The economic potential of the Northern Sea Route (NSR) as a seasonal Arctic passage between Europe and Asia is controversial. Despite the retreating Arctic Sea ice cover, seasonal shipping along the NSR requires icebreaker support and the utilisation of ice-class ships. To support operational and fleet investment decisions, we analyse the supply dynamics of cargo shipping and icebreaker capacity in the event of growing cargo volumes along the NSR through a system dynamics model till year 2065. In the model, the initial tonnage is based on existing fleet, while hypothetical cargo growth assumes three levels (low, medium and high), and climatic conditions follow three alternative scenarios (melting, baseline and freezing). The model results indicate that over 30 million tonnes of cargo p.a. would be needed to maintain a sustainable level of traffic in the NSR, compared to less than 4 million tonnes in 2014. During the modelled 50-year-period, on average 24 to 44 per cent of potential NSR cargo volume will be lost due to ageing icebreakers and ice-classed fleets and the slow newbuilding pace. The findings suggest that NSR’s economic potential for global shipping is likely to remain marginal for decades to come because of its inherent constraints.