Shipping transition under green energy supply risks: three-dimensional mechanism analysis

With the gradual implementation of shipping carbon dioxide tax policies, green energy transition has become essential for low-carbon coordination in the port–shipping supply chain. This study develops a ‘1v2’ port–shipping supply chain game model incorporating carbon taxation, green energy supply uncertainty and market competition intensity. The model comprises one oligopolistic port and two perfectly competitive shipping companies, examining green investment decisions from integrated policy, resource and market perspectives. Results demonstrate that a stable green energy supply significantly enhances shipping companies’ transition incentives, whereas intensified market competition induces conservative behaviours and suppresses collaborative green investment. An appropriately designed carbon dioxide tax level can restore green investment incentives and alleviate transition constraints. Further analysis reveals that shipping companies’ heterogeneity amplifies competition, thereby reducing social welfare when all shipping companies undertake green transition. Moderate adjustment of the carbon dioxide tax interval shifts equilibrium from asymmetric to symmetric green transition, enabling a ‘triple-win’ outcome. Moreover, a port–shipping collaborative green investment mechanism eliminates asymmetric equilibria and enlarges the equilibrium region of symmetric green transition. Overall, this study provides theoretical support for maritime carbon dioxide tax policy design and a decision-making framework for coordinated emission reduction and sustainable development in port–shipping supply chains.