[en] We study changes in the aggregate carbon intensity (ACI) for electricity at the global and country levels. The ACI is defined as the energy-related CO_2 emissions in electricity production divided by the electricity produced. It is a performance indicator since a decrease in its value is a desirable outcome from the environmental and climate change viewpoints. From 1990 to 2013, the ACI computed at the global level decreased only marginally. However, fairly substantial decreases were observed in many countries. This apparent anomaly arises from a geographical shift in global electricity production with countries having a high ACI increasingly taking up a larger electricity production share. It is found that globally and in most major electricity producing countries, reduction in their ACI was due mainly to improvements in the thermal efficiency of electricity generation rather than to fuel switching. Estimates of the above-mentioned effects are made using LMDI decomposition analysis. Our study reveals several challenges in reducing global CO_2 emissions from the electricity production sector although technically the reduction potential for the sector is known to be great. - Highlights: •Variations of aggregate carbon intensity (ACI) for electricity of world countries are analysed. •Main drivers of changes in ACI of major electricity producing countries are studied using index decomposition analysis. •Geographical shift in electricity production had a significant impact on global ACI. •Improvements in the thermal efficiency of generation were the main driver of reduction in ACI.