Submitted as: development and technical paper
07 Sep 2022
Submitted as: development and technical paper | 07 Sep 2022
Status: a revised version of this preprint is currently under review for the journal GMD.

UKESM1.1: Development and evaluation of an updated configuration of the UK Earth System Model

Jane Patricia Mulcahy1, Colin G. Jones2,3, Steven T. Rumbold2,4, Till Kuhlbrodt2,4, Andrea J. Dittus2,4, Edward W. Blockley1, Andrew Yool5, Jeremy Walton1, Catherine Hardacre1, Timothy Andrews1, Alejandro Bodas-Salcedo1, Marc Stringer2,4, Lee de Mora6, Phil Harris7, Richard Hill1, Doug Kelley7, Eddy Robertson1, and Yongming Tang1 Jane Patricia Mulcahy et al.
  • 1Met Office Hadley Centre, Exeter, UK
  • 2National Centre for Atmospheric Science, UK
  • 3School of Earth and Environment, University of Leeds, UK
  • 4Department of Meteorology, University of Reading, Reading, UK
  • 5National Oceanography Centre, Southampton, UK
  • 6Plymouth Marine Laboratory, Plymouth, UK
  • 7UK Centre for Ecology and Hydrology, Wallingford, UK

Abstract. Many CMIP6 models exhibit a substantial cold bias in global mean surface temperature (GMST) in the latter part of the 20th century. An overly strong negative aerosol forcing has been suggested as a leading contributor to this bias. An updated configuration of UKESM1, UKESM1.1, has been developed with the aim of reducing the historical cold bias in this model. Changes implemented include an improved representation of SO2 dry deposition along with several other smaller modifications to the aerosol scheme and a retuning of some uncertain parameters of the fully coupled Earth System Model. The Diagnostic, Evaluation and Characterization of Klima (DECK) experiments, a 6-member historical ensemble and a subset of future scenario simulations are completed. In addition, the total anthropogenic effective radiative forcing (ERF), its components and the effective and transient climate sensitivities are also computed. The UKESM1.1 pre-industrial climate is warmer than UKESM1 by up to 0.75 K and a significant improvement in the historical GMST record is simulated with the magnitude of the cold bias reduced by over 50 %. The warmer climate increases ocean heat uptake in the northern hemisphere oceans and reduces Arctic sea ice in better agreement with observations. Changes to the aerosol and related cloud properties are the key drivers of the improved GMST simulation despite only a modest change in aerosol ERF (+0.08 Wm-2). The total anthropogenic ERF increases from 1.76 Wm-2 in UKESM1 to 1.84 Wm-2 in UKESM1.1. The effective climate sensitivity (5.27 K) and transient climate response (2.64 K) remain largely unchanged from UKESM1 (5.36 K and 2.76 K respectively).

Jane Patricia Mulcahy et al.

Status: final response (author comments only)

Comment types: AC – author | RC – referee | CC – community | EC – editor | CEC – chief editor | : Report abuse
  • RC1: 'Comment on gmd-2022-113', Andrew Gettelman, 24 Sep 2022
    • AC1: 'Reply on RC1', Jane Mulcahy, 16 Jan 2023
  • RC2: 'Comment on gmd-2022-113', Anonymous Referee #2, 04 Oct 2022
    • AC2: 'Reply on RC2', Jane Mulcahy, 16 Jan 2023
    • AC3: 'Reply to RC2 - Additional Supplement', Jane Mulcahy, 16 Jan 2023
  • AC3: 'Reply to RC2 - Additional Supplement', Jane Mulcahy, 16 Jan 2023

Jane Patricia Mulcahy et al.

Jane Patricia Mulcahy et al.


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Short summary
Recent global climate models simulate historical global mean surface temperatures which are colder than observed possibly to due to aerosol cooling. This raises questions about the model’s ability to simulate important climate processes and reduces confidence in their future climate predictions. We present a new version of the UK Earth System Model which has an improved simulation of aerosols and historical temperature record. Results from a range of climate change experiments are presented.