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Aerial shot of container ships at Bangkok Port, Ratburana, Thailand.

Bangkok Port, Ratburana, Thailand. Container ships emit about one billion metric tons of CO2, which is three percent of global emissions, but the industry has set targets to completely decarbonize by 2050.

Credit: ProPIC / Getty Images

Maritime Shipping

Call to action:

Decarbonize the maritime shipping industry and reduce its environmental impacts by implementing changes throughout the supply chain of internationally traded goods.

Using giant container ships to ferry ninety percent of all consumer goods, the maritime transport industry is the backbone of the globalized economy. As global populations and economies grow, maritime trade volumes are set to triple by 2050. The sector accounts for three percent of the world’s greenhouse gas emissions and is projected to continue growing as demand increases. Large-scale change is needed across supply chains to reduce shipping emissions and pollution, including investment in low-to-zero carbon fuels and the vessels that can run on them. Retailers should prioritize maritime shipping over more emissions-intensive air freight and employ lightweight, streamlined packaging for their distributed goods. Individuals can do their part by shopping locally, or at least domestically, which cuts emissions from the shipping industry and the trucks, planes, and trains involved in the last leg of a product’s journey. Governments, port authorities, and shipping companies have responsibilities to transition to zero-carbon, low-impact shipping. Experts have mapped a pathway to decarbonize and minimize ecological harm over the coming decades, but enormous investment, innovation, and collaborative effort are required.

Action Items


Learn about the impacts of the maritime shipping industry. It is often overlooked that nearly everything we use daily – food, gas, clothing, and furniture – reaches us via a cargo freighter that travels for weeks across the sea. There are about 55,000 merchant ships that trade internationally, and in the past two decades, the size of an average container ship has doubled. Most run on bunker oil, the dregs of the petroleum refining process, and the dirtiest of fossil fuels. Maritime shipping currently burns about 300 million tons of this heavy fuel oil per year. In 2023, international agreements focused on reducing emissions in maritime shipping were signed, setting the industry on a trajectory towards achieving zero emissions by 2050. However, legally binding measures are needed to ensure goals are reached. Most emissions come from:

  • Ocean-going ships. Every year, container ships emit about one billion metric tons of carbon dioxide into the air. Most of these emissions are from the oil-based fuels that have historically accounted for over 99 percent of total energy for international shipping. Burning conventional ship fuel also produces sulfur oxide pollution, a known health and environmental hazard. In 2020, an international mandate capped the sulfur content of ship fuel, but the “scrubbers” that companies use to comply may have simply shifted the pollution from the air to the sea. It is the fuel itself that needs to change to minimize environmental and climate impacts. See Groups below to learn about the variety of renewable fuels and technologies in the works. Beyond emissions and air pollution, cargo ships can cause extensive ecological damage to marine environments due to contamination from sources such as bilge wastewater, which can contain human waste, chemicals, gasoline, and detergent. Other harm to wildlife comes from noise pollution, oil spills, and collisions.
  • Supply Chains. A key component of reducing greenhouse gas emissions in the shipping sector is decarbonizing the supply chain, which refers to all the systems involved in bringing a product to and from a ship, including land transportation.
  • Ports. This European Seaports Organization report divided port infrastructure into two categories. Terminal infrastructure includes docking areas, bunkering (refueling of vessels), and cold ironing (providing shoreside electric power to docked ships). Operational equipment consists of transport frameworks such as road and rail connections from the ports and within them, including cranes and tugboats. See more under Port Authorities below.

Do your part to reduce the emissions and impact of international shipping.

  • Shop locally or regionally and in bulk when possible. Consumer-to-consumer marketplaces make it easy to buy used items from local sellers, including large ones like eBay, Facebook Marketplace, OfferUp, and Craigslist. Some countries import more food than others, but no matter where we live, we can shift our diet toward locally and domestically grown, seasonal foods. These daily choices carry significant climate impact, as global food miles are responsible for about a fifth of all food systems emissions (see Localization Nexus). Consumers can buy locally-produced clothes (see Clothing Nexus) and prioritize purchasing domestic appliances and vehicles.
  • Learn about the environmental cost of next-day shipping. Typically, the faster we want our packages delivered to us, the more impact they will have. Consumer demand for same or next-day delivery makes companies prioritize speed over efficiency at a higher carbon cost. Choose the slowest delivery option whenever possible.
  • Reduce reliance on fossil fuels generally. By weight, they make up about 40 percent of all shipping cargo, so when we use less of them – for example, by driving an EV – we reduce the need for them to travel.

Pressure governments, shipping companies, and retailers to make changes. By importing goods to the U.S. in 2019 alone, fifteen retail companies (rated here) emitted as much climate pollution as the energy use of 1.5 million American homes. Some of the most influential retail giants include Home Depot, Amazon, Target, IKEA, and Walmart – currently the biggest polluter. Here are a few ways to get involved:

  • Ship It Zero is a coalition of shoppers, scientists, and environmentalists working to get some of the world’s largest retailers to commit to zero-emission shipping by 2030. They run targeted campaigns that consumers can support directly and promote action on the transition to renewable fuels and the reduction of port pollution.
  • At the freely accessible Global Shipping Watch dashboard, users can query data on the cargo and the emissions of companies, countries, and carriers.
  • See Governments below and demand your local lawmakers and officials prioritize policy change that supports maritime decarbonization.


Marine Scientists

Recommend ship routes that minimize harm to marine flora and fauna. Impacts include the pollution of water and air from exhaust, waste dumping and fuel and chemical spills, collision with marine fauna, invasive species from ballast water, and noise pollution. Research into the effects of ship traffic is often categorized by type of impact, but scientists suggest there is potential benefit from a more holistic approach to studying and managing them.

  • Biofouling is the contamination of underwater environments via surfaces colonized with microorganisms and bacteria, causing corrosion, increased fuel and energy consumption, increased hydrodynamic weight of ships, and higher frictional resistance. It is commonly treated with toxic chemicals that harm marine environments, but a biomimicry-based solution drawn from the design of seabird feathers is in development.


Accelerate the deployment of emissions-reducing shipping technologies. The industry is not currently on target to meet its ambitious goals, which means a significant push is needed in the level of effort and investment to quickly bring the most promising innovations to market. Along with initiatives to improve the deployment of the renewable energy infrastructure described above, opportunities exist for research and development related to:

Port Authorities

Develop onshore power systems for use by docked ships. Connecting ships to shoreside electricity, known as cold ironing, can potentially eliminate emissions in ports with significant ecological and climate benefits.

Provide facilities for electric ships to plug in and recharge their batteries. Ports can make use of the fast-evolving energy storage and charging innovations currently available, including offshore charging buoys.

Develop renewable energy infrastructure. Seaports play a critical role in driving renewable energy development and are ideal locations for offshore renewable technologies, including wave and tidal energy (see Nexus), offshore wind, and floating offshore wind. They are also considered prime sites for green hydrogen infrastructure.

Implement port design and procedures that protect environmental quality.

  • Minimize noise. The negative impacts of underwater noise on marine life and ecosystems are acute, chronic, and cumulative. Ports can incentivize acoustic controls through measures such as discounted port fees and reduced ship waiting time. They can also invest in construction technologies such as “bubble curtains,” which can be used to absorb noise from in-water activities.
  • Provide waste disposal and recycling facilities. This policy brief on managing port and shipping waste describes best practices, which have evolved away from disposal at sea and toward land-based systems with improved efficiency, better segregation of items, and more recycling.
  • Execute sustainable sediment-management practices. The process of dredging waterways and ports has a carbon footprint that can be reduced via specific practices and materials, including the use of clay and updated equipment. There is also potential for containing the organic carbon in dredged soil and utilizing it as foundational materials for blue carbon ecosystems with sequestration value.

Investors and Financial Institutions

Fund the transition to green shipping. A 2022 report identifies vital “asks” for lenders and investors to make of shipping providers and service users. Funders can engage with portfolio companies around the massive financing required globally in alternative infrastructure and technologies.

  • Invest in the blue bond market by purchasing sustainable debt instruments issued by governments, development banks, and other institutions to raise capital for marine projects with environmental, economic, and climate benefits, including shipping.


Shipping Companies

Go slower. Reducing the speed of shipping vessels, called “slow steaming,” reduces the amount of fuel burned per ton-mile. According to some estimates, cutting speed by twenty percent can reduce a ship’s carbon emissions by 24-37 percent, slash air pollution by up to a third, and underwater noise pollution by two-thirds. At the same time, lowering speed saves money, prevents oil spills and accidents, and reduces noise pollution, making it safer for whales and workers alike. See Governments below on how “Blue Speeds” are being integrated into policy, with the European Union playing a leading role.

Decarbonize your shipping fuels. Life cycle assessment methodology involves well-to-wake analysis (from fuel production to burning), breaking out well-to-tank emissions and tank-to-wake emissions. This in-depth assessment is the first step to developing an implementation program for the uptake of alternative fuels. The International Maritime Organization is developing Life Cycle Assessment Guidelines on the emissions intensity of various fuels that are expected to be released in late 2023.

  • Green hydrogen is the only hydrogen fuel produced in a climate-neutral manner, making it a critical piece of decarbonizing maritime shipping. Green hydrogen and ammonia require further acceleration of the deployment of renewable electricity, but as costs fall both for green energy and the electrolyzers used to split hydrogen from water, it is projected that green hydrogen will become cost-competitive from around 2030. See Green Hydrogen Nexus.
  • Sulfur-free fuels such as methanol and ammonia have been considered by the industry following the implementation of the International Maritime Organization sulfur cap. This 2020 regulation limited the amount of sulfur that can be emitted by ships to 0.5 percent in an effort to reduce air pollution. Methanol and ammonia emissions are free of sulfur, thus safer for marine life, but some types are associated with other types of greenhouse gas emissions. Green/Renewable methanol is synthesized using green hydrogen and renewable energy, has the advantage of being retrofit-capable for traditional four-stroke engines, and has the potential to be carbon neutral. Production is currently constrained by energy costs and safety issues, but promising technologies are developing, and production is being expanded on several continents. Green/renewable ammonia production is also growing, particularly in Asia.
  • Advanced biofuels (avoiding those that use food crops) can be immediately utilized by the shipping industry, resulting in significant emissions reductions. Blending these with conventional fuels at twenty to thirty percent is possible without engine modifications. Read more here about the use of biofuels in international shipping.

Harness the wind. Major shipping companies are collaborating to return clean, quiet, and free wind power to cargo freighters, testing ways that various types of sails can be retrofitted to conventional ships to slash their greenhouse gas emissions and reduce other environmental impacts.

Reduce and efficiently manage waste. Ships generate a large amount of various types of waste and are required to have a Garbage Management Plan. The first step is to minimize waste by efficient operational and dining planning that reduces food waste, sludge and packaging, and recycling whenever possible.

  • These tips for reducing and recycling waste at sea include the creation of systems for categorizing and storing various types of waste such as plastics, batteries, food waste, chemicals, and adhering to zero-dumping policies. Waste can be compacted when appropriate, and common recycling bins are made available; items such as paper and cardboard can often be reused onboard.

Be cautious about using scrubbers since they only shift the pollution to the seas. Scrubbers are intended to remove sulfur oxide pollution from ship exhaust, but the impact of the discharge water they produce contributes to ocean acidification. This has led to them being restricted in many locations, and they will likely be phased out in the long term. This article describes the various types of scrubbers, some cleaner than others, and why they fail as an effective climate solution.

Properly maintain cargo vessels to avoid oil and chemical spills. Companies can prevent oil leakage and other pollutants through proper maintenance, such as replacing loose fittings and hydraulic lines and the installation of oil absorbents and/or drip pans. A Spill Prevention, Control and Countermeasure Plan can be put in place to prevent migration of oil and other pollutants into waterways.

Dismantle out-of-commission ships safely and in compliance with environmental regulations and recycle as much as possible. Ship scrapping is heavily polluting and can expose workers and environments to toxic materials when done improperly. The U.S. Environmental Protection Agency published tips for regulatory compliance in this Guide for Ship Scrappers, including information about removing asbestos, polychlorinated biphenyls, bilge and ballast water, paint, metal, oil, and fuel.

Update your shipping fleets with next-generation vessels. This can include purchasing newly-designed ships and/or retrofitting current ones with emissions-reducing technologies. Maersk has led the major corporations by ordering nineteen vessels that can operate on green methanol and setting a zero-emissions target for 2040. Oil spills can be prevented by using double-hulled vessels or ships with enhanced oil spill prevention systems. The market for electric-powered shipping vessels is projected to grow exponentially over the coming decade. Consider adding them to your fleet.


Localize your supply chain. Localization has multiple benefits, and demand for local products is increasing, accelerated by the pandemic. Retail giants like Target and Kohl’s have rolled out plans to accelerate localization, tailoring stores to the surrounding community.

Encourage customers to choose shipment options that reduce emissions. Online stores can promote the prioritization of bulk shipment, streamline and use lightweight packaging, and offer incentives for slower delivery or local pickup. Educating consumers on the carbon impacts of different shipping options can significantly affect behaviors.

Commit to transitioning your ocean freight to zero-emission vessels. Cargo Owners for Zero Emission Vessels (COZEV) is an initiative that brings companies together to raise ambitions for the decarbonization of shipping. A growing number of large retailers have signed on to accelerate demand, committing to switch all shipping vessels to those run on zero-carbon fuel by 2040.


Provide economic incentives to scale up reduced-emissions vessels and renewable shipping fuels. The International Chamber of Shipping has proposed a sector-wide tax that shipping companies pay per ton of marine fuel, funding research and development of next-generation vessels. And since newer green fuels are two to three times more expensive than fossil fuels, regulators need to negotiate with stakeholders on an international level to employ market-based policies to incentivize the use of the fuels most essential for decarbonizing, such as green hydrogen. See the Governance section of the Green Hydrogen Nexus for more on this.

  • A global carbon levy assigns fuels a carbon price that adjusts over time as the market for renewable energy fuels improves. Polluting industries can purchase and sell emissions permits, an approach that can be combined with programs to “buy down” low-emissions fuels. This lowers the cost of green fuels for shipping companies and effectively levels the playing field between conventional and green vessels. These initiatives facilitate companies getting low-to-zero emissions ships on the water and operating them competitively.

Implement comprehensive “command and control” policies to ensure shipping sector emissions are reduced in alignment with international climate goals.

  • A mandatory speed limit, differentiated by vessel type, is an effective way to promote ‘Blue Speeds’: ship speed levels that reduce emissions and have co-benefits for marine life and humans.
  • Develop and enforce shipbuilding standards that support the energy transition. These could include restricting the construction of vessels that operate on fossil fuels alone beyond a specific date or requiring ships built after a set deadline to have greener fuel capacity. This transition will require additional construction and retrofitting, making it essential to set environmental standards for the energy-intensive shipbuilding industry.

Establish international green shipping corridors. Green corridors have been recognized as a critical enabler for shipping’s transition, mobilizing the creation of specific trade routes between major port hubs where zero-emissions infrastructure is supported. They involve targeted regulatory measures and financial incentives to boost demand for green shipping on particular routes and have spillover effects that accelerate decarbonization on other corridors.

  • Become a member of the International Maritime Organization (IMO) Green Corridors Program, scaling up zero-emissions ships and fuels across trade lanes where the necessary shoreside energy infrastructure is first available. Twenty-two nations have signed the Clydebank Declaration, founding the initiative as a step towards aligning the shipping industry with climate goals. Signatories agreed to the establishment of six completely decarbonized maritime routes by 2025. The pilot corridors will then be lengthened, with more routes and vessels added.
  • Maersk partnered with progressive ports to establish the European Green Corridors Network to demonstrate how early commercialization of alternative fuel supply chains can provide a blueprint for rolling out green corridors in other locations. Additional public and private stakeholders will be onboarded, activating the full value chain needed to realize the vision.

Facilitate a more equitable transition by accounting for a nation’s level of development and historic contribution to climate change. The Initial IMO Greenhouse Gas Strategy recommended assessing and addressing situations where the transition may disproportionately affect certain member-states. For small island nations with high shipping costs, it is essential to chart an equitable, affordable course for green shipping corridors that builds port infrastructure resilience.

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