The impact of GHG emissions in shipping: an overview

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impact of ghg emissions in shipping

Shipping plays a vital role in global trade, yet it also makes a substantial contribution to greenhouse gas (GHG) emissions. Gaining insights into the causes and impacts of these harmful gases released during international sea transportation is crucial for developing and implementing effective strategies to mitigate their adverse effects. This, in turn, fosters a pathway toward a more sustainable future for our planet.

What are the causes of GHG emissions from international shipping?

Greenhouse gas (GHG) emissions refer to the release of specific gases (carbon dioxide, methane, nitrous oxide, and fluorinated gases), into the Earth’s atmosphere. These gases create a greenhouse effect, trapping heat and resulting in the accumulation of warmth that contributes to global warming the planet and climate change. The heightened concentration of these gases in the atmosphere is predominantly attributed to human activities such as agriculture, deforestation, the combustion of fossil fuels for energy, industrial processes, and various modes of transportation—whether by air, road, or sea.

Concerning the global shipping industry, the environmental impact is multifaceted, with various factors contributing to the sector’s GHG emissions. Understanding the root causes is crucial for developing comprehensive strategies aimed at fostering sustainability and mitigating the ecological footprint of the shipping sector.

Fossil fuel dependence

The global shipping industry heavily depends on conventional fuels as their primary energy. Most large ocean-going vessels, including container ships, bulk carriers, and oil tankers, traditionally use heavy fuel oil (HFO) or marine diesel oil for their main propulsion. Additionally, ships employ diesel fuel for the auxiliary engine, which powers essential systems like electricity generation, pumps, and navigation equipment. However, the combustion of HFO releases substantial amounts of carbon dioxide (CO2), sulfur oxides, and other pollutants into the atmosphere.

fossil fuel dependence is a cause of ghg emissions

Operational factors

The operational practices of shipping companies, including ship speed and routing, influence fuel consumption and emissions. Opting for slower speeds and more efficient routes can contribute to a significant reduction in overall carbon footprints. Furthermore, older large vessels equipped with less efficient engines, and propulsion systems may increase fuel consumption and emissions in comparison to their newer, more energy-efficient counterparts.

Higher energy demand for some cargo and vessel types

Cruise ships and specific passenger vessels have higher energy demands due to amenities like air conditioning, lighting, and entertainment systems. Likewise, certain cargo categories, including refrigerated containers and bulk carriers, necessitate additional energy for climate control or specialized handling, leading to elevated emissions. As a result, carrying them may produce more significant greenhouse gas (GHG) emissions.

Environmental impact of spills and accidents

Accidents and spills, such as oil spills from shipping vessels during maritime transport, can have severe environmental consequences, harming the marine fauna and flora, ecosystems, and coastal areas.

Lack of regulation

While some international regulations exist to limit ship emissions, they are often weak and inconsistently enforced. This lack of stringent regulations hinders effective emission reduction efforts.

oil spill is a cause of ghg emissions

What are the impacts of air pollution from ships?

The intricate relationship between maritime activities and environmental consequences is a pressing concern that extends beyond the world’s oceans.

Contribution to climate change

The combustion of fossil fuels by merchant vessels releases carbon dioxide (CO2), a major greenhouse gas contributing to global warming and climate change. Shipping is responsible for approximately 3% of global CO2 emissions. Beyond CO2, the sector contributes to other harmful gases such as methane (CH4), nitrous oxide (N2O), and black carbon. Although these gases constitute a smaller portion of total emissions, they intensify the greenhouse effect, leading to global warming, rising sea levels, extreme weather events, and other climate-related impacts.

Air pollution

Emissions generated by shipping activities contribute to air pollution in coastal areas and port cities, and can be transported inland, impacting human health. Particulate matters (PM), sulfur oxides (SOx) and nitrogen oxides (NOx) can produce acid rain, exacerbate respiratory diseases and other illnesses.

air pollution from ships can cause ocean acidification

Ocean acidification

The excess CO2 emitted by ocean transportation and other activities associated with the maritime sector is not only absorbed by the air but also by the waters. This process results in sea acidification, which can have adverse effects on marine ecosystems, exacerbating issues related to water pollution. Species relying on calcium carbonate-based structures, such as coral and shellfish, are especially vulnerable. The repercussions extend to marine mammals and fish, impacting biodiversity and disrupting the delicate equilibrium of aquatic environments. On a broader scale, there is a potential threat to food security.

What are the solutions to mitigate GHG emissions from shipping?

The International Maritime Organization (IMO), which regulates the sector, acknowledges the necessity of addressing the environmental consequences associated with maritime freight transport. Therefore, it has shifted its focus toward attaining net-zero emissions for the sector by approximately 2050 and contributing to achieving the Paris Agreement goals. Its initial strategy aims at cutting the total annual GHG emissions by at least 50% by this deadline, compared to 2008 levels.

Hand in hand, member nations, and maritime industry stakeholders are deploying a collective effort toward a cleaner future. The roadmap to achieve this ambitious goal encompasses a range of initiatives:

Developing renewable energy sources

Increasingly, shipbuilders and shipping companies turn to renewable energy sources for the propulsion of merchant vessels. Wind power contributes further to the propulsion, while solar panels supply green electricity for various on-board facilities.

Switching to emerging alternative fuel

Liquefied Natural Gas (LNG) is considered as a cleaner alternative to conventional, highly polluting fossil fuels. It generates lower carbon dioxide (CO2) emissions and diminishes sulfur oxide and particulate matter emissions. However, it is essential to note that LNG is not entirely carbon-neutral, and its widespread adoption in the shipping industry remains limited. Simultaneously, there are ongoing efforts to explore and embrace carbon-neutral alternatives such as biofuels (methanol and ammonia) and hydrogen to further reduce the carbon footprint of shipping.

For energy storage, particularly on short sea routes, battery-electric or hybrid systems are viable options. Furthermore, electric propulsion can be facilitated through the utilization of hydrogen fuel cells.

Promoting energy-efficiency designs and practices

Ocean-going vessel designs and equipment have evolved to enhance their energy efficiency. The optimization of hull shapes and the application of specialized coatings to reduce friction enable higher propulsion and lower energy consumption.

Besides, the adoption of slow steaming has become a prevalent practice. It consists of operating cargo ships at speeds under their maximum capabilities. This allows for a reduction in both fuel consumption and greenhouse gas emissions.

Last, training is provided to seafarers and shipping professionals, to encourage them to maximize the use of sustainable practices and eco-friendly technologies.

importance of technological advancements to mitigate ghg emissions

Leveraging technological advancements

The integration of data and maritime intelligence heralds a new era. Shipping companies employ data analytics to optimize routes, speeds, and logistics operations for each vessel in their fleet, with a focus on minimizing energy consumption for every nautical mile sailed. On board, a suite of intelligent sensors enables real-time monitoring of engines and other critical features. Adaptive algorithms, powered by artificial intelligence and machine learning, process the gathered data, facilitating informed decision-making and enhancing overall energy management.

Implementing incentive schemes

Businesses and organizations should be encouraged to invest in carbon offset projects as a way to offset the pollution generated by their activities. In this context, governments can provide financial incentives, such as subsidies or tax breaks, to companies that embrace low-carbon technologies and fuels.

Additionally, implementing a pricing mechanism for carbon emissions can serve as an incentive to further cut emissions from shipping and other economic sectors via Emissions Trading Systems. ETS is a market-based approach designed to control and reduce greenhouse gas emissions. It operates on the principle of setting a cap on the total amount of certain GHG that can be emitted by covered entities, such as industrial facilities or power plants. These entities are issued emission allowances corresponding to the cap.

The system allows entities with emissions below their allocated allowances to sell their excess allowances to those exceeding their limits. This creates a financial incentive for companies to reduce their emissions efficiently, as they can benefit from selling unused allowances.

The best-known example of an Emissions Trading System is the European Union Emissions Trading System (EU ETS), established by the European Union to regulate carbon dioxide emissions from power stations and industrial facilities. Other countries and regions have also implemented similar systems, demonstrating their will to address climate change and reduce overall greenhouse gas emissions.

Enforce regulation

As of January 2023, the International Maritime Organization has initiated a set of new obligatory measures designed to improve vessel efficiency. The Energy Efficiency Existing Ship Index (EEXI) and the Carbon Intensity Indicator (CII) aim to monitor and report emissions from new ships. As for existing vessels, compliance involves documenting their energy usage through the implementation of the Ship Energy Efficiency Management Plan (SEEMP), which is seamlessly integrated into their comprehensive management plan. These IMO programs, approved by the Marine Environment Protection Committee (MEPC) in July 2011, aim to cut down GHG emissions from international shipping and amend MARPOL Annex VI Regulations.


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Strengthening collaboration among stakeholders

Promote cooperation between all the stakeholders throughout the entire value chain, encouraging the sharing of knowledge, best practices, and sustainable innovations. Industry collaborations, government partnerships, and international agreements are avenues through which this objective can be accomplished.

Google Scholar fosters collaboration and information sharing globally, further contributing to sustainability efforts. This digital platform provides easy access to millions of academic publications online, with features like citation analysis and related articles to help researchers find relevant scholarly articles and publications quickly, and with minimum environmental impact.

Electrifying ports

Enable ships to switch off their engines while docked by offering shore power at ports, thereby reducing emissions.


Given the ongoing growth of global trade, the maritime sector remains crucial for delivering goods and fueling economies. Nevertheless, beneath the surface lies a significant challenge in the form of the ecological footprint associated with activities at sea. Ignoring this hidden cost is no longer an option. The industry must confront this hidden cost and transition from being a polluter to becoming a protector of the planet. This requires immediate action on multiple fronts.

Frequently Asked Questions about GHG Emissions

GHG emissions in shipping arise from fossil fuel dependence, operational factors, higher energy demand for specific cargo and vessel types, environmental impacts of spills and accidents, and a lack of stringent regulations.

Air pollution from shipping contributes to climate change, with emissions such as carbon dioxide (CO2), methane (CH4), nitrous oxide (N2O), and black carbon.

It also leads to air pollution in coastal areas and port cities, causing health issues and ocean acidification with adverse effects on marine ecosystems.

Solutions include developing renewable energy sources, switching to alternative fuels like LNG, promoting energy-efficient designs and practices, leveraging technological advancements through data analytics and AI, implementing incentive schemes, enforcing regulations, and electrifying ports.

The IMO aims to achieve net-zero emissions for the sector by 2050, with a strategy to cut total annual GHG emissions by at least 50% by 2050 compared to 2008 levels.

It has introduced measures like the Energy Efficiency Existing Ship Index (EEXI), the Carbon Intensity Indicator (CII), and the Ship Energy Efficiency Management Plan (SEEMP) to monitor and reduce emissions

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