29 Aug 2022
29 Aug 2022

The response of hemispheric differences in Earth’s albedo to CO2 forcing in coupled models and its implications for shortwave radiative feedback strength

Aiden R. Jönsson1,2 and Frida A.-M. Bender1,2 Aiden R. Jönsson and Frida A.-M. Bender
  • 1Department of Meteorology, Stockholm University
  • 2Bolin Centre for Climate Research

Abstract. The Earth’s albedo is observed to be symmetric between the hemispheres on the annual mean timescale, despite the clear-sky albedo being asymmetrically higher in the northern hemisphere due to more land area and aerosol sources; this is because the mean cloud distribution currently compensates for the clear-sky asymmetry almost exactly. We investigate the evolution of the hemispheric difference in albedo in CMIP6 coupled model simulations following an abrupt quadrupling of CO2 concentrations, to which all models respond with an initial decrease of albedo in the northern hemisphere (NH) due to loss of Arctic sea ice. After this initial NH darkening, the evolution of the hemispheric albedo difference diverges among models, with some models remaining at their new hemispheric albedo difference, and others returning towards their pre-industrial difference through either a reduction in SH clouds or an increase in NH clouds, or a combination of the two. These responses have different implications on the reduction in global albedo, and thereby the strength of the shortwave cloud feedback: if a cross-hemispheric communicating mechanism is primarily responsible for maintaining hemispheric albedo symmetry, the total shortwave radiative feedback must be more strongly positive. We also show that in these models, there is a link between the extent of reductions in SH extratropical cloud cover and Antarctic albedo decline due to increased poleward heat transport in the SH.

Aiden R. Jönsson and Frida A.-M. Bender

Status: final response (author comments only)

Comment types: AC – author | RC – referee | CC – community | EC – editor | CEC – chief editor | : Report abuse
  • RC1: 'Comment on egusphere-2022-811', Anonymous Referee #1, 04 Oct 2022
    • AC1: 'Reply on RC1', Aiden Jönsson, 20 Dec 2022
  • RC2: 'Comment on egusphere-2022-811', Anonymous Referee #2, 20 Oct 2022
    • AC2: 'Reply on RC2', Aiden Jönsson, 20 Dec 2022

Aiden R. Jönsson and Frida A.-M. Bender

Aiden R. Jönsson and Frida A.-M. Bender


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Short summary
The Earth has nearly the same mean albedo in both hemispheres, a feature not well replicated by climate models. Global warming causes changes in surface and cloud properties that affect albedo, in turn feeding back into the warming. We show that models predict more darkening due to ice loss in the northern than the southern hemisphere in response to increasing CO2 concentrations. This is to varying degrees counteracted by changes in cloud cover, with implications for cloud feedback on climate.