|Transport-related annual emissions of CO2, NOx, SO2 and PM10 and the fuel consumption in Tg estimated for the year 2000 (rescaled from Eyring et al., J. Geophys. Res., 2005a). Click to enlarge.|
Current carbon dioxide emissions from the shipping industry likely exceeds those from aviation, and could double by 2050, according to recent studies by the Institut für Physik der Atmosphäre (IPA) of the Deutsches Zentrum für Luft- und Raumfahrt (DLR) and by the College of Marine and Earth Studies of the University of Delaware.
In addition, marine emissions of SO2 could also double, while NOx emissions could exceed those of road traffic in the same time span.
The studies 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 Tg = 1012 g = 1 million metric tons = 1 Mt). The same studies put aviation emissions of CO2at about 650 Tg.
Given uncertainties in all emission inventories, these figures should be considered best estimates within a bounded range of 600 to 900 Tg of CO2 per year, according to the IPA. The IPA 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 (NOx) emissions and for around 8% of sulfur dioxide (SO2) emissions. The relatively high contribution is a result of marine engines operating at high temperatures and pressures without effective NOx emission reduction technologies and because of the 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.
Future scenarios demonstrate that significant reductions are needed to offset increased emissions due to growth in seaborne trade and cargo energy intensity. If no aggressive emission reduction strategies are introduced, CO2 and SO2 emissions from ships could double present-day values by 2050, and NOx emissions could exceed present-day global road transport.
An International Maritime Organization (IMO) study of greenhouse gas emissions estimates that emissions from the global fleet would increase dramatically in the next 20 years as globalization leads to increased demand for bigger, faster ships, according to a report in the Guardian. Without action the IMO predicts that by 2020, emissions from ships would increase up to 72%.
Global comparisons of emission totals from different transport modes describe only part of the picture, IPA cautions. 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.