A natural extension of the physical input-output tables is the inclusion of environmentally relevant materials, which is done in the environmentally-extended input-output analysis (EE-IOA). While it can be argued that all materials have an environmental impact, it is those that have a direct influence on e.g. environmental pollution, climate change, degradation of natural resources and biodiversity loss as a result of economic activities that are quantified (Kitzes 2013). Since they include direct and indirect material (or energy) flows they can be very well expressed as environmental impact indicators such as carbon or water footprints, for which many studies exist, with a handful on cities (Beloin-Saint-Pierre et al. 2016; Dias et al. 2014).

An advantage of the EE-IOA method is that it can identify the sectors responsible for the largest share of environmental burden, as it links environmental data (e.g. carbon dioxide emissions) with monetary flows. However, since “the input-output model is in monetary units and the environmental extension is in physical units (e.g. in joules of energy, tons of material, or kilograms of pollutant), this integration is non-trivial” because of the required assumptions that IOA makes around homogenous products, prices and the exclusion of non-market flows (Schaffartzik et al. 2014, 1). Several other strengths and weaknesses of this method are listed in the category overview table.