ABSTRACT - The „Internet“ with all associated applications and technologies is one of the world’s major contributors to CO2 emissions and energy consumption. While AI algorithm training and hyper scale Data Centers are certainly on top of the list the contribution of transporting the data to / from its users is not negligible. The pressure on Telco Operators to reduce their direct and indirect (!) CO2 footprint is severely increasing. Moreover, energy costs for operating these networks are already the major OPEX factor. As the amount of data to be transported will not decrease but certainly increase it is crucial to utilize transport technologies with the lowest possible energy consumption. After other studies have focused e.g. on Access Networks, we will here focus on Metro Transport Networks which are used for front / mid / backhauling mobile traffic, backhauling residential (e.g. FTTx, xDSL) or enterprise customer traffic, interconnecting data centers etc over distances up to approx. 80km. Those networks rely on two fundamentally different data transport technologies, so called Active (WDM) Transport Systems versus Passive (WDM) Transport. We will look into the details of Metro Data Transport and compare Active vs Passive Transport means in respect to their power consumption per link (end to end). Utilizing Passive Transport allows energy saving beyond a factor of 100 (!) per link compared to transporting the same amount of data with Active Systems.