 vessels between April and June 2025. Although Q2 emissions were down compared to that same quarter in 2024, total emissions in the first six months of 2025 actually increased by nearly a full percent, thanks in large part to a 16% jump in January, when the number of total trips rose by more than 13%, during a surge in cargo driven by businesses looking to get ahead of planned tariffs from the Trump administration. 

Vesselbot found that voyage duration spiked in the first half of 2025 as well — both in terms of time at sea and time spent at port — with twenty-foot-equivalent unit (TEU) kilometers for trips destined for Gibraltar, Rotterdam, Antwerp and Cape Town increasing by more than 20% in both January and May. That's blamed on a host of factors, including persistent congestion at European ports, as well as the ongoing conflict in the Red Sea that's been pushing carriers to reroute ships around Africa's Cape of Good Hope. 

While smaller vessels tend to emit less carbon per voyage on average, they also make more far trips than their larger counterparts. Because of that, smaller feeders accounted for more than a quarter of total container ship emissions in Q2 across nearly 45,000 voyages, the most of any vessel category in terms of both emissions share and total trips. Comparatively, Panamax vessels produced roughly 22% of emissions for the quarter across 13,204 voyages, while VLCS container ships accounted for 8.4% of emissions across 1,371 trips.