International Aviation and Shipping Emissions

Introduction

International aviation and maritime shipping together account for approximately 5% of global greenhouse gas emissions, a proportion that is rising as other sectors decarbonize. These emissions have historically been difficult to regulate due to their international nature, falling outside the direct regulation of individual countries. This page examines the environmental impact of these industries, current regulatory efforts, emerging technologies, and future pathways toward reducing their carbon footprint in our climate-conscious world.

The Impact of Aviation Emissions

Aviation accounts for around 2.5% of global CO2 emissions, but its total climate impact is higher due to non-CO2 effects. When aircraft release emissions at high altitudes, including nitrogen oxides, water vapor, and particulates, they create contrails and cirrus clouds that contribute to additional warming effects. Some studies suggest that aviation's total contribution to anthropogenic climate forcing may be as high as 5% when these effects are considered.

Current Statistics

Global air passenger numbers have increased dramatically over the past decades, rising from approximately 1.6 billion in 2000 to over 4.5 billion by 2019 (before the pandemic). Despite improvements in fuel efficiency of approximately 1-2% per year, these gains have been outpaced by the overall growth in air travel demand, leading to rising absolute emissions from the sector.

Challenges for Decarbonization

Decarbonizing aviation presents unique challenges compared to other transport sectors. Batteries are currently too heavy for long-haul flights, limiting electrification to short-range aircraft. While sustainable aviation fuels (SAF) show promise, they currently cost 2-5 times more than conventional jet fuel and are in limited supply. The long development cycles for new aircraft (typically 10-15 years) also means that today's innovations will take considerable time to translate into fleet-wide emission reductions.

The Impact of Shipping Emissions

International shipping carries about 80% of global trade by volume and is responsible for approximately 2.89% of global CO2 emissions. If the shipping industry were a country, it would be the sixth largest emitter of greenhouse gases, ranking above Germany. The sector also emits significant amounts of sulfur oxides, nitrogen oxides, and particulate matter.

Current Emissions Trends

Shipping emissions have increased by approximately 30% since 1990, primarily due to the growth in global trade. While container ships have improved their efficiency by about 30% per container-kilometer over recent decades, these gains have been offset by increased demand for shipping services. Without significant technological changes or regulatory interventions, shipping emissions are projected to increase by up to 50% by 2050.

Challenges for Decarbonization

Maritime shipping faces substantial decarbonization challenges due to the energy density required for long ocean voyages, the long lifespan of vessels (typically 25-30 years), and the lack of developed alternative fuel infrastructure. Unlike road transport, where battery electric vehicles are gaining ground, battery technology is not yet viable for most ocean-going vessels due to weight and range constraints.

Regulatory Framework

Because aviation and shipping are international activities not contained within national borders, they have historically fallen outside the carbon reduction commitments (Nationally Determined Contributions) that countries make under the Paris Agreement. Instead, regulation has been addressed through specialized international bodies.

International Civil Aviation Organization (ICAO)

ICAO established the Carbon Offsetting and Reduction Scheme for International Aviation (CORSIA) in 2016. CORSIA aims to stabilize net emissions from international aviation at 2019 levels through 2035 by requiring airlines to purchase carbon offsets to cover any growth in emissions above a baseline. The scheme has been criticized by environmental groups for relying on offsets rather than direct emission reductions and for having voluntary participation in its early years.

International Maritime Organization (IMO)

The IMO adopted its Initial GHG Strategy in 2018, setting targets to reduce total greenhouse gas emissions from international shipping by at least 50% by 2050 compared to 2008 levels, and to reduce carbon intensity (emissions per transport work) by at least 40% by 2030. In 2023, the IMO revised these targets to reach net-zero emissions "by or around" 2050, aligning with the Paris Agreement's temperature goals.

Emerging Technologies and Solutions

Both industries are exploring multiple pathways to reduce their environmental impact, including technological innovations, operational improvements, and alternative fuels.

Aviation Solutions

• Sustainable Aviation Fuels (SAF): Made from biomass, waste oils, or synthetic processes, SAFs can reduce lifecycle carbon emissions by up to 80% compared to conventional jet fuel. Currently, SAF accounts for less than 0.1% of global jet fuel consumption.
• Hydrogen and Synthetic Fuels: Hydrogen propulsion systems and synthetic fuels (e-fuels) produced with renewable electricity offer potential long-term solutions for medium to long-haul flights.
• Hybrid and Electric Propulsion: Electric or hybrid-electric aircraft are being developed for short-haul routes, with several companies planning to launch smaller electric aircraft within the next decade.
• Airframe and Engine Efficiency: New aircraft designs, including blended wing bodies and open-rotor engines, could reduce fuel consumption by 20-30%.
• Operational Improvements: More efficient flight paths, continuous descent operations, and reduced taxiing times can provide immediate emissions reductions of 5-10%.

Shipping Solutions

• Alternative Fuels: The shipping industry is exploring multiple fuel options including ammonia, hydrogen, methanol, biofuels, and liquefied natural gas (LNG) as transitional fuels. Each presents different challenges regarding infrastructure, cost, and environmental trade-offs.
• Wind Propulsion: Modern wind-assisted propulsion technologies, including rigid wing sails, Flettner rotors, and kites, can reduce fuel consumption by 5-30% depending on the route and vessel.
• Hull Design and Efficiency: Advanced hull forms, air lubrication, and specialized coatings can reduce water resistance and improve fuel efficiency by 5-15%.
• Slow Steaming: Operating ships at reduced speeds can decrease fuel consumption and emissions by approximately 10-30% with modest increases in travel time.
• Digitalization: Optimal routing, weather forecasting, and just-in-time arrivals can improve operational efficiency.

Future Outlook

The decarbonization pathways for aviation and maritime shipping are complex and will require coordinated action across multiple fronts. The International Energy Agency's Net Zero by 2050 scenario estimates that aviation emissions need to fall by about 70% by 2050 compared to 2021 levels, while shipping needs to reduce emissions by nearly 80% by the same timeline.

Both sectors face substantial capital requirements for transition. The shipping industry alone may require $1-1.9 trillion in investments to achieve the IMO's 2050 targets, while aviation may need investments of similar magnitude to scale sustainable fuel production and develop new aircraft technologies.

Policy frameworks are evolving to provide stronger signals for investment. The European Union has included maritime transport emissions in its Emissions Trading System (ETS) since January 2024 and will include aviation departing from or arriving at EU airports. Carbon pricing mechanisms are likely to expand globally in the coming decade.

Conclusion

International aviation and shipping face significant but not insurmountable challenges in reducing their environmental impact. While both industries have taken initial steps toward addressing their emissions, accelerated efforts are needed to align with global climate goals. Success will depend on technological innovation, supportive policy frameworks, substantial financial investment, and global cooperation.

As consumers and businesses become increasingly aware of their carbon footprints, pressure will continue to mount on these sectors to demonstrate tangible progress. The coming decade will be critical in determining whether aviation and shipping can transition to sustainable models while continuing to provide the essential transportation functions that underpin modern global society and commerce.