The problem of middle atmosphere and lower ionosphere response to anthropogenic greenhouse gases increase is considered on the basis of the INM RAS coupled troposphere-stratosphere-mesosphere and ionosphere D region model. The model is based on three-dimensional atmospheric general circulation model (AGCM) with hybrid vertical coordinate system (0-90 km), which is development version of AGCM unit of INMCM climate model. A simple five-component photochemical model was used as a model of lower ionospheric chemical transformation. Numerical experiments for reproduction of atmospheric climatic characteristics with different CO₂ total content were carried out to quantify the long-term response of upper atmosphere and ionosphere sensitivity. It was shown that the mean global state and variability of the undisturbed lower ionosphere for this model is essentially determined by the neutral temperature field in the mesosphere, so the changes in global mean temperature values as well as in regional features of temperature variability (first of all in structure and amplitudes of nonmigrating tides) control a sensitivity of dayside electron concentration to anthropogenic forcing.