As pressure on investors to decarbonize their portfolios continues to mount, the importance of Scope 1 and 2 carbon intensity will only increase. In this paper, we survey the current state of corporate carbon disclosure and explore the challenges facing investors in using estimation strategies. We propose an improved estimation strategy, combining the strengths of several existing methodologies, and introduce a new FTSE Russell carbon emission dataset for c. 10,000 companies based on a hierarchical, multi-model approach.