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With network expansion, the energy consumption and CO2 emissions associated with networks are increasing rapidly. In this paper we propose an approach for energy minimization in IP over WDM networks and furthermore propose the use of renewable energy to further reduce the CO2 emissions at a given energy consumption level. We develop a Linear Programming (LP) model for energy minimization in the network when renewable energy is used and propose a novel heuristic for improving renewable energy utilization. Compared with routing in the electronic layer, routing in the optical layer coupled with renewable energy nodes significantly reduces the CO2 emission of the IP over WDM network considered by 47% to 52%, and the new heuristic introduced hardly affects the QoS. In order to identify the impact of the number and the location of nodes that employ renewable energy on the non-renewable energy consumption of whole network, we also constructed another LP model. The results show that the nodes at the center of the network have more impact than other nodes if they use renewable energy sources. We have also investigated the additional energy savings that can be gained through Adaptive Link Rate (ALR) techniques where different load dependent energy consumption profiles are considered. Our optimized REO-hop routing algorithm with renewable energy and ALR results in a maximum energy saving of 85% (average of 65%) compared to a current network design where all nodes are statically dimensioned for the maximum traffic in terms of IP ports and optical layer and hence consume power accordingly. Furthermore, when all the nodes have access to typical levels of renewable power we show that the associated reduction in non-renewable energy consumption reduces the network's CO2 emissions by 97% peak, 78% average.