Increasing carbon dioxide concentrations in the mesosphere and lower thermosphere are increasing radiative cooling in the upper atmosphere, leading to thermospheric contraction and decreased neutral mass densities at fixed altitudes. Previous studies of the historic neutral density trend have shown a dependence upon solar activity, with larger F10.7 values resulting in lower neutral density reductions. To investigate the impact on the future thermosphere, the Whole Atmosphere Community Climate Model with ionosphere and thermosphere extension (WACCM-X) has been used to simulate the thermosphere under increasing carbon dioxide concentrations and varying solar activity conditions. These neutral density reductions have then been mapped onto the Shared Socioeconomic Pathways (SSPs) published by the Intergovernmental Panel on Climate Change (IPCC). The neutral density reductions can also be used as a scaling factor, allowing commonly used empirical models to account for CO$_2$ trends. Under the“best case’ SSP1-2.6 scenario, neutral densities reductions at 400 km altitude peak (when CO$_2$ = 474 ppm) at a reduction of 13 to 30\% (under high and low solar activity respectively) compared to the year 2000. Higher CO$_2$ concentrations lead to greater density reductions, with the largest modelled concentration of 890 ppm resulting in a 50 to 77 \% reduction at 400 km, under high and low solar activity respectively.