Independent Quality Assessment of Essential Climate Variables: Lessons learnt from the Copernicus Climate Change Service

Abstract If climate services are to lead effective use of information in decision-making enable the transition a climate-smart, climate-ready world, then question trust products and is paramount importance. The Copernicus Climate Change Service (C3S) has been actively grappling with how build such trust; provision demonstrably independent assessments quality products, which was deemed an important element trust-building processes. C3S provides access Essential Variables (ECVs) from multiple sources broad set users ranging scientists private companies decision-makers. Here we outline approach undertaken coherently assess suite observation- reanalysis-based ECV covering atmosphere, ocean, land cryosphere. assessment based on four pillars: basic data checks, maturity datasets, fitness for purpose (scientific cases studies), guidance users. It independently by scientific experts presented alongside datasets fully traceable, replicable transparent manner. methodology deployed detailed, example given. These intended guide ensure they tools that fit answer their specific needs rather than simply first product alight on. This effort develop apply framework consistently all ECVs. Lessons learnt future perspectives outlined potentially improve activities thus services.