WHAT IS ACRE The international Atmospheric Circulation Reconstructions over the Earth (ACRE) initiative works to retrieve our global climate history. It harnesses the work of many professionals and volunteers to recover historical terrestrial and marine weather observations. Project members search out millions of documents, typically paper-based, convert them to electronic images and then digitise the useful data they contain. The data supports computer-based 4D weather recon- structions (reanalyses) spanning the last 200-250 years. Climate applications and analyses of climate impacts worldwide benefit from the work of the ACRE initiative. All of the historical surface weather data and the reanalyses are freely available. ACRE achieves its mission by: • linking international meteorological organisations & data rescue infrastructures; • facilitating the recovery, extension, quality control & consolidation of global historical terrestrial & marine instrumental surface data covering the last 250 years; • making these observations available to all international reanalyses; • ensuring that 4D reanalysis products can be tailored/downscaled to flow into various climate applications & production models. • providing access to tools and techniques for analyses and interpretation of historical documentary weather observations.