The carbon footprint (CF), or also referred to as the GHG footprint, deals with the carbon component and accounts for anthropogenic greenhouse gas emissions associated with the production of goods or services, a specific event or an entire organisation, depending on the aim. Inconsistent terminology is also a concern here, with some authors calling it “carbon accounting”, even if they determined a carbon footprint. The carbon footprint method should also not be confused with GHG accounting, which is an inventorying of emissions, at least in the publications that were reviewed for this report. Adding to the confusion is that carbon is sometimes used as a catch all term for GHG emissions, such as carbon dioxide, methane, and nitrous oxide, which are all expressed in carbon dioxide (CO₂) equivalents.

The analysis of a CF “follows the same basic modeling principals as the EF, but only considers the greenhouse gas (GHG) emissions for the evaluation of the environmental impacts” (Beloin-Saint-Pierre et al. 2016). There are three main accounting approaches for GHG emissions on the city scale, which are 1) territorial (geographic)-based, 2) trans-boundary community-wide infrastructure and 3) consumption-based accounting (Chavez and Ramaswami 2013). The territorial approach, also called production-based (PB) accounting, “measures emissions generated in the place where goods and services are produced. However, the growth of emissions embodied in trade has raised the question whether we should switch to, or amalgamate PB accounting, with other accounting approaches. Consumption‐based (CB) accounting has so far emerged as the most prominent alternative. This approach accounts for emissions at the point of consumption, attributing all the emissions that occurred in the course of production and distribution to the final consumers of goods and services“ (Afionis et al. 2017) and uses household expenditure data most often, although input-output tables adjusted from national to urban scales are also used (Ramaswami et al. 2011). The trans‐boundary infrastructure supply chain footprint (TBIF) was developed by Ramaswami et al. (2008) and is a demand-centered hybrid LCA-based inventory method for GHG emissions of cities. “The TBIF method utilizes the concept of scopes from corporate GHG emissions accounting protocols to include both in‐boundary and trans‐boundary GHG emissions associated with key community‐wide activities; hence it has also been referred to as an expanded geographic inventory or a community‐wide infrastructure GHG footprint. The TBIF method recognizes that cities include both producers and consumers, and focuses on infrastructure supply chains that serve the entire community as a whole. The GHG emissions accounted for by the TBIF method are (1) direct in‐boundary GHG emissions (scope 1), (2) indirect GHG emissions from the generation of purchased electricity (scope 2), and (3) GHG emissions from essential trans‐boundary infrastructures serving cities (scope 3), such as water supply, transportation fuels, airline and commuter travel, and other critical supply chains. The inclusion of trans‐boundary infrastructures (scope 3) warrants careful allocation of GHGs to avoid double counting (Ramaswami et al. 2008)” (Chavez et al. 2012).