Aerosol-forced AMOC changes in CMIP6 historical simulations.

Matthew Menary,Juliette Mignot,Rowan Sutton,Dan Hodson,Ben Booth,Richard Allan,Mark Ringer,Jonathan Gregory,Laura Wilcox,Jon Robson,Colin Jones,Christophe Cassou,Guillaume Gastineau,Rong Zhang

doi:10.5194/egusphere-egu2020-2379

Abstract

&lt;p&gt;The Atlantic Meridional Overturning Circulation (AMOC) has been, and will continue to be, a key factor in the modulation of climate change both locally and globally. Reliable simulations of its decadal to century-timescale evolution are key to providing skilful predictions of future regional climate, and to understanding the likelihood of a potential AMOC collapse. However, there remains considerable uncertainty even in past AMOC evolution. Here, we show that the multi-model mean AMOC strengthened by approximately 10% to 1985 in new historical simulations for the 6th Coupled Model Inter-comparison Project (CMIP6), contrary to results obtained from CMIP5. The simulated strengthening is due to a stronger anthropogenic aerosol forcing, in particular due to aerosol-cloud interactions. However, comparison with an observed sea surface temperature fingerprint of AMOC evolution during 1850-1985, and the shortwave forcing during 1985-2014, suggest that anthropogenic forcing and the subsequent AMOC response may be overestimated in some CMIP6 models.&lt;/p&gt;

Highlights

The Atlantic Meridional Overturning Circulation (AMOC) represents the Atlantic branch of the global overturning circulation
The multidecadal structure in Coupled Model Intercomparison Project Phase 5 (CMIP5) resembles that of Coupled Model Intercomparison Project 6 (CMIP6), but the strengthening toward the end of the 20th century is far less pronounced
In this paper we have shown that the multimodel mean AMOC in CMIP6 increases by ~10% from 1850 to the 1980s, in contrast to the CMIP5 multimodel mean, which shows little change over this time period

Summary

Introduction

The Atlantic Meridional Overturning Circulation (AMOC) represents the Atlantic branch of the global overturning circulation. Various lines of modeling and paleo‐oceanographic evidence suggest the AMOC may weaken under the effects of greenhouse gases (GHGs) (Gregory et al, 2005; Stommel, 1961; Stouffer et al, 2006; Thornalley et al, 2018; Wood et al, 1999), leading to consistent projections that the AMOC will weaken in the century (Collins et al, 2013). Such a weakening could have severe climate impacts (Jackson et al, 2015). In this study, we revisit the simulation of historical AMOC changes in the new CMIP6 simulations

Methods

Results

Conclusion