Using the mid-Holocene 'greening' of the Sahara to narrow acceptable ranges on climate model parameters

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Authors

Colleges, School and Institutes

Abstract

During the early to mid-Holocene vegetation expanded to cover much of the present-day Sahara. Although driven by a well-understood difference in the orbital configuration, general circulation models have generally failed to simulate the required rainfall increase. One possible explanation is the presence of systematic biases in the representations of atmospheric convection which might also impact future projections. We employ a Bayesian method to learn from an ensemble of present day and mid-Holocene simulations that vary parameters in the convection, boundary layer and cloud schemes. The model can reproduce the “Green Sahara” rainfall if mixing between convective plumes and the environment is increased in the upper troposphere relative to lower down. This does not appreciably impact the present day simulation, meaning that the paleoclimate reconstructions are able to narrow constraints on suitable parameter ranges. This suggests that other uncertain components of climate models could be targeted in this way.

Bibliographic note

Funding Information: P. O. Hopcroft was funded by the EPSRC-funded Past Earth Network Feasibility Study (Grant number EP/M008363/1) and by a University of Birmingham Fellowship. W. Ingram was supported by the Met Office Hadley Center Climate Program funded by BEIS and Defra. This work was carried out using the computational facilities of the Birmingham Environment for Academic Research, http://www.bear.bham.ac.uk and the Advanced Computing Research Center, University of Bristol, http://www.bris.ac.uk/acrc. The authors thank Gethin Williams for installing the climate model code on BEAR. Funding Information: P. O. Hopcroft was funded by the EPSRC‐funded Past Earth Network Feasibility Study (Grant number EP/M008363/1) and by a University of Birmingham Fellowship. W. Ingram was supported by the Met Office Hadley Center Climate Program funded by BEIS and Defra. This work was carried out using the computational facilities of the Birmingham Environment for Academic Research, http://www.bear.bham.ac.uk and the Advanced Computing Research Center, University of Bristol, http://www.bris.ac.uk/acrc . The authors thank Gethin Williams for installing the climate model code on BEAR. Publisher Copyright: © 2021. The Authors.

Details

Original languageEnglish
Article numbere2020GL092043
Number of pages12
JournalGeophysical Research Letters
Volume48
Issue number6
Early online date16 Feb 2021
Publication statusPublished - 28 Mar 2021

Keywords

  • GCM, convection, monsoon, paleoclimate, tuning, uncertainty