Fourth Greenhouse Gas Study 2020

Highlights and Executive Summary of the Fourth IMO GHG Study 2020


Emissions inventory

– The greenhouse gas (GHG) emissions — including carbon dioxide (CO2), methane (CH4) and nitrous oxide (N2O), expressed in CO2e — of total shipping (international, domestic and fishing) have increased from 977 million tonnes in 2012 to 1,076 million tonnes in 2018 (9.6% increase). In 2012, 962 million tonnes were CO2 emissions, while in 2018 this amount grew 9.3% to 1,056 million tonnes of CO2 emissions

– The share of shipping emissions in global anthropogenic emissions has increased from 2.76% in 2012 to 2.89% in 2018.

– Under a new voyage-based allocation of international shipping, CO2 emissions have also increased over this same period from 701 million tonnes in 2012 to 740 million tonnes in 2018 (5.6% increase), but to a lower growth rate than total shipping emissions, and represent an approximately constant share of global CO2 emissions over this period (approximately 2%), as shown in Table 1. Using the vessel-based allocation of international shipping taken from the Third IMO GHG Study, CO2 emissions have increased over the period from 848 million tonnes in 2012 to 919 million tonnes in 2018 (8.4% increase).

– Due to developments in data and inventory methods, this study is the first IMO GHG Study able to produce greenhouse gas inventories that distinguish domestic shipping from international emissions on a voyage basis in a way which, according to the consortium, is exactly consistent with the IPCC guidelines and definitions.1

– Projecting the same method to 2008 emissions, this study estimates that 2008 international shipping GHG emissions (in CO2e) were 794 million tonnes (employing the method used in the Third IMO GHG Study, the emissions were 940 million tonnes CO2e).

Carbon intensity 2008, 2012 – 2018

– Carbon intensity has improved between 2012 and 2018 for international shipping as a whole, as well as for most ship types. The overall carbon intensity, as an average across international shipping, was 21 and 29% better than in 2008, measured in AER and EEOI respectively in the voyage-based allocation; while it was 22 respectively 32% better in the vessel-based allocation (Table 2). Improvements in carbon intensity of international shipping have not followed a linear pathway and more than half have been achieved before 2012. The pace of carbon intensity reduction has slowed since 2015, with average annual percentage changes ranging from 1 to 2%.

– Annual carbon intensity performance of individual ships fluctuated over years. The upper and lower quartiles of fluctuation rates in EEOI of oil tankers, bulk carriers and container ships were around ±20%, ±15% and ±10% respectively. Quartiles of fluctuation rates in other metrics were relatively modest, yet still generally reaching beyond ±5%. Due to certain static assumptions on weather and hull fouling conditions, as well as the non-timely updated AIS entries on draught, actual fluctuations were possibly more scattered than estimated, especially for container ships. 

Emission projections 2018 – 2050

– Emissions are projected to increase from about 90% of 2008 emissions in 2018 to 90-130% of 2008 emissions by 2050 for a range of plausible long-term economic and energy scenarios (Figure 1).

– Emissions could be higher (lower) than projected when economic growth rates are higher (lower) than assumed here or when the reduction in GHG emissions from land-based sectors is less (more) than would be required to limit the global temperature increase to well below 2 degrees centigrade.

– Although it is too early to assess the impact of COVID-19 on emission projections quantitatively, it is clear that emissions in 2020 and 2021 will be significantly lower. Depending on the recovery trajectory, emissions over the next decades maybe a few percent lower than projected, at most. In all, the impact of COVID-19 is likely to be smaller than the uncertainty range of the presented scenarios.

1 The choice of the method to distinguish domestic shipping emissions from international shipping emissions does not interpret existing IMO instruments, nor prejudge any future policy developments at IMO and would not constitute IMO's views on the interpretation of the 2006 IPCC Guidelines on national greenhouse gas inventories.