This review comprehensively and systematically examines the research on the mechanisms of carbon emissions in maritime transportation at both micro and macro levels, summarizing three major micro factors and three major macro factors, along with seven interrelated effects. Micro factors directly affect ships, including ship technology factors, fleet operation factors, and shipping physical factors. Macro factors affect micro parts through market regulation, and indirectly affect shipping carbon emissions, including international governance factors, trade factors, and disaster factors. Interactions between different factors and between factors and carbon emissions occur through scale effects, structure effects, technology effects, cost-saving effects, interruption effects, energy intensity effects, and activity intensity effects. Challenges in current maritime carbon reduction arise from the development and popularization of ship technology, the establishment of ship planning platforms, and the formulation of scientific and rational environmental tax policies. Future efforts should focus on further quantifying the specific impacts of ocean shipping on geopolitics and natural disasters, with particular attention to the vulnerability and coping strategies of global supply chains.