On a single variable (carbon), dated, based on the direct and indirect impacts of an entity (person, company, town, country) and not standardized.
A company's carbon footprint encompasses direct emissions (scope 1), which are owned or controlled by the company, such as burning fossil fuels for transportation or energy, and indirect emissions (scope 2 and 3), which are consequences of the company's activities but originate from sources not owned or controlled by it. It is a snapshot at a given moment of the carbon impact of a company's activities only. It includes its own consumption of fossil energy, the consumption (or purchase) of products, materials or services, and the marketing of potentially emitting products or services.
Multi-varied (max 14 impact criteria), focuses on a function ("produce 1kg of H2") delimited on a closed system and meets the ISO14040 standard.
The LCA of a product or a process allows to evaluate the global environmental impact (water consumption, fertilizers, carbon...) throughout its life time. It can account for multiple stages depending on the system boundaries, such as Extraction, Production, Transport, Use and End of life. It allows to evaluate the co-benefits of the solutions. As it focuses on a function, it allows to compare two solutions to the same problem.