This paper calculates the carbon footprint of the port of Thessaloniki. This calculation is a key criterion for assessing environmental pollution and, more specifically, for determining GreenHouse Gas (GHG) emissions. The calculation was realized using the World Ports Climate Initiative (WPCI) software. It consists of three steps: a) Scope 1: Direct port sources (sources under the direct control and management of the Port Authority), b) Scope 2: Indirect port sources (sources which include whatever was bought by the Port Authority, e.g., state buildings and enterprises), and c) Scope 3: Other indirect sources (sources that are usually connected with the operations of the personnel). The results show that the CO2 sources in the Port of Thessaloniki are mainly the fuel consumption of the merchant ships in the port, the vehicles, the cargo handling equipment, and even the buildings. A first step towards the reduction of CO2 emission could be the installation of solar panels in the port, exploiting the large available areas and conforming to the environmentally friendly policy of the Port of Thessaloniki. In the future, measures should be taken to control the performance of several installations and (constructions and machinery), e.g., the type of equipment, vehicles, cranes, etc. used. Finally, this paper analyzes the climate change phenomenon and the relevant main legislative frameworks valid on a global, European, and national level.