We are developing a laser-based sounding approach for remotely measuring the global concentration of atmospheric CO2 from a satellite. In our method, CO2 abundance is measured by using a three-channel nadir viewing lidar in a 550 km altitude dawn dusk orbit. The CO2 measurement is made utilizing the strong laser echoes from the surface as the lasers are rapidly tuned on and off a selected CO2 line in the overtone band near 1570 nm. A similar technique is used simultaneously on a second channel to measure the surface pressure by utilizing a line in the oxygen A band near 770 nm. The dry-air mixing ratio can be calculated from the ratio of CO2 to O2, that can be measured using a similar technique applied to a line in the O2 absorption band at 770 nm. A third channel operating at 1064 nm is used to detect and screen measurements influenced by cloud and aerosols in the path.