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Climate of the Past An interactive open-access journal of the European Geosciences Union
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Discussion papers
https://doi.org/10.5194/cp-2019-55
© Author(s) 2019. This work is distributed under
the Creative Commons Attribution 4.0 License.
https://doi.org/10.5194/cp-2019-55
© Author(s) 2019. This work is distributed under
the Creative Commons Attribution 4.0 License.

Submitted as: research article 05 Jun 2019

Submitted as: research article | 05 Jun 2019

Review status
This discussion paper is a preprint. It is a manuscript under review for the journal Climate of the Past (CP).

A new multi-variable benchmark for Last Glacial Maximum climate simulations

Sean F. Cleator1, Sandy P. Harrison2, Nancy K, Nichols3, Iain Colin Prentice4, and Ian Roulstone1 Sean F. Cleator et al.
  • 1Department of Mathematics, University of Surrey, Guildford GU2 7XH, UK
  • 2School of Archaeology, Geography and Environmental Science, University of Reading, Whiteknights, Reading, RG6 6AH, UK
  • 3Department of Mathematics & Statistics, University of Reading, Whiteknights, Reading RG6 6AX, UK
  • 4AXA Chair of Biosphere and Climate Impacts, Department of Life Sciences, Imperial College London, Silwood Park Campus, Buckhurst Road, Ascot SL5 7PY, UK

Abstract. We present a new global reconstruction of seasonal climates at the Last Glacial Maximum (LGM, 21,000 yr BP) made using 3-D variational data assimilation with pollen-based site reconstructions of six climate variables and the ensemble average of the PMIP3/CMIP5 simulations as a prior. We assume that the correlation matrix of the errors of the prior both spatially and temporally is Gaussian, in order to produce a climate reconstruction that is smoothed both from month to month and from grid cell to grid cell. The pollen-based reconstructions include mean annual temperature (MAT), mean temperature of the coldest month (MTCO), mean temperature of the warmest month (MTWA), growing season warmth as measured by growing degree days above a baseline of 5 °C (GDD5), mean annual precipitation (MAP) and a moisture index (MI), which is the ratio of MAP to mean annual potential evapotranspiration. Different variables are reconstructed at different sites, but our approach both preserves seasonal relationships and allows a more complete set of seasonal climate variables to be derived at each location. We further account for the ecophysiological effects of low atmospheric carbon dioxide concentration on vegetation in making reconstructions of MAP and MI. This adjustment results in the reconstruction of wetter climates than might otherwise be inferred by the vegetation composition. Finally, by comparing the error contribution to the final reconstruction, we provide confidence intervals on these reconstructions and delimit geographical regions for which the palaeodata provide no information to constrain the climate reconstructions. The new reconstructions will provide a robust benchmark for evaluation of the PMIP4/CMIP6 entry-card LGM simulations.

Sean F. Cleator et al.
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A new multi-variable benchmark for Last Glacial Maximum climate simulations S. F. Cleator, S. P. Harrison, N. K. Nichols, I. Colin Prentice, and I. Roulstone https://doi.org/10.17864/1947.206

Sean F. Cleator et al.
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Short summary
We present geographically explicit reconstructions of seasonal temperature and annual moisture variables at the Last Glacial Maximum (LGM), 21,000 years ago. The reconstructions use existing site-based estimates of climate, interpolated in space and time in a physically consistent way using climate model simulations. The reconstructions give a much better picture of the LGM climate and will provide a robust evaluation of how well state-of-the-art climate models simulate large climate changes.
We present geographically explicit reconstructions of seasonal temperature and annual moisture...
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