Great Lakes-St. Lawrence Seaway¶
The System¶
The Great Lakes-St. Lawrence Seaway (GL-SLS) is a single, interconnected emissions landscape. The same domestic "Laker" fleet calls at port after port, loading iron ore in Duluth, dropping it at Cleveland, returning empty for the next cycle. Bulk commodity logistics — iron ore, coal, grain, limestone — mean vessels spend 24–72 hours at berth running auxiliary diesel engines, generating concentrated at-berth emissions that disperse into the working-class communities adjacent to every terminal in the system.
110 ports in the GL-SLS system
953 vessels identified in the 2019 ICCT inventory
1.6 Mt CO₂ emitted from GL-SLS vessels (2019)
ZERO U.S. Great Lakes ports with mandatory at-berth controls
Sources: ICCT, "Greenhouse gas and air pollutant emissions from ships in the Great Lakes-St. Lawrence Seaway region" (Meng & Comer, March 2022); ICCT, "Nationwide port emissions screening for berthed vessels" (September 2024); ICCT/MARAD, "Feasibility study of future energy options for Great Lakes shipping" (March 2024).
System-Level Footprint¶
| Metric | 2019 GL-SLS Total |
|---|---|
| Ports | 110 |
| Vessels | 953 |
| Cargo moved (2017) | 143.5 million tonnes ($15.2 billion value) |
| CO₂ from vessels | 1,600,000 tonnes |
| NOx from vessels | 32,000 tonnes |
| PM2.5 from vessels | 813 tonnes |
| VOCs from vessels | 1,200 tonnes |
Why these numbers matter. The entire GL-SLS system has been inside the North American Emission Control Area (ECA) since 2013, which capped fuel sulfur content for vessels operating in the region. The ECA addresses underway emissions while ships are moving — it does not address auxiliary engine emissions while ships sit at berth running generators for power, refrigeration, and loading equipment. At-berth emissions remain entirely uncontrolled across all 110 ports.
Why the system frame matters. Approximately 90% of Duluth-Superior traffic is domestic Lakers — the same Great Lakes freighters that call at Two Harbors, Silver Bay, Cleveland, Toledo, Burns Harbor, and dozens of other ports across the system. Emissions reductions at any one port are diluted unless paired with system-wide adoption of at-berth controls.
Key Data Sources¶
| Source | Publisher | Coverage |
|---|---|---|
| GL-SLS Ship Emissions Inventory | ICCT (March 2022) | 953 vessels, all GL-SLS ports, 2019 inventory year |
| Nationwide Port Emissions Screening | ICCT (September 2024) | 129 U.S. ports, at-berth emissions, priority categorization |
| Future Energy Options Feasibility Study | ICCT/MARAD (March 2024) | Alternative fuels, shore power feasibility, port profiles |
| EJScreen | EPA | Census-tract environmental justice indicators |
| CDC PLACES | CDC | Census-tract health estimates (asthma, COPD, cardiovascular) |
| Waterborne Commerce Statistics | USACE | Port tonnage and vessel movements |
Priority Ports¶
The eight U.S. ports below were selected for their combination of cargo volume, vessel call intensity, community exposure profile, and regulatory standing. Duluth-Superior is the deep-assessment anchor; the remaining seven are screening-level profiles that document what a full assessment would quantify.
| Port | State | Annual Tonnage | Primary Cargo | Regulatory Jurisdiction | At-Berth Controls | Assessment Status |
|---|---|---|---|---|---|---|
| Duluth-Superior | MN / WI | 25.3M | Iron ore, coal, grain, limestone | MN PCA, WI DNR, EPA Region 5 | None | Full Assessment |
| Two Harbors | MN | ~13M (est.) | Taconite/iron ore | MN PCA, EPA Region 5 | None | Screening |
| Silver Bay | MN | ~5M (est.) | Taconite | MN PCA, EPA Region 5 | None | Screening |
| Green Bay | WI | ~2M (est.) | Paper, petroleum, coal, salt, limestone | WI DNR, EPA Region 5 | None | Screening |
| Milwaukee | WI | ~2.5M (est.) | Bulk, breakbulk, liquid, container | WI DNR, EPA Region 5 | None | Screening |
| Cleveland | OH | ~13M (est.) | Iron ore, limestone, steel, general | Ohio EPA, EPA Region 5 | None | Screening |
| Toledo | OH | ~10M (est.) | Coal, iron ore, grain, petroleum | Ohio EPA, EPA Region 5 | None | Screening |
| Indiana-Burns Harbor | IN | ~2.5M (est.) | Iron ore, steel, limestone | IDEM, EPA Region 5 | None | Screening |
The "At-Berth Controls" column reads "None" in every row. That is the point.
The Regulatory Gap¶
No Great Lakes port has mandatory at-berth emissions controls.
All eight priority ports sit in EPA Region 5 states (Minnesota, Wisconsin, Ohio, Indiana). All are eligible for the Great Lakes Environmental Justice Thriving Communities Grantmaking Program ($52 million administered by the Minneapolis Foundation, rolling applications through November 2026).
California's CARB At-Berth Regulation has been in effect since 2014 and was strengthened in 2020. In October 2023, the EPA authorized California's regulation under the Clean Air Act, which legally enables any other state to adopt the identical standard. No Great Lakes state has done so. Minnesota, Wisconsin, Ohio, and Indiana each have independent legal authority to act; none have moved.
The MERC coal terminal closure on June 30, 2026 — covered in the Duluth-Superior assessment — eliminates approximately 8,500 tonnes CO₂/year of port-attributable emissions in a single regulatory event, and creates a clean before/after monitoring window that no policy intervention has been able to deliver.
From Screening to Full Assessment¶
This section uses a two-level methodology.
Screening profiles (this hub and the seven linked subpages) draw on publicly available data — ICCT GL-SLS inventory, ICCT port screening, EPA EJScreen, CDC PLACES, USACE Waterborne Commerce Statistics, U.S. Census ACS — and where appropriate, scale estimates from Duluth-Superior's fully characterized profile based on relative tonnage and vessel call counts. Scaled estimates are labeled as such throughout. Screening profiles do not produce monetized health impact figures.
Full site-specific assessments — like the Duluth-Superior deep assessment — add census-tract-level health impact quantification using BenMAP-CE methodology, FOIA-enhanced public records data across federal and state frameworks, regulatory pathway mapping, and advocacy-ready deliverables. Health damages are quantified using EPA Value of Statistical Life and concentration-response functions. See our Services page for engagement options and pricing.
The Duluth-Superior Anchor¶
The Port of Duluth-Superior is the system's deep-assessment anchor. Three properties make it uniquely valuable as a proof-of-concept site:
- Largest GL port by tonnage (25.3M tons in 2025), with 687 vessel calls and a fully characterized Scope 1/2/3 emissions inventory drawn from the Duluth Seaway Port Authority's 2024 Climate Action Plan.
- Cross-state jurisdiction spanning Minnesota and Wisconsin — exactly the regulatory complexity the rest of the GL system would face under any multi-state harmonization effort.
- MERC coal terminal closure on June 30, 2026 — the cleanest natural experiment in Great Lakes port emissions available this decade. Pre-closure FOIA-driven baseline collection is underway; post-closure ambient monitoring will validate the dMRV methodology that any system-wide credit framework would depend on.
A monitoring methodology proven at Duluth — particularly one validated through the MERC before/after window — is directly portable to every other priority port in this section. Read the full Duluth-Superior assessment →.
Last updated: April 2026
Data sources: ICCT GL-SLS Ship Emissions Inventory (Meng & Comer, 2022); ICCT Nationwide Port Emissions Screening (September 2024); ICCT/MARAD Feasibility Study of Future Energy Options for Great Lakes Shipping (March 2024); EPA EJScreen; CDC PLACES; EPA ECHO; USACE Waterborne Commerce Statistics; U.S. Census ACS.