Greenhouse gas emissions from global shipping, 2013–2015

Published: 2017.10.17

Naya Olmer, Bryan Comer, Biswajoy Roy, Xiaoli Mao, and Dan Rutherford

Reducing greenhouse gas (GHG) emissions is the key to avoiding the most catastrophic impacts of climate change. Despite international shipping being excluded from the Paris Agreement, the International Maritime Organization (IMO) is developing its own strategy to reduce GHGs from ships. IMO member states will need to understand recent trends in ship activity and emissions to develop an effective strategy. Policymakers would benefit from the most recent understanding of the drivers of shipping emissions (e.g., transport demand, ship capacity, and speed), in order to make informed decisions. By considering this information, IMO is more likely to reduce GHG emissions from international shipping in a targeted and cost-effective way.

In this report, we describe trends in global ship activity and emissions for the years 2013 to 2015. We found that emissions generally increased over this period, with efficiency improvements more than offset by increases in activity. Key findings include:

  • Fuel consumption is increasing. Total shipping fuel consumption increased from 291 to 298 million tonnes (+2.4%) from 2013 to 2015.
  • Shipping GHG emissions are increasing despite improvements in operational efficiency for many ship classes. Increasing emissions are being driven by rising demand for shipping and the associated consumption of fossil fuels.
  • Black carbon is a major contributor to shipping’s climate impacts. After CO2, black carbon (BC) contributes the most to the climate impact of shipping, representing 7% of total shipping CO2-eq emissions on a 100-year timescale and 21% of CO2-eq emissions on a 20-year time scale.
  • Increases in efficiency have not reduced absolute CO2 emissions from ships. Although the CO2 intensity of many major ship classes decreased (i.e., they became more efficient) from 2013 to 2015, total CO2 emissions from ships increased. Thus, increases in distance travelled due to a greater demand for shipping more than offset gains in operational efficiency during the period studied.
  • The biggest ships are speeding up and emitting more. Whereas average ship cruising speeds remained largely unchanged between 2013 and 2015, the largest oil tankers (>200,000 dwt) and the largest container ships (>14,500 TEU) sped up and emitted more in 2015 compared with 2013. In fact, the largest oil tankers increased their cruising speed over ground (SOG) by nearly 4%, and the largest container ships increased their cruising SOG more than 11%. If more ships follow suit and speed up, the CO2 efficiency of the maritime transport sector will degrade.
  • Absolute reductions in ship emissions will require concerted action to improve the energy efficiency of shipping and to develop and deploy alternative fuel and propulsion concepts. The only way to reduce emissions from ships without constraining demand is to substantially reduce the amount of CO2 and CO2-equvalent emitted per unit of transport supply.

An in-depth review of the methodology used in this report is included as a separate document titled “detailed methodology" under the attachments section at the bottom of the page. Additionally, we provide data describing ship activity and emissions by ship class; ship class and capacity bin; and flag state in the "supplemental material" Excel sheet below.

PDF icon Detailed methodology1.26 MB
File Supplemental material (.xls)360.16 KB