Prof. Dr. James J. Corbett
College of Marine and Earth Studies
University of Delaware
Newark, USA
Phone: +1-302-831-0768
E-Mail: James J Corbett
http://www.ocean.udel.edu/cms/jcorbett/

Figure 1: Transport-related annual emissions of CO2, NOx, SO2 and PM10 and the fuel consumption in Tg (1 Tg = 10^12 g = Mt) estimated for the year 2000. Modified from Figure 3 of  Eyring et al. (2005), Emissions from international shipping: 1. The last 50 years, J. Geophys. Res., 110, D17305, doi:10.1029/2004JD005619 (Copyright 2005 by the American Geophysical Union).

Regulating transport emissions requires comprehensive knowledge of the present day fuel consumption and emissions, their potential future evolutions, and mitigation options. Recent studies by the Institute of Atmospheric Physics of the German Aerospace Center DLR and by the College of Marine and Earth Studies of the University of Delaware in the United States of America (USA) reveal converging estimates of current ship emissions and suggest that shipping emitted around 800 Tg CO₂ and contributed around 2.7% to all anthropogenic CO₂ emissions in 2000 [1,2] (1 Tg = 10¹² g = 1 million metric tons = 1 Mt). Given uncertainties in all emission inventories, these figures should be considered our best estimates within a bounded range of 600 to 900 Tg of CO₂ per year [2]. Our research concludes that CO₂ emissions from shipping are of the same order as published CO₂ estimates for aviation.

For comparison, aviation and road transport contributed around 2.2% and 14%, respectively. Other comparisons suggest that shipping accounts for around 15% of all global anthropogenic nitrogen oxides (NO_x) emissions and for around 8% of sulfur dioxide (SO₂) emissions [1,2]. The relatively high contribution results because most marine engines operate at high temperatures and pressures without effective NO_x emission reduction technologies and because of high average sulfur content (2.4%-2.7%) in marine fuels.  

Recent studies from DLR have shown that fuel consumption from ocean-going ships has increased by a factor of 4.3 from 1950 to 2000, reaching around 280 Tg today [1]. And importantly, future scenarios demonstrate that significant reductions are needed to offset increased emissions due to growth in seaborne trade and cargo energy intensity [3]. If no aggressive emission reduction strategies are introduced, CO₂ and SO₂ emissions from ships could double present-day values by 2050, and NO_x emissions could exceed present-day global road transport.

Global comparisons of emission totals from different transport modes describe however only part of the picture. For example, the related passenger and freight transported volumes will need to be considered in addition. Also, the distribution of shipping activity follows major trade routes, such that ship emissions near coastal areas affect regional air quality, environment, and public health. Evaluating these impacts requires atmospheric research that helps developing appropriate reduction strategies and allows the industry to incorporate, with greater confidence, environmental considerations into their operations. Our inventories and further planned research contribute to that ongoing science-technology-policy dialogue.   

References:

[1] Eyring, V., H.W. Köhler, J. van Aardenne, and A. Lauer (2005a), Emissions from international shipping: 1. The last 50 years, J. Geophys. Res., 110, D17305, doi:10.1029/2004JD005619.

[2] Corbett, J.J., and H.W. Köhler (2003), Updated emissions from ocean shipping, J. Geophys. Res., 108, doi:10.1029/2003JD003751.

[3] Eyring, V., H. W. Köhler, A. Lauer, and B. Lemper (2005b), Emissions from international shipping: 2. Impact of future technologies on scenarios until 2050, J. Geophys. Res., 110, D17306, doi:10.1029/2004JD005620.

Other Press Information:

• Reconciling past and future trends in ship work, energy, and emissions, more...
• Eyring, V., J. J. Corbett, D. S. Lee, J. J. Winebrake,  Brief summary of the impact of ship emissions on atmospheric composition, climate, and human health; Health and Environment Sub-Group of the International Maritime Organization: London, UK, 6 November 2007.
• Aerosols from ocean shipping cause a significant negative climate forcings, more...