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| Fig. 1: Total shipping emissions by class 2015 (million tonnes CO2). [4] (Source: A. Mensah). |
The transportation industry accounts for about 27.3% of US greenhouse gas emissions. Of this 27.3 road transport accounts for the most at 23%, than air at 2.4%, and lastly shipping, rail, and other at about 1.9%. [1] However, 90% of the goods in the world are transported by the maritime shipping sector. [2] Therefore, I am interested in the total energy per year used by the maritime shipping sector. The different types of essential goods that are transported by the maritime shipping sector are reflected in the different types of transport ships types. These include oil tankers, bulk carriers, combination carriers, general cargo ships, container ships, liquified petroleum gas carriers, natural gas carriers, chemical parcel tankers, specialized tankers, reefers, offshore supply vessels, and other goods. [2] Considering the largest categories by tons loaded per year, tanker trade, main bulk, container, and other dry cargo, we will be able to estimate the yearly energy use through some calculations and simplifying assumptions.
In 2021, the world had 99,800 ships with a capacity of 100 gross tons and above. This resulted in 2.13 × 109 deadweight tonnes of capacity. [2] Sea trade was about 10.7 billion tons with 815.6 million twenty-foot equivalent units (TEUs) of capacity traded. Of the world maritime trade in 2021, Asia accounts for 54%, the Americas 18%, Europe 15%, Oceania 8%, and Africa 6%. [2] In the shipping sector, large and very large ships (those that constitute the 99,800 ships) are responsible for about 85% of net greenhouse gas emissions. [3]
The primary way that energy is consumed by the maritime sector is through the use of fossil fuels as power for vessels. The 2018 fuel mix for international shipping comprised 79% heavy fuel oil (HFO), 16% marine diesel oil (MDO), 4% liquefied natural gas (LNG), and less than 0.1% methanol. In terms of energy efficiency, data shows that during low oil price periods, the shipping sector pays less attention to its energy usage. Conversely, the sector adapts during periods of high oil prices, increasing its activity while using energy resources more efficiently. [3]
According to Comer et al., the total CO2 emissions in 2015 were at 7.70 × 108 tonnes. [4] As seen in Fig. 1, container shipping was the highest of all shipping classes in 2015 emissions.
If we consider the amount in TEU of cargo transported in 2015, 171 million, we can calculate the CO2 emissions per container. [2] Of all the moving transport, 25.2% 25.18795479% is due to cargo shipping in a cellular format. [4] Therefore in 2015, we have:
| Total CO2 Emissions From Cellular Shipping | = | 7.70 × 108 tonnes × 0.252 |
| = | 1.94 × 106 tonnes |
Now we divide by the number of containers to get the carbon cost per container:
| Total CO2 Emissions Per Container | = | 1.94 × 108 tonnes 1.71 × 108 containers |
|
| = | 1.13 tonnes container-1 | ||
| = | 1130 kg container-1 |
Thus in 2015 the Emissions Per Container were 1130 kg container-1.
Overall we see that the average emissions per container are at 1130 kg and as seen in Fig. 1 container shipping is the highest of all shipping classes in 2015 emissions. According to IRENA forecasts, maritime trade could increase by between 40% and 115% by 2050 compared to 2018 levels. [3] Around 99% of the energy demand from the international shipping sector is met by fossil fuels, with fuel oil and marine gas oil making up as much as 95% of the total demand. IRENA has warned that without suitable mitigation policies, GHG emissions associated with the shipping sector could rise by between 50% and 250% by 2050. The broad range of potential outcomes presented by IRENA highlights the uncertainty in how the sector will develop over the next 30 years, but even the lower end of the range would jeopardize efforts to limit global warming. To reduce this uncertainty, it is essential to plan ahead and analyze pathways to decarbonize the international shipping sector by 2050. According to the IRENA, in the short term, this can be done through the advancement of biofuels, whereas in the long term, hydrogen-based fuels will drive the decarbonization of the sector.
© Anthony Mensah. The author warrants that the work is the author's own and that Stanford University provided no input other than typesetting and referencing guidelines. The author grants permission to copy, distribute and display this work in unaltered form, with attribution to the author, for noncommercial purposes only. All other rights, including commercial rights, are reserved to the author.
[1] "Carbon Footprint Factsheet, " Center for Sustainable Systems, University of Michigan, Pub. No. CSS09-05, September 2022.
[2] "Review of Maritime Transport," United Nations, 2015, 2019, 2021.
[3] "A Pathway to Decarbonize the Shipping Sector by 2050," International Renewable Energy Agency, 2020.
[4] B. Comer et al., "Black Carbon Emissions and Fuel Use in Global Shipping, 2015," International Council on Clean Transportation, May 2017.