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Traffic variation heavily impacts energy savings achieved by putting Line Cards (LCs) into Sleep Mode (SM) in core Internet Protocol (IP)-over-Wavelength Division Multiplexing (WDM) networks. We propose a simple traffic model covering temporal and spatial traffic variation and investigate the impact of (controlled) traffic variations on energy savings achieved with the Energy Watermark Algorithm (EWA) as well as on devices lifetime in realistic network scenarios. The results indicate that spatial variation of traffic is no obstacle in saving energy in the networks. We point out the need for consistent routing schemes between the reference network (designed with a sophisticated Mixed-Integer Linear Programming (MILP) formulation in our case) and the solutions computed dynamically during network operation (with the lifetime-unaware EWA in our case).