We present an in-depth decomposition analysis using physical indicators of trends in Carbon dioxide (CO2) emissions in the cement industry in Brazil, China, South Korea and the United States. Physical indicators allow a detailed analysis of intra-sectoral trends, in contrast to the often used monetary indicators. We assess the contribution of different factors affecting CO2 emissions in the cement industry, including change in product mix, efficiency of power generation, changes in fuel mix and changes in energy efficiency. The decomposition results show that in all examined countries, increased production was the main contributor to the increase in total CO2 emissions. Energy-efficiency improvement is the most important factor that led to the reduction of emission intensities for all countries except Korea. For Korea, structural change in the product mix is the most important factor contributing to the emission intensity reduction.