*2.1. Methodology*

The aforementioned tools allowed us to carry out and analyze the carbon footprint inventory of products, processes and organizations, based on different standards: ISO 14067 for products, ISO 14069 for corporate footprint or Global Protocol for Greenhouse Gas Emissions (GPC) at scale community for cities. It also enables ecological footprint—Global Footprint Network—and hydric footprint—Water Footprint Network—analyses. The CarbonFeel Initiative has been promoted by the NGO Funciona Foundation for International Collaboration, which facilitates its free use by students of educational institutions that are members of the ResearchFeel alliance for research and teaching. It is a set of solutions that provides a calculation tool called BookFeel, a methodological guide (ProjectFeel) that provides a series of deliverables that ensure total transparency of the calculation [28]. It is structured using the semantic language Footprint Electronic Exchange Language (FEEL) based on the standard XML Schema (XSD) of the World Wide Web Consortium (W3C) and proposes the use of primary data in order to avoid controversial questions about the use of secondary data in the calculation of carbon footprint.

The results are expressed in kilograms of CO2 equivalent [kgCO2-e]. This equivalence is calculated according to the greenhouse effect potential of the main GHGs: carbon dioxide (CO2), methane (CH4), nitrogen oxide (N2O), hydrofluorocarbons (HFCs), perfluorocarbons (PFCs), sulfur hexafluoride (SF6) and nitrogen trifluoride (NF3), all referring to the CO2 effect. The methodology and calculation algorithm of emissions follows the guidelines given by the "Guide for the calculation of the carbon footprint" of the Spanish Office of Climate Change [29]:
