Shipping carbon dioxide (CO2) emissions are a significant environmental concern, stemming from the global movement of goods by sea. Maritime transport is the backbone of international trade, facilitating the movement of vast quantities of raw materials and finished products across oceans. This extensive activity contributes to greenhouse gas emissions, impacting global climate patterns.
Understanding Shipping Emissions
The international shipping industry contributes approximately 2% to 3% of global energy-related CO2 and greenhouse gas emissions annually. For example, in 2022, international shipping alone accounted for nearly 3% of the world’s total greenhouse gas emissions. This sector relies on fossil fuels, such as heavy fuel oil, consuming around 5% of global oil production to power vessels across vast distances. The combustion of these fuels releases CO2, along with other gases like methane and nitrous oxide, and harmful particulate matter.
Container ships, oil tankers, and bulk carriers are the primary contributors to these emissions, collectively accounting for nearly 80% of the CO2 emitted by international shipping. The carbon intensity of these vessels is influenced by factors such as ship type, size, fuel consumed, and deadweight capacity. Without substantial changes, the carbon footprint from shipping could increase by 50% to 250% by 2050.
Global Efforts to Reduce Emissions
The International Maritime Organization (IMO), a specialized agency of the United Nations, plays a central role in regulating maritime transport and preventing pollution. One significant measure implemented was the IMO 2020 sulfur cap, which reduced the permissible sulfur content in marine fuel from 3.5% to 0.5% as of January 2020. This aimed to lessen sulfur oxide emissions and improve air quality.
Building on these efforts, the IMO adopted a revised Greenhouse Gas (GHG) Strategy in 2023, aiming for net-zero GHG emissions from international shipping by or around 2050. This strategy includes targets such as reducing carbon intensity by at least 40% by 2030 compared to 2008 levels. It also aims for at least 5% of the energy used by international shipping by 2030 to come from zero or near-zero GHG emission technologies and fuels.
To support these goals, the IMO introduced mandatory measures effective January 1, 2023, incorporated into MARPOL Annex VI. The Energy Efficiency Existing Ship Index (EEXI) requires existing ships to demonstrate their energy efficiency based on technical specifications. The Carbon Intensity Indicator (CII) assesses a ship’s operational carbon intensity, linking GHG emissions to cargo carried over distance traveled. Ships receive an annual rating from A (good) to E (poor), with a minimum C rating required. Vessels receiving a D rating for three consecutive years or an E rating for one year must submit a corrective action plan.
Technological Solutions and Operational Changes
Decarbonizing shipping involves technological advancements and operational efficiencies. Improvements in vessel design enhance energy efficiency through better hydrodynamics, including optimized hull and propeller designs and air lubrication systems. Waste heat recovery systems and wind-assisted propulsion also contribute by harnessing lost energy or natural forces to reduce fuel consumption. These design enhancements help lower the energy demand of ships.
The shift towards alternative fuels represents a significant pathway for emission reduction. These include:
- Liquefied Natural Gas (LNG): A low-carbon fuel for short-term CO2 reductions, though not zero-emission.
- Methanol and Ammonia: Methanol engines are cost-effective, and ammonia, if produced from renewable energy, offers a carbon-free option.
- Hydrogen: A carbon-free fuel with potential for long-term zero-carbon shipping, especially with fuel cells, but faces cost and readiness challenges.
- Biofuels: Biodiesel and renewable diesel can reduce lifecycle emissions by up to 90% and require minimal vessel retrofitting, but scalability is a concern.
- Shore Power Systems: Allow vessels to connect to land-based electricity while docked, significantly reducing emissions in port areas.
Operational changes complement technological solutions by optimizing existing fleet performance. Slow steaming, reducing a vessel’s speed, directly lowers fuel consumption and emissions. Route optimization, leveraging weather routing and real-time data analysis, helps ships navigate efficient paths, avoiding adverse conditions and conserving fuel. Other practices, such as optimizing a ship’s draft and trim, also contribute to improved operational efficiency and reduced carbon intensity.