Purpose – Urban areas are responsible for significant amounts of greenhouse gas (GHG) emissions, but cities can have quite different values of carbon footprints. The purpose of this paper is to identify the determinants of urban GHG emissions in order to explain these differences. Design/methodology/approach – Seven global cities – Bangkok, Chicago, London, Madrid, Mexico City, Milan and New York City – have been included in the paper's sample. These cases have been chosen in order to represent a variety of characteristics and contexts of developed and developing countries and according to data availability. A first level of analysis regards local GHG emission inventories, which attribute emissions to activity sectors. Sectorial emissions are then evaluated to quantify the relevance of several determinants: climate conditions, urban form, economic activities in place, state of technology, mobility and housing infrastructures and costs, and income and life style. Findings – Determinants show different weights in influencing behaviours at city level, and ultimately depend on economic, technical, social and cultural factors. Beside a significant role of climate conditions, urban density appears as the main determinant in shaping residential emissions from direct fuel consumption, whereas, for electricity, consumption patterns and technological features of power generation play a major role. For ground transport, urban form affecting mobility patterns and technological features of the vehicle stock stand out as the most significant determinants.