Emission metrics are a fundamental tool for crafting proportional, science-based climate policies. You may have seen them used within the climate sphere before, implicit in statements like “a molecule of methane warms the Earth 28 times more than carbon dioxide.” Emission metrics convert various climate and greenhouse gas parameters to a common scale in order to compare the effects of different greenhouse gases. 

Choice of an emission metric influences how we weigh the impacts of each greenhouse gas. Different metrics lead to different prioritizations for mitigation. In light of these important implications, we must interrogate why we use the metrics we do. The explainer below explores what goes into selecting or calculating an emission metric, how they can fall short, and how they can change our understanding of the climate crisis.