Engine emissions have been regulated by the IMO under MARPOL Annex VI since 2005 when the 1997 Protocol adding the annex came into effect.

In the initial wording of Annex VI there was no mention whatsoever of greenhouse gases (GHGs) and it would be another six years before the IMO adopted the efficiency measures such as EEDI and ship energy efficiency management plans (SEEMP) which aimed at reducing CO2 emissions.

The first actions on GHGs was limited to reductions in CO2 and did not occur until 2015 when Phase 1 of EEDI became effective for ships over 400GT.