The inverse problem of reconstructing the vertical profiles of CO2 in the atmosphere by IR–spectra of the solar light transmission is investigated. To solve this problem, we propose the two-stage method. On the first stage, we use the modified Tikhonov method. On the second stage, to approximate a solution of the regularized equation, we apply the modified Gauss–Newton method. The convergence theorem is formulated and the numerical results for a few of measured spectra are presented.