The impact of doubled CO2 on the vertically propagating migrating diurnal tide in the mesosphere is studied using the Canadian Middle Atmosphere Model (CMAM), a coupled chemistry-climate model that extends from the Earth's surface to the lower thermosphere. A linear tidal model forced by the tidal heating from the CMAM is used to attribute cause and effect. The CMAM results exhibit a tidal temperature amplitude increase of up to 2 K in the equatorial upper mesosphere. This is attributed primarily to an increase in tropospheric solar heating which results from an increase in water vapor. Changes in stratospheric solar heating, radiative damping, tropospheric latent heating, background atmosphere, and clouds are found to have little impact.