An international team from the U.K., China, Japan and the U.S. has addressed the challenges of recovering, collating, digitizing and working with long-term instrumental weather observations in in the East Asian Region. Historic instrumental weather observations are critical in extending the knowledge of past weather and climate and for comparison with paleo-proxy data. The potential of such data is shown to best effect when assimilated into dynamical 4-D global reanalyses to reconstruct weather and climate patterns and fluctuations over 200+ years, creating a spatially and temporally complete database of global weather that is used for improving climate projections and contributing to climate change detection and attribution studies.