The European Union tightened its climate targets in July 2021. Sectors of the economy – including ports – must contribute by reducing their emissions. This paper strives welfare economics by including externalities such as environmental costs and presents results for evaluating infrastructure investments in ports. By applying a combined cost-benefit and carbon footprint analysis the authors show how decision-makers can assess port investments in infrastructure economically and environmentally. Using European port redevelopment as an example, this article illustrates that including externalities in the cost comparisons of port investment options could lead to new discussion making. Moreover, decarbonizing the economy does not just bring only economic benefits by efficiency increase but can also reduce cost to society. The idea of the triple bottom line (TBL) framework is addressed and discusses the role of the inclusion of social sustainability for port infrastructure investments.