Blue Whales Blue Skies Emissions Analysis

GHG Emissions and Local Pollutants Impact of the 2024 BWBS Season

Introduction

Executive Summary

Motivation:

The Protecting Blue Whales and Blue Skies (BWBS) Vessel Speed Reduction (VSR) Program is a voluntary program whereby ship operators reduce their speed through certain speed reduction zones with the goal of reducing whale strikes, underwater noise, local pollution, and greenhouse gas (GHG) emissions. Existing research has already quantified the program’s local impact on the emissions that occur within the speed reduction zones themselves. However, there are questions as to whether vessels may be adjusting their behavior outside of the speed reduction zones as well (i.e., speeding up before and/or after they need to slow down), which could reduce or even reverse the net global greenhouse gas emissions benefits of the program.

Methods summary:

This report provides the first comprehensive assessment of the net global emissions impact of the 2024 BWBS season. Using AIS-based emissions estimates covering 3 GHGs and 6 local pollutants, we compare observed within-season emissions to a counterfactual constructed from each vessel’s pre-season (baseline) emission intensities applied to the distances traveled during the VSR season. By subtracting the counterfactual emissions estimates from the observed emissions estimates, we can estimate the impact of the program. We analyze program impact at three spatial scales: 1) global (both inside and outside VSR zones); 2) inside VSR zones; and 3) outside VSR zones.

Key findings:

• Of the 757 vessels listed as program participants from BWBS, we were able to match 738 to vessels in the Global Fishing Watch emissions database. Of these, only 321 had the necessary data to assess program impact (activity data from both inside and outside the VSR zones, and also from both before and during the VSR season). Of these, 243 vessels could be considered ‘compliant’: that is, they both: 1) had an average speed less than 10.4 knots inside the VSR zones during the VSR season; and 2) reduced their speed within VSR zones during the VSR season, compared to their speed within VSR zones outside the season. The results of our analysis focus on just these ‘compliant’ vessels in order to isolate the impact the BWBS program has on just those vessels abiding with program rules.
• Inside VSR zones, compliant vessels achieved a 25.5% reduction in CO₂e emissions relative to the counterfactual, demonstrating clear local emissions benefits.
• Inside VSR zones, most local pollutants also declined relative to the counterfactual NO_X by 13.4%, SO_X by 25.8%, and PM_2.5 by 4.5%. However, CH₄, CO, and VOCs increased relative to the counterfactual due engine combustion inefficiencies that occur at lower speeds.
• Outside VSR zones, CO₂e emissions increased by 1.3% relative to the counterfactual. This increase was driven by a subset of vessels (136 vessels, 56% of the compliant fleet) that sped up outside VSR zones. This may indicate ‘catch-up’ behavior to compensate for slower transit within the VSRs.
• The net global CO₂e emissions impact for compliant vessels is a 0.6% change relative to the counterfactual. This indicates that at a global scale, spillover effects outside the VSRs offset the local benefits inside the VSRs. This may be an example of ‘carbon leakage’.
• When isolating the 107 vessels that didn’t speed up outside the VSR zones (44% of the compliant fleet), a net global CO₂e emissions reduction of 5.9% is estimated. This highlights the program’s potential for global GHG benefits when vessels do not compensate outside VSR zones.
• Company-level heterogeneity reveals that some operators engage more deeply with the voluntary speed reductions, driving meaningful global reductions, while others do not.

These results provide a first comprehensive assessment of the BWBS program’s global emissions footprint and point to the importance of addressing catch-up behavior to maximize the program’s climate benefits.

About emLab and Partners

Environmental Markets Lab (emLab) at UC Santa Barbara (UCSB), in collaboration with Global Fishing Watch and Climate TRACE, have developed a first-of-its-kind near-real-time emissions database for all industrial vessels operating in the ocean. Our dataset covers more than 880,000 ocean-going vessels that broadcast their positions via AIS. Using precise latitude, longitude, and timestamp data from over 94 billion AIS messages we quantify near-real-time emissions for each vessel across three greenhouse gases (CO₂, N₂O, CH₄) and six other pollutants (PM_2.5, PM₁₀, NO_X, SO_X, CO, and VOCs). These emissions can be attributed to individual AIS pings, allowing us to link them to specific port visits and port-to-port trips. Our AIS-based emissions model is described in detail here.