The objective of the SAG GHG is to ensure the coordination of the observational network that provides long-term “climate-quality” data on trends and spatial distributions of long-lived (LL) GHGs and related tracers. Data are used to calculate changes in radiative forcing since the pre-industrial era, to constrain LLGHG budgets of emissions and losses at global to regional spatial scales, and to verify bottom-up emission inventories and process models.