The polar summer thermal structure, with its cold mesopause and steep temperature gradients, both below and above the mesopause, produces the largest non-LTE effects in the CO2 ν2 mode manifold states. In this paper we focus on validating the non-LTE model applied for operational temperature retrievals from the SABER 15 ¿m limb radiance observations for these extreme conditions. We demonstrate that accounting for the redistribution of ν2 quanta among various CO2 isotopes shifts the retrieved summer 2002 polar mesopause altitude upwards by 2 to 4 km. It brings the SABER temperature measurements into a better agreement with those of falling sphere experiments, lidar observations, as well as with climatological data.