This article analyses how mechanisms and governance for reducing agri-food GHG emissions are evolving, and how this influences sustainability outcomes. It examines how emerging greenhouse gas (GHG) accounting systems are reshaping environmental governance within the UK agri-food sector. Through an ecosystem perspective, we explore how farm-level carbon accounting is developing at the intersection of public policy, private markets, civil society and knowledge networks The paper applies a novel 4C ecosystem framework for analysing the GHG accounting landscape. The results highlight the emergence of hybrid public–private governance, shaped by two distinct compliance streams: market-led supply chain requirements and state-led agri-environment. This research was carried out by researchers at the Countryside and Community Research Institute (CCRI), University of Gloucestershire, UK, as part of the Land Use Net Zero, Nature and People (LUNZ) FOOTPRINT project. https://lunzfootprint.com/