Extensive measurements of macroscopic stress in a 2D LJ glass, over a broad range of temperatures ($T$) and strain rates ($\dot\gamma$), demonstrate a very significant decrease of the flowing stress with $T$, even much below the glass transition. A detailed analysis of the interplay between loading, thermal activation, and mechanical noise leads us to propose that over a broad ($\dot\gamma,T$) region, the effect of temperature amounts to a mere lowering of the strains at which plastic events occur, while the athermal avalanche dynamics remains essentially unperturbed. Temperature is then shown to correct the athermal stress by a (negative) additive contribution which presents a universal form, thus bringing support to and extending an expression proposed by Johnson and Samwer [1]. Our prediction is shown to match strikingly well numerical data up to the vicinity of $T_g$.