We address the vibration monitoring problem as the double task of detecting damages seen as changes in the modal structure of a linear dynamic system and localizing the detected damages within the monitored structure. The authors have already presented a statistical damage detection test based on a residual derived from the covariance subspace identification method. This method has been extensively tested and shown good results on a number of real mechanical structures. Nevertheless, in real life applications, effects of environmental variables such as temperatures can be at least as significant as the damage itself. The paper is focused on presenting a simplified relation between the relevant modal parameters and the temperature. We explain how the temperature influences the stiffness, and thus the modal parameters. Finally, we discuss modifying our damage detection test in order to reject the temperature as a nuisance.