Using the CO2 emission, energy consumption, real GDP and population size from 1971-2010, and applying the Logarithmic Mean Divisia Index (LMDI) multiplicative decomposition formulation we partition the CO2 emission into (1) population effect due to population change, (2) real output or economic activity effect via change in real GDP, (3) energy intensity effect emanating from efficiency in its usage, (4) substitution effect arising from energy substitution and (5) coefficient effect derived from reduced emissions per unit of energy. At the global level, the decomposed results show that the increase in CO2 emission worldwide comes mainly from the increase in the population effect, the economic activity effect, and the coefficient effect. It is also shown that the energy intensity and energy substitution effects play a key role in decreasing CO2 emission. Viewed from the regional perspective, the CO2 emission in Asia, Africa, and the Middle East have increased during the last 40 years and have increased more during the last 10 years. The main causes of increase in CO2 emission in these 3 regions are due to economic activity and population increase. The decomposed results show that the CO2 emission in Europe and America have slowed down during the last 40 years; the improvement in energy intensity and energy substitution are the main causes of decrease in CO2 emission in these 2 regions.