Increasing carbon dioxide causes cooling in the upper atmosphere and a secular decrease in atmospheric density over time. With the use of the Whole Atmospheric Community Climate Model with thermosphere and ionosphere extension (WACCM-X), neutral thermospheric densities up to 500 km have been modelled under increasing carbon dioxide concentrations. Only carbon dioxide and carbon monoxide concentrations are changed between simulations, and solar activity is held low at F10.7 = 70 throughout. Using the four Representative Concentration Pathway (RCP) carbon dioxide scenarios produced by the Intergovernmental Panel on Climate Change (IPCC), scenarios of neutral density decrease through to the year 2100 have been modelled. The years 1975 and 2005 have also been simulated, which indicated a historic trend of -5.8% change in neutral density per decade. Decreases in the neutral density relative to the year 2000 have been given for increasing ground-level carbon dioxide concentrations. WACCM-X shows there has already been a 17% decrease in neutral densities at 400 km relative to the density in the year 2000. This becomes a 30% reduction at the 50:50 probability threshold of limiting warming to 1.5 degrees Celsius, as set out in the Paris Agreement. A simple orbital propagator has been used to show the impact the decrease in density has on the orbital lifetime of objects travelling through the thermosphere. If the 1.5 degrees Celsius target is met, objects in LEO will have orbital lifetimes around 30% longer than comparable objects from the year 2000.