IMERS uses a novel hybrid economic instrument that we call cap-and-levy
(it was presented by Norway and others as a hybrid scheme, and was also called cap-and-charge; some people use the name charge-cap-and-trade to signify the trading aspect of the instrument).
A levy (emission charge) is established in such a way that an agreed emission target (cap) will be delivered for international shipping by purchasing emission credits if required.
Cap-and-levy is an example of GHG policy that has the highest theoretical cost-effectiveness. The different GHG policy options are shown below, ordered from the highest to the lowest cost effectiveness.