Recently, network operators around the world reported statistics of network energy requirements and the related carbon footprint, showing an alarming and growing trend. Such high energy consumption can be mainly ascribed to networking equipment designed to work at maximum capacity with high and almost constant dissipation, independent of the traffic load. However, recent developments of green network technologies suggest the chance to build future devices capable of adapting their performance and energy absorption to meet actual workload and operational requirements. In such a scenario, this contribution aims at evaluating the potential impact on next-generation wireline networks of green technologies in economic and environmental terms. We based our impact analysis on the real network energy-efficiency targets of an ongoing European project, and applied them to the expected deployment of Telecom Italia infrastructure by 2015-2020.