This article examines energy consumption, the transition from organic to fossil energy carriers, and the consequent emissions of CO 2 over a period of almost 150 years (1861-2000) in Italy and Spain. The author's reconstruction and analysis of CO 2 emissions are based on new series of energy consumption including both traditional and modern energy carriers. The article shows that traditional energy carriers should also be taken into account in long run series of pollution intensity of energy use, pollution intensity of the economy, decarbonisation, and other indicators in order to achieve a clearer interpretation of the processes involved. In this work, the authors first present time series of primary energy consumption, final energy consumption, and energy intensities of Italy and Spain for the period 1861-2000. Then several CO 2 indicators for both countries are introduced: total emissions, emissions per capita, pollution intensity of energy (decarbonisation) and pollution intensity. The aim is to investigate whether a decoupling of CO 2 emissions, economic growth, and per capita energy consumption can be observed historically: if so, what the factors underlying this development are. Last but not least, these findings could be used to draw some conclusions on further potential development paths, and notably as to whether it is possible to consume more energy per capita and produce more output per capita at lower levels of emissions. Finally, the authors employ a Divisia index perfect decomposition analysis to scrutinize differences in totalemissions between the two countries. Decomposition analysis, particularly Divisia index based decomposition, has found application in a wide array of fields: aggregate energy indexes, total energy-related CO 2, CO 2 per unit of GDP. To reach an in-depth understanding of the forces underlying different trends in CO 2 emissions, however, decomposition analysis will have to be at the per capita level.