Strategies for climate change mitigation in European cities have become more urgent and require actions to proactively involve administrators, citizens and other stakeholders and let them cooperate to accomplish widely approved plans for decarbonisation. Nevertheless, considering the short term of political mandates and the instability of social-economic-legal variables in our changing world, urban planning practices will require more effective and rapid decision support systems to easily access and process information. The paper presents an optimised carbon accounting methodology to assess greenhouse gas (GHG) emissions in specific urban environments and inform urban policies and design. In particular, this procedure, substantially inspired by the IPCC standard methodology for GHG emissions inventory of Nations, constitutes the framework of a “mediate model” with a dual role: to both assess the Carbon Footprint of urban neighbourhoods and to estimate the effects, in terms of Carbon Footprint mitigation, of action plans addressed to carbon neutrality. For demonstration, the carbon accounting framework has been performed based on average European values. The procedure started by profiling the typical household as functional unit, whose carbon footprint has been estimated 6.93 t CO2-eq/yr, referring to energy use for housing and mobility, domestic waste treatment and water use. The impact of the average European neighbourhood has been obtained by scaling up to 10,000 households (23,000 inhabitants) as benchmark for future applications. An additional outcome concerns the innovative spatial visualisation of results in terms of equivalent forestland (e.g. the emission of one average European household corresponds to the quantity of CO2 yearly absorbed by 0.51 ha of forest), that allows for understanding intensity and size of impacts in order to consistently support awareness raising initiatives targeting citizens and stakeholders and communication-dissemination activities.