The aim of the present thesis is to analyse the existent relationship between productive activities and CO2 emissions generated in Ecuador. On the basis of the input-output approach, three chapters are developed allowing a better understanding of this relationship. The first chapter identifies the key sectors in CO2 emissions for the Ecuadorian economy by 2013. The results show that 19 of the 71 productive activities are the most influential in the CO2 emissions generation. Of the 19 activities 8 can be considered as key sectors. The 8 activities are responsible for 60% of the total emissions generated by the productive apparatus; and, 4 of them belong to the services sector, making the last a relevant sector for the analysis of the CO2 emissions generation in the Ecuadorian economy. The second chapter deepens the analysis of the CO2 emissions generated by the activities belonging to the services sector, for which the methodology named "input-output subsystems" is used. This technique allows the identification of several components through which the total emissions (direct and indirect) of a sector or group of sectors are generated. The results show that the emissions directly attributable to the services sector are strongly concentrated in the transport and storage activities. However, However, in the case of other service activities, they have strong pull effect on other activities of the economy. In this respect, activities such as trade, telecommunications, real estate services or government administration, which would be relevant to the design of mitigation policies. The third chapter analyses the factors that are behind the evolution of the CO2 emissions of the services sector in Ecuador between 2007 and 2013. For this, the analysis of input-output subsystems is combined with structural decomposition analysis. The disaggregation of effects presented in this study is greater than that obtained in similar applications, due to the methodology used in the analysis of subsystems. This disaggregation shows results that facilitate the understanding of the elements and the causes that are behind the variation of CO2 emissions of the activities belonging to the services sector. The results indicate that although the expansion of demand is the main cause for the increase of the emissions, there are important asymmetries in the behaviour of the activities of the services sector and the causes that generate those emissions. It is evidenced that some activities show improvements in terms of efficiency and technology which, in some way, compensate the increase in emissions caused by the demand effect. However, other activities, increased their emissions not only due to an upsurge in the demand but also given a deterioration in terms of efficiency and technology.