International shipping accounts for around 2.2% of global carbon dioxide(CO2)emissions(Smith et al.,2014).Emissions from international shipping are expected to increase by 50%-250% by 2050,mainly due to the growth of the world maritime trade(Smith et al.,2014).However,efforts to control CO2 emissions from the global shipping industry are absent from the Kyoto Protocol and Paris Agreement.Therefore,the International Maritime Organi-zation(IMO)has released an ambitious strategy to cut the total annual greenhouse gas emissions of shipping by at least 50% by 2050,compared with 2008(IMO,2018).