Reliable wave resource characterization is necessary for the accurate estimation of available resources. However, a minimum of 10 years has been recommended for such analysis, considering the impact of changing climate on the selection of a suitable period for wave energy assessment is necessary. Hence, in this work, we used more than five decades of wave characteristics simulated globally to investigate the role of selecting the period of wave energy assessment in the estimation of available resources. For this purpose, the numerical simulation of waves was carried out globally using Simulating WAves Nearshore (SWAN) model forced with global re-analysis wind data, JRA-55, developed by Japan Meteorological Agency (JMA). The performance of the model was investigated using ERA-5 reanalysis wave data. Comparison of monthly mean wave characteristics showed a reliable performance of SWAN at a global scale, even though the model has been developed for nearshore wave modeling purposes. The validated model was then used to generate the wave characteristics for 55 years. The wave characteristics in 5 decades were analyzed not only intra-annually but also on a multi-decadal scale. In addition, the wave climate and wave energy were obtained at different time scales, and the results were compared with 55-yearly wave climate, and the impact of selecting different intervals was discussed. Moreover, the relationship between the change of different wave parameters and the change of wave energy in the long-term was assessed.