New figures on global ship emissions

Container ships account for 26 per cent of the CO₂ emissions from international shipping.

In 2012 worldwide shipping consumed some 300 million tonnes of fuel oil, resulting in emissions of 949 million tonnes of carbon dioxide. Unless concerted action is taken, these emissions are expected to grow by up to five times by 2050.

Greenhouse gas emissions (GHG) from shipping activities around the world dropped by 14 per cent between 2007 and 2012, largely as a result of the economic crisis, according to a recent study for the International Maritime Organization (IMO).

The report says that shipping, in total, accounted for approximately 3.1 per cent of global carbon dioxide (CO₂) emissions and 2.8 per cent of total GHG emissions on a carbon dioxide equivalent (CO₂e) basis, on average for the six-year period 2007–2012.

Estimates of ships’ fuel consumption and emissions vary depending on the methodology used, and the study used both the top-down (bunker sales data) and the bottom-up (fleet activity data) methods for its estimates. According to the authors, the bottom-up approach provides the best estimates. Based on this main approach, the annual fuel consumption for all ships was approximately 300 million tonnes in 2012, resulting in CO₂ emissions of 949 tonnes, which equals 2.7 per cent of global CO₂ emissions for that year.

Average annual emissions of the air pollutants nitrogen oxides (NOx) and sulphur dioxide (SO₂) during the six-year time period 2007-2012 were estimated to amount to 20.9 and 11.3 tonnes, respectively, which represent about 15 and 13 per cent of global man-made emissions of these pollutants. (See Table 1.)

Table 1: Annual emissions from global shipping 2007-2012 (thousand tonnes).

Regarding fuel consumption for international shipping specifically (i.e. excluding domestic shipping and fishing vessels), the study cited sales in 2011 of 648.9 million tonnes according to the top-down estimate. Using the bottom-up approach resulted in fuel use of 849.5 million tonnes in that same year.

Heavy fuel oil dominates the fuel consumed by international shipping, with a share of approximately 85 per cent in 2012. Marine distillates accounted for nearly 15 per cent. 

According to the IMO’s global sulphur monitoring reports, the worldwide average fuel sulphur content in 2012 was 2.51 per cent for heavy fuel oil and 0.14 per cent for marine distillates.

Three types of ship dominate ship fuel consumption and consequently emissions. These are container ships, bulk carriers and oil tankers, which in 2012 were responsible for 26, 21 and 16 per cent respectively of the CO₂ emissions from international shipping.

According to the study, widespread reductions in ship speed took place during the 2007-2012 period, probably as a result of operators trying to cut costs. The average reduction of at-sea speed relative to design speed was 12 per cent, which led to a fall in average daily fuel consumption of 27 per cent. Some oil tanker size categories reduced daily fuel use by 50 per cent and some container ship size categories even reduced by more than 70 per cent. It was noted, however, that this does not translate into an equivalent percentage increase in efficiency, because a greater number of ships (or more days at sea) are required to do the same amount of freight work.

It is expected that global demand for shipping will keep growing over the next few decades, resulting in a projected rise in fuel use and CO₂ emissions of between 50 and 250 per cent under a business-as-usual scenario. Additional action to improve efficiency and reduce emissions can limit the growth in emissions, but it was noted that even modelled improvements with the greatest energy savings could not yield a downward trend.

In total, the study modelled 16 scenarios with different economic conditions, levels of fuel use and air pollution controls, and with and without further efficiency rules.

The scenario analysis starts with four different scenarios of transport demand (disaggregated into cargo groups). For each of these there is one ECA/fuel mix scenario that keeps the share of fuel used in Emission Control Areas (ECA) constant over time and has a slow penetration of liquefied natural gas (LNG) in the fuel mix, and another that projects a doubling of the amount of fuel used in ECAs and has a higher share of LNG in the fuel mix.

Then, for each of the eight combinations of demand and ECA scenarios, there are two efficiency trajectories, one assuming an ongoing effort to increase the fuel-efficiency of new and existing ships after 2030, resulting in a 60 per cent improvement over the 2012 fleet average by 2050, and the other assuming a 40 per cent improvement by 2050.

According to the scenario analysis, emissions of nitrous oxide (N₂O), volatile organic compounds (NMVOC) and carbon monoxide (CO) will rise roughly in line with those of CO₂, while a greater increase is projected for methane (CH₄) as more ships switch to LNG. (See Table 2.)

Table 2: Summary of scenarios for future (2020 and 2050) emissions from international shipping. Figures show the median change relative to 2012, with the minimum and maximum changes shown in parenthesis.

Emissions of NOx and particulate matter (PM) are also expected to continue to increase, but at a slightly slower rate compared to CO₂. The only pollutant showing a downward trend is SO₂ – reductions that will result from implementing the strengthened sulphur standards adopted by the IMO in 2008.

The report will be presented to the 67th meeting of the IMO’s Marine Environment Protection Committee (MEPC 67) to be held in London in mid-October, where it is intended to feed in to the discussions about how to best address GHG emissions from the shipping sector.

Christer Ågren

The report: Third IMO GHG Study 2014. International Maritime Organization (IMO) MEPC 67/INF.3, 25 July 2014.