A contradiction exists between high CO2 emissions from primary Mg production and emission mitigation by Mg applications in the life cycle of automobiles. Previous studies have not completely considered the technological improvements and energy switching of the Pidgeon process in China in the calculation of the Mg production stage. In the current study, the estimation of CO2 emissions from the Pidgeon process is conducted by using updated on-site data and four energy scenarios. Moreover, three allocating methods are employed because of the utilization of waste gases generated in the symbiosis system of Mg ingot and coke/semi-coke. Depending on the allocation methods, calculated CO2 emission from the Pidgeon process is 21.6-26 t/t-Mg, which is 38-48% less than the previous estimation. To clarify the CO2 emission reducing effect of Mg application in automobiles, the calculated results are applied in a generic car and compared with other data sources of the Pidgeon process. Furthermore, the mitigation gap between Mg and Al substitutes for steel in automobile is discussed. Result shows that an improved Pidgeon process will facilitate the substitution of Mg for steel in automobile application in terms of life cycle CO2 emission but will remain inferior to Al application in automobiles. Nevertheless, with the further improvement of technologies in the Pidgeon process, CO2 emission with regard to primary Mg production is estimated to decrease by 18%, thus resulting in a further CO2 emission reduction of 0.388 t in the automobile life cycle. (C) 2015 Elsevier B.V. All rights reserved.