The international Atmospheric Circulation Reconstructions over the Earth (ACRE) initiative undertakes and facilitates the recovery and digitisation of global, historical surface terrestrial and marine weather observations. The digitised data underpins 3D weather reconstructions (reanalyses) spanning the last 200-250 years. All of the historical weather data and the resulting climate reanalyses are freely available to researchers with interests in climate science, applications, impacts, risks and extremes. ACRE also has a cross-disciplinary focus, melding climate science with the social sciences and humanities. It aims to tailor historical weather reconstructions to the needs of educators, students and the general public. ACRE achieves this outcome by linking international meteorological organisations & data rescue groups to facilitate the recovery, digitisation, extension, quality control & consolidation of global historical terrestrial & marine instrumental surface data covering the last 250 years. The data are stored in publically accessible, consolidated databanks, making the observations freely available as input to reanalysis systems that create detailed 3D reconstructions of weather history. ACRE also works to ensure that the outputs of the reanalysis systems can be tailored (downscaled) to seamlessly flow into various climate applications & production models. ACRE is run from the Met Office Hadley Centre, but relies on the continuation of ‘grassroots’ support from the international weather/climate data community and some funding and in kind support from a core consortium of nine partners: University of Southern Queensland (Australia) Met Office Hadley Centre (MOHC) (UK) National Oceanic and Atmospheric Administration NOAA (US) Earth System Research Laboratory (ESRL) and Cooperative Institute for Research in Environmental Sciences (CIRES), University of Colorado (US) NOAA's National Centers for Environmental Information (NCEI) International Environmental Data Rescue Organization (IEDRO) University of Sussex (UK) British Library University of Giessen (Germany) University of Bern (Switzerland) See also Graphic presentation of ACRE activities Bulletin of the American Meteorological CLICK to download this image Society article outlining ACRE ACRE History In 2006, climate applications scientists in Queensland, Australia, asked if a longer and more complete historical weather record could be created and fed directly into various crop, pasture, and production models. Existing dynamical reanalyses were steps toward such a product, but they spanned only the last six decades and had well-known shortcomings. To meet the needs of application scientists, new reanalyses would have to extend much further back in time while maintaining accuracy with limited observations. They would also need to be disseminated in a way that is easy to use directly and to downscale to small regions. At the same time researchers at the National Oceanic and Atmospheric Administration (NOAA), the University of Colorado, the National Center for Atmospheric Research (NCAR), and the European Centre for Medium-Range Weather Forecasts (ECMWF) were independently pursuing the controversial idea of reanalyses extending back to the nineteenth century using only surface weather observations. As these researchers demonstrated that such input reanalyses were feasible, an international reanalysis workshop considered the issues of overall improvements for climate applications. To implement these ideas would require new work on data assimilation, extensive efforts to recover worldwide historical weather observations, and new ways of distributing and utilizing large gridded reanalyses. The Atmospheric Circulation Reconstructions over the Earth (ACRE) initiative was then established by Rob Allan of the UK Met Office, Hadley Centre with the goal of facilitating such research by coordinating existing national and international projects, and also encouraging and undertaking the additional work needed to produce and use reanalyses for climate applications. ACRE Recognition “ I am writing to express my appreciation of the important work you have been undertaking to support the work of the International Surface Pressure Databank (ISPD), a key repository for global surface pressure datasets… I commend the efforts by you and your colleagues to rescue, digitize and homogenize global and marine surface pressure data … ” Dr. Carolin Richter, Director, Global Climate Observing Systems Secretariat, World Meteorological Organisation

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