Implementing city-level carbon accounting: A comparison between Madrid and London

A change of focus from the current production-based Greenhouse Gas (GHG) emissions inventory to an integrated production-consumption carbon accounting system would improve the quality of city-level inventories. London is one of the few cities in the world which has reported its GHG emission inventory using Consumption-Based (CB) methodologies. Although Madrid has adopted the Global Protocol for Community-Scale Greenhouse Gas Emission Inventories (GPC) to report their GHG emissions, the city has never officially reported its GHG inventory using CB methodologies. Thus, the goal of this study is to analyze the challenges that must be faced by the production-based GHG emission inventory of Madrid in order to estimate GHG emissions from their supply chains and final consumers using the London's GHG emissions inventory experience. From the comparison between the 2010 GHG emission inventories of Madrid and London some challenges could emerge that Madrid's decision-makers might need to face regarding urban carbon accounting practices. As results, this paper shows that if GHG emissions from urban supply chains and final consumers are considered, the total GHG emissions reported by the Madrid inventory could double. This increase is similar to what London experienced when comparing production-based and integrated production-consumption GHG inventories. Besides, some difficulties related to lack of information were found when estimating GHG emissions associated with those goods and services consumed in Madrid. It would be useful to develop a full CB inventory using environmentally extended input-output (EEIO) matrices, more city-level primary data, and local cradle-to-grave factors, following the methodology applied by the London inventory. These actions would allow a more accurate calculation of urban supply chains and final consumer GHG emissions in Madrid. Finally, further research is recommended in order to improve the current knowledge about the contributions of the energy, transport and waste sectors to GHG emissions in both, Madrid and London.