Exploring the scope for complementary sub-global policy to mitigate CO2 from shipping

For a high probability of avoiding dangerous interference with the climate system, all sectors must decarbonise over coming decades. Although shipping is an energy efficient transport mode, its emissions continue to grow. Compounding this, the sector's complexity, exclusion from emission inventories and slow progress towards a mitigation strategy, limit drivers towards meaningful change. Whilst there remains a preference within the industry for global mitigation policies, the urgency of required emission cuts necessitates exploration of complimentary sub-global measures. The debate surrounding such measures tends to focus on apportioning global shipping emissions to nations. To explore the policy implications of apportionment, the UK is used in this paper to illustrate how available apportionment regimes produce a wide range of emission estimates. Moreover, in the absence of transparent fuel consumption and freight data, they have limited sensitivity, rendering them currently obsolete for monitoring purposes. Nations, regions and organisations influence shipping, particularly in relation to operations, yet debate surrounding apportionment has arguably delayed consideration of sub-global polices and indicators. This paper makes a case for putting the apportionment debate aside in the short-term to open out the full span of options, consider influence over aspects of the shipping system, and how to monitor success.