White paper

Reducing GHG Emissions from Ships

Marginal abatement cost (MAC) curves are a staple of policy discussions where there is a need to illustrate the incremental contributions of parts to a whole. As this paper demonstrates, they provide a simple and elegant way to illustrate greenhouse gas (GHG) emission reductions from design standards, retrofit technologies, and operational measures that improve ship energy efficiency relative to their costs.

The first generation of MAC curves for marine GHG reductions effectively stimulated discussions about measures and standards, but lacked detail. Development of more tailored policies for the industry requires MAC values with greater resolution, so that they are more applicable to specific ship types in the context of future trends. Such policies are critical to creating appropriate incentives and market signals in a diverse and competitive industry. Policies based on more general, low-resolution data are more likely to lead to unintended inequities and poorly matched incentives.

To improve the precision of marine MAC values, and specifically to support policies in development at the International Maritime Organization (IMO), the ICCT and its partners worked with the Society of Naval Architects and Marine Engineers (SNAME) to identify 50 potential ship efficiency measures. Of these, 22 had sufficient performance data available to calculate their associated aggregated cost effectiveness and reduction potential. The study examined these measures against 53 ship types and sizes over 30 years. The marginal costs of this subset of measures were averaged to produce a much more refined illustration of how by 2020 the industry’s growing fleet could reduce annual CO2 emissions by 436 million metric tons (mmt), or 33% of the projected annual total. Of that amount, 340 mmt (26% of the total) could be achieved for a net negative cost after fuel and other savings are accounted for.

This paper summarizes work originally submitted to the IMO in a detailed technical report, available here.