The first results of The Last Millennium Climate Reanalysis, a research project partly funded by CPO’s Climate Monitoring Program, were recently accepted for publication in the Journal of Geophysical Research: Atmospheres. The paper details the framework of the multi-year, multi-institution project, which aimed to produce state-of-the-art reconstructions of the climate for the past millennium using an offline data assimilation approach.

The project’s results show broad agreement with previous reconstructions of Northern-Hemisphere-mean 2m air temperature, with millennial-scale cooling, a multi-centennial warm period around 1000 CE, and a cold period coincident with the Little Ice Age (ca. 1450-1800 CE). Verification against gridded instrumental datasets during 1880–2000 CE reveals greatest skill in the tropics and lowest skill over Northern Hemisphere land areas. Also, verification against independent proxy records indicates substantial improvement relative to the model (prior) data without proxy assimilation.

The offline data assimilation approach used in this project provides a reconstruction of the global mean surface temperature. This approach also reconstructed the spatial distribution and uncertainty in the temperature field and potentially many other fields. Such a record can be used to better diagnose low-frequency climate variability and the statistics of extreme events. Moreover, such a dataset can provide hindcast information against which to measure the skill of models used in decadal climate predictions.

Access the paper:  http://dx.doi.org/10.1002/2016JD024751