Maritime decarbonization is the process of reducing greenhouse gas (GHG) emissions from the global maritime sector, with an overall goal of placing the sector on a pathway that limits global temperature rise to 1.5-degrees Celsius.

The maritime industry is at the onset of a once-in-a century energy transition as it looks for ways to decarbonize rapidly through electrification and low-carbon fuels, optimization tools, and efficiency technologies.

The U.S. government has committed to ambitious goals for maritime emissions reduction which will require the resources and expertise of the numerous federal agencies working in concert. The U.S. Department of Energy and its National Laboratory system have important roles to play in this work, especially on research, development, and demonstration.

This page includes links to maritime relevant work across the U.S. Department of Energy and its National Laboratories across several technological focus areas, including: low-carbon liquid and gaseous fuels; hybridization and all-electric drive trains; energy efficiency and optimization; and exhaust treatment and carbon capture.

What is the Maritime Industry?

The maritime industry is the international network of ships and ports that makes the global economy possible. The ships responsible for this mass movement of goods are some of the largest machines on earth, powered and propelled by some of the largest engines.

The maritime shipping industry also includes numerous types of smaller vessels, such as ferries, tugs, and trawlers that navigate coastal and inland waterways. Vessels interface with land transportation modes like trucks and rail at seaports and harbors, thereby allowing cargo to reach destinations further inland.

In the U.S., there are approximately 40,000 commercial vessels and 360 commercial seaports handling every type of cargo, from people to phosphorus. There are an additional 10.5 million motorized recreational boats.

Shipping is hard to decarbonize due to the wide spectrum in vessel types and sizes, the large amounts of energy they use, and the inherently global nature of maritime transport that necessitates working across geographies.

Why is Maritime Decarbonization Important?

Ports and ships need vast amounts of energy for cargo-handling equipment, ground transport, electricity generation, and vessel propulsion. Global emissions from all vessels account for about 3% of total GHG emissions each year; if the maritime industry was its own country, it would rank sixth on the list of largest GHG emitters globally.

Maritime transport activities also produce criteria pollutants, accounting for 9% of sulfur oxides (SOx) and 18% of nitrogen oxides (NOx) emissions annually. Due to the natural confluence of activities from vessels, trucks, cargo-handling equipment, and railcars in the seaport complex, these areas often experience higher concentrations of GHG emissions.

About 12% of the U.S. population lives near seaports, many of whom reside in port-impacted communities that exhibit higher rates of respiratory and cardiovascular disease, dangerous soil and water quality, and poorer health outcomes exacerbated by these elevated emissions.

There are multiple pathways that would deliver emissions reductions for the maritime sector, including low-carbon liquid and gaseous fuels; hybridization and all-electric drive trains; clean energy, energy efficiency, and optimization; and exhaust treatment and carbon capture.

What is DOE Doing for Maritime Decarbonization?

There are many different technologies, tools, and fuels that can reduce maritime emissions. Some are commercially available, while others are still nascent and in need of additional research and development.

DOE works across this entire spectrum, often in partnership with other agencies like the U.S. Department of Transportation, Maritime Administration (MARAD), Coast Guard, Environmental Protection Agency, and Navy.

Maritime Decarbonization Activities

Below are some examples of some of the maritime activity areas that DOE is supporting. For active funding opportunities, please visit or consult the EPA’s Ports Initiative Funding Opportunities for Ports and Near-Port Communities.

These activities fall under the following categories—use the pivot table below to find specific activities in each category:

Low-Carbon Liquid and Gaseous Fuels

These fuels, also referred to as sustainable marine fuels, are a recognized pathway for lowering GHG emissions compared to heavy fuel oil and other petroleum-based marine fuels. More detail on sustainable marine fuels is found on this webpage from the Bioenergy Technologies Office.

Hybridization and All-Electric

Most non-fossil fuel engine propulsion systems being considered by the maritime industry are based on an electrified (instead of mechanical) powertrain. Electric-based powertrains may be a way to help future-proof vessels as new technologies become available over a ship's 30 year or more operating life. Moreover, integrating marine engines with hybrid technology could also offset fuel consumption and reduce emissions.

Energy Efficiency and Optimization

Energy efficiency is concerned with getting the most out of energy inputs (i.e., fuel) by reducing losses in conversion. The conversion of chemical energy in a fuel to mechanical energy for propulsion involves numerous energy losses along the way, which present opportunities for improvement (see Figure 18). Some of the major energy efficiency improvements that can be made to vessel machinery through waste heat recovery, optimizing designs of vessel equipment and auxiliary machinery, and shipboard power management systems.

Exhaust Treatment and Carbon Capture

Exhaust gas emissions from maritime transportation are of increasing environmental concern, and existing emissions treatment strategies will require renewed R&D attention to address new challenges introduced by the advent of novel fuel and propulsion technologies.

Topic Area

International Collaborations

  • Mission Innovation Zero-Emission Shipping Mission—An international PPP the U.S. is co-leading to address the innovation gaps slowing the adoption of zero-emission fuels for ocean-going vessels.
  • Mission Innovation Clean Hydrogen Mission—An international PPP the U.S. is co-leading to accelerate the building of a global clean hydrogen economy by reducing end-to-end clean hydrogen costs to $2 per kg by 2030. 
  • First Movers Coalition—An international voluntary program that is triggering demand within key industries (including maritime) to make emerging clean technologies accessible and scalable
  • Marine Battery Forum—DOE participates as an observer in this international forum on maritime vessel electrification.
  • International Energy Agency—Organizes several technology collaboration protocols through which the DOE collaborates with other international stakeholders on R&D needs.

Other Federal Agencies and Offices Engaged on Maritime Decarbonization