Is sharing truly caring? Environmental data value chains and policymaking in Europe and Central Asia

•The Shared Environmental Information System (SEIS) aim to expand the access to environmental data.•SEIS has had a significant and positive impact on the production and harmonisation of environmental indicators.•Data harmonization problems (e.g., data collection, definitions, and legislation) remain throughout the pan-European region.•Non-evidence-based policymaking highlight a disconnect between data production and data use.•Need to improve our understanding of the political and behavioural determinants of data use.