This study uses three methods to explore the roles of the carbonization index and energy intensity in the formation of CO2 emissions throughout the world based on statistics from 1971 to 2000. The finding is that the role of both the carbonization index and energy intensity is the same in the formation of CO2 emissions. That is, they decreased CO2 emissions. However, the decrease of CO2 emissions caused by energy intensity is larger than the decrease of CO2 emissions caused by the decarbonization index. The estimated rates of the former to the latter are four times larger.