To meet the targets of the Paris agreement, telecom operators, as other industries, need to set targets on their emission reduction to arrive at a net zero situation as reported in Recommendation [b-ITU-T L.1470]. In a moment in which the network traffic will increase, this Recommendation defines a KPI useful to evaluate network emission and give an indication on how a network reduce it emission due to the energy usage. This Recommendation defines a KPI called Network Carbon Intensity energy NCIe; also, it defines how to apply the Recommendation: which part of the network is covered and finally how to calculate the metric and continuously in network evolution. This Recommendation also defines correlation between the carbon intensity indicator and energy efficiency metric. The carbon KPI defined in this Recommendation refers to the energy efficiency metric defined in [ITU-T L.1331].