While the GHG emissions from international maritime transport decreased by 13% between 2007 and 2012, they are projected to double in the period up to 2050. These are the main results of the Third IMO GHG Study, 2014
, which was adopted by the IMO in October 2014. CE Delft was a member of the consortium that carried out the study and was responsible for the emission projections.
The decrease in emissions in recent years can be attributed largely to vessels slowing down. Fleet activity during the period 2007-2012 demonstrates widespread adoption of slow steaming. The average reduction in at-sea speed relative to design speed was 12% and the average reduction in daily fuel consumption 27%, with many vessel type and size categories exceeding this average. In some oil tanker size categories, reductions in daily fuel consumption were approximately 50%, while certain container ship size categories reduced energy use by over 70%. Generally, smaller ship size categories operated without significant change over the period, as evidenced by more consistent fuel consumption and voyage speeds.
The future increase in emissions is attributable to a projected increase in activity, driven mainly by increased economic activity. Emissions are projected to increase despite regulatory and market-driven improvements in fleet efficiency. The new shipping emission projection scenarios are based on the Representative Concentration Pathways (RCPs) for future demand of coal and oil transport and Shared Socioeconomic Pathways (SSPs) for future economic growth, which have been developed by the Intergovernmental Panel on Climate Change (IPCC). SSPs have been combined with RCPs to develop four internally consistent scenarios of maritime transport demand. These are BAU scenarios, in the sense that they assume that current policies on the energy efficiency and emissions of ships remain in force, and that no increased stringencies or additional policies will be introduced. In line with common practice in climate research and assessment, there are multiple BAU scenarios to reflect the inherent uncertainties in projecting economic growth, demographics and the development of technology.