| Recent attention on ship emissions has produced a several independent estimates of ship fuel use and emissions that appear different. However, these estimates are often for different base-years, and most activity-based estimates show good agreement with each other when adjusted for freight growth. Based on our published estimates and using freight growth trends, we estimate that current-year (2007) fuel used by ships is between 370 and 410 million metric tons. This update provides some background that may be useful.
 Figure
1: World fleet fuel consumption and international marine bunker fuel statistics in million ton of oil equivalents (Mt) from different estimates (Corbett and Köhler, 2003; Eyring et al., 2005; and Gunner, 2007). Symbols indicate point estimates, while the lines show back- and forecasts calculated assuming proportionality with change in freight ton-miles. |
To achieve same-year estimates, the growth rates must be considered and chosen to be consistent with energy required to move increased goods. Work done in global trade is generally proportional to the energy required; this leads to a well understood correspondence between fuel use and seaborne trade in tonne-miles. Recent annual growth rates in total seaborne trade in ton miles have been 5.2% on average from 2002 to 2007, a lot higher than in past decades (UNCTAD 2007; see also Figure 1). Accordingly, fuel consumption has increased significantly as the total installed power increased.
Total ship fuel use is not reflected in data for international fuel sales reported by IEA because the allocation of fuel sales is not made according to vessel fuel consumption but according to agreements about designating a sale as internatioanl or domestic. As fleet logistics have increased the number of multiple in-country port calls (primarily through containerized logistics), the degree of potential error has increased between international fuel sales and total fuel consumption.
Figure 1 shows the fuel consumption from 1950 to 2007 as reported in the literature in addition to the back- and forecast calculated from the time evolution of freight ton-miles. As shown, the various independent activity-based estimates simply show that fuel consumption has continued to increase since the base-year(s) represented in our earlier work. We consider this to be substantial agreement with and confirmation of our earlier estimates. This is also consistent with increased containerization over these decades.
Our review of the data for historic trends and forecasts suggests that the lowest growth rate that has been supported by recent detailed analysis is ~3.6% (EnSys Energy & Systems Inc. and Navigistics Consulting, API, 2007); our studies report studies and evidence supporting energy growth rates similar to annual freight growth averaging 4.1% per year or higher (Corbett and Wang, ARB, 2007; Corbett and Winebrake, FOEI, 2007).
Some shipping growth rates are much higher. Cargo moved by the container trade, measured in cargo tons, grew in 2006 by 11.2 %, reaching 1.13 billion tons. Over the last two decades, global container trade (in tons) is estimated to have increased at an average annual rate of 9.8%, while the share of containerized cargo in the world’s total dry cargo is estimated to have increased from 7.4% in 1985 to 24% in 2006. In this context, it is important to note that over 70 % of the value of world international seaborne trade is being moved in containers. Given the shift to higher-speed containerized shipping, it is only with substantial increases in cargo-energy efficiency that these freight growth rates in containerized cargoes result in an energy-demand growth rate as small as ~4% per year.
Our published research studies over the past ten years showed where ship emissions occur, identified which land regions are impacted, and quantified environmental and human health impacts. These impacts will increase along with trade growth unless shippers and policymakers institute currently available, cost-effective, and feasible technology-policy strategies. Others independently report results within our ranges, confirming what many in industry have come to accept: Ships need to reduce emissions, and ships can better decouple CO2 and energy from goods movement. We remain focused on a future of freight sustainability that includes ships, planes, trucks and trains.
References:
[1] Corbett, J.J., and H.W. Köhler (2003), Updated emissions from ocean shipping, J. Geophys. Res., 108, doi:10.1029/2003JD003751.
[2] Eyring, V., H.W. Köhler, J. van Aardenne, and A. Lauer (2005), Emissions from international shipping: 1. The last 50 years, J. Geophys. Res., 110, D17305, doi:10.1029/2004JD005619.
[3] International Energy Agency (IEA) (2006), CO2 Emissions from Fuel Combustion (1971-2004), International Energy Agency, Paris, France
[4] Estimates reported by Dr. Tim Gunner in Shipping, CO2 and other Air Emissions at the Technical workshop meeting on emissions from aviation and maritime transport, Oslo, October 2007. http://www.eionet.europa.eu/training/bunkerfuelemissions
[5] United Nations Conference on Trade and Development (UNCTAD) 2007, Review of Maritime Transport 2007, United Nations: Geneva. p. 167.
[6] EnSys Energy & Systems Inc., and Navigistics Consulting (2007), Analysis of Impacts on Global Refining & CO2 Emissions of Potential MARPOL Regulations for International Marine Bunker Fuels, Final Report, American Petroleum Institute, Lexington, MA.
[7] Corbett, J. J., C. Wang, J. Firestone. (2007), Estimation, Validation, And Forecasts Of Regional Commercial Marine Vessel Inventories, Final Report, State of California Air Resources Board and the California Environmental Protection Agency and the Commission for Environmental Cooperation of North America, Sacramento, CA.
[8] Corbett, J. J., C. Wang, J.J. Winebrake, E. Green. (2007), Allocation and Forecasting of Global Ship Emissions, 26 pp, Clean Air Task Force and Friends of the Earth International, Boston, MA.
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