Equivalence—A Useful Yet Complex Concept in Natural Resource Science

The concept of equivalence is widely employed to aggregate different types of resource depletion or emissions. The practice offers convenience for reporting and can assist policymaking. However, equivalence is typically established using a model based only on selected criteria. If alternative criteria are used, the relative importance of different types of resource depletion or emissions can change. This communication addresses the subject of greenhouse gas (GHG) emissions and carbon dioxide equivalence (CO 2 e). Using the Australian beef cattle and sheep meat sectors as a case study, radiative forcing (RF) footprints were quantified, and a method is presented to express these as CO 2 e emissions rather than the units W/m 2 . RF footprints are an alternative way of aggregating GHG emissions. They incorporate RF from current-year emissions and RF from historical emissions that remain in the atmosphere, avoiding the need to choose an arbitrary time horizon. There is simplicity and familiarity associated with the CO 2 e unit. However, it is concluded that whenever GHG emissions are reported as CO 2 e emissions, there is a need for transparency about the basis for equivalence, justification of the approach, as well interpretation of the results, and potential implications of selecting other bases of equivalency.