The effects of CO 2 ppm in troposphere on both spectral and total emissivity are reviewed using several methods. The compared models are by Hottel [2], Bliss [3], Atwater and Ball [4,6], wide Band Model by Edwards [5], Yamamoto and Sasamori [6,7], and using HITRAN data base [8]. For spectral emissivity, the results by Yamamoto and Sasamori match well with predictions using HITRAN data base. For total emissivity, the deviations between models are rather large and sometimes more than about 0.05. In general, for a given condition, the upper bound of total emissivity is given by Hottel, and lower bound is given by HITRAN. The predictions by Edwards are in between but near to those of Hottel. The CO 2 ppm varied from 300 ppm to 600 ppm, temperature varied from 220K to 300K, and pressure from 0.3 to 1.0atm. As CO 2 ppm increases, the total emissivity increases. For a given CO 2 ppm, the total emissivity increases as the air thickness increases which are also true for both temperature and pressure increase. Around 260K, the total emissivity is less sensitive to increasing temperature than to decreasing temperature. For a given pressure change, the total emissivity values by wide band model changes more than the values by HITRAN. The reverse is true for temperature change.