Sea fairer: Maritime transport and CO2 emissions

OECD Observer

A clean launch ©Reuters/Nikola Solic

International shipping emits as much CO2 as some of the world's largest countries. What can be done?

Some 90% of world trade in tonnes is carried by ship, and containers represent 70% of total maritime trade by value. Per kilometre, shipping is one of the lowest emitting freight transport options around; at 10-15 grammes per tonne-kilometre, it is lower than rail (19-41g/tkm), trucking (51-91g/tkm) and aviation (673-867g/tkm). But the carbon footprint of the sector as a whole is as large as some major countries.

International maritime activity accounted for 543 Mt of CO2 emissions from fuel combustion in 2005, according to data from the International Energy Agency (IEA), a sister organisation of the OECD and the International Transport Forum. The figure is calculated by the sale of fuel to vessels whose next port-of-call is outside the country, and it places CO2 emissions from international maritime transport in 8th place in the world between Canada and the UK.

The International Maritime Organization, however, has recently updated its own estimate using a detailed bottom-up fleet inventory and has found that international maritime activity emitted a total of 1,120 Mt of CO2–more than twice the IEA estimate for 2005.

This new estimate places international maritime emissions in 6th place in the world between India and Germany and nearly three times that of international aviation. The bulk of shipping’s emissions stem from cargo vessels, with passenger ships representing only 3% of total ship CO2 emissions, a share which is declining.

Total maritime trade has doubled from 1985 to 2007; total containerised trade has grown eight-fold over the same period and currently represents 16% of all maritime trade by weight (and a much larger share by value). Depending on the weight carried per container unit, trade in containers measured by deliveries is projected to more or less triple from 2000 to 2020.

In terms of container movements including transhipments, Drewry Shipping Consultants forecasts a more than six-fold rise from 2000 to 2020. This growth has important GHG repercussions as the average installed power on container vessels is higher than on most other types of vessels and, given the speeds at which container vessels travel, increased container vessel activity will result in greater maritime CO2 emissions than might otherwise have been expected based on past fleet structure. Nonetheless, in aggregate, energy use per tonne delivered by sea has generally followed a decreasing trend from 1985 to 2007 with the advent of more efficient engines, better propellers and larger vessels.

The potential for new technology penetration within the world ship fleet is limited by the long life-span of vessels–up to 30-40 years. Many vessels built today incorporate energy-saving technologies. But as with cars, in many cases, much of these energy savings have been used to buy more power and speed, not to reduce energy use.

This is particularly evident in the fast-growing containership market where new vessels are being built to carry upwards of 10,000 containers and sail at 25 knots, compared with speeds of 21-23 knots in the 1990s. Because a ship must overcome water resistance, changes in energy use and CO2 emissions are particularly sensitive to ship speed–a 4% increase in ship speed entails about a 13% increase in CO2 emissions.

Better hull and propeller design and incremental engine technology improvements can contribute up to 30% energy efficiency improvements for new builds. Future propulsion options based on fuel cells may also be feasible in two or three vessel generations. Advanced sail technology is already being trialled and may also play a limited role in the future.

However, much of the energy saving potential for maritime transport comes through operational changes to the existing fleet which could deliver up to 20% fuel savings. The foremost option is reducing speed. However, this raises operational challenges, especially for container vessels that run on set routes and schedules. Providing the same level of service at slower speeds might require adding vessels to the route, thus eroding some of the fuel savings, or increase costs to owners as vessels arrive at night or on the weekend when stevedoring costs are higher.

Other sources of energy-saving improvements for existing vessels entail shifting in-port power to shore-based auxiliary power units rather than ship engines. Improvements in on-board auxiliary power generation can also be a source of non-negligible fuel savings.



See International Maritime Organization’s website at

See Drewry Shipping Consultants,

For more on International Transport Forum’s work on maritime shipping, contact

©OECD Observer No 267, May-June 2008

Economic data

GDP growth: +0.6% Q1 2019 year-on-year
Consumer price inflation: 2.3% May 2019 annual
Trade: +0.4% exp, -1.2% imp, Q1 2019
Unemployment: 5.2% July 2019
Last update: 8 July 2019

OECD Observer Newsletter

Stay up-to-date with the latest news from the OECD by signing up for our e-newsletter :

Twitter feed

Subscribe now

<b>Subscribe now!</b>

To order your own paper editions,email

Online edition
Previous editions

Don't miss

  • MCM logo
  • The following communiqué and Chair’s statement were issued at the close of the OECD Council Meeting at Ministerial level, this year presided by the Slovak Republic.
  • Food production will suffer some of the most immediate and brutal effects of climate change, with some regions of the world suffering far more than others. Only through unhindered global trade can we ensure that high-quality, nutritious food reaches those who need it most, Angel Gurría, Secretary-General of the OECD, and José Graziano da Silva, Director-General of the United Nations Food and Agriculture Organization, write in their latest Project Syndicate article. Read the article here.
  • Globalisation will continue and get stronger, and how to harness it is the great challenge, says OECD Secretary-General Gurría on Bloomberg TV. Watch the interview here.
  • OECD Secretary-General Angel Gurría with UN Secretary-General António Guterres at the 73rd Session of the UN General Assembly, in New York City.
  • The new OECD Observer Crossword, with Myles Mellor. Try it online!
  • Listen to the "Robots are coming for our jobs" episode of The Guardian's "Chips with Everything podcast", in which The Guardian’s economics editor, Larry Elliott, and Jeremy Wyatt, a professor of robotics and artificial intelligence at the University of Birmingham, and Jordan Erica Webber, freelance journalist, discuss the findings of the new OECD report "Automation, skills use and training". Listen here.
  • Do we really know the difference between right and wrong? Alison Taylor of BSR and Susan Hawley of Corruption Watch tell us why it matters to play by the rules. Watch the recording of our Facebook live interview here.
  • Has public decision-making been hijacked by a privileged few? Watch the recording of our Facebook live interview with Stav Shaffir, MK (Zionist Union) Chair of the Knesset Committee on Transparency here.
  • Can a nudge help us make more ethical decisions? Watch the recording of our Facebook live interview with Saugatto Datta, managing director at ideas42 here.
  • The fight against tax evasion is gaining further momentum as Barbados, Côte d’Ivoire, Jamaica, Malaysia, Panama and Tunisia signed the BEPS Multilateral Convention on 24 January, bringing the total number of signatories to 78. The Convention strengthens existing tax treaties and reduces opportunities for tax avoidance by multinational enterprises.
  • Globalisation’s many benefits have been unequally shared, and public policy has struggled to keep up with a rapidly-shifting world. The OECD is working alongside governments and international organisations to help improve and harness the gains while tackling the root causes of inequality, and ensuring a level playing field globally. Please watch.
  • Checking out the job situation with the OECD scoreboard of labour market performances: do you want to know how your country compares with neighbours and competitors on income levels or employment?
  • Trade is an important point of focus in today’s international economy. This video presents facts and statistics from OECD’s most recent publications on this topic.
  • The OECD Gender Initiative examines existing barriers to gender equality in education, employment, and entrepreneurship. The gender portal monitors the progress made by governments to promote gender equality in both OECD and non-OECD countries and provides good practices based on analytical tools and reliable data.
  • Interested in a career in Paris at the OECD? The OECD is a major international organisation, with a mission to build better policies for better lives. With our hub based in one of the world's global cities and offices across continents, find out more at .
  • Visit the OECD Gender Data Portal. Selected indicators shedding light on gender inequalities in education, employment and entrepreneurship.

Most Popular Articles

OECD Insights Blog

NOTE: All signed articles in the OECD Observer express the opinions of the authors
and do not necessarily represent the official views of OECD member countries.

All rights reserved. OECD 2019