Aerosol Forcing Masks and Delays the Formation of the North Atlantic Warming Hole by Three Decades.

Guy Dagan,Duncan Watson-Parris,Philip Stier

doi:10.1029/2020gl090778

Abstract

The North Atlantic warming hole (NAWH) is referred to as a reduced warming, or even cooling, of the North Atlantic during an anthropogenic‐driven global warming. A NAWH is predicted by climate models during the 21st century, and its pattern is already emerging in observations. Despite the known key role of the North Atlantic surface temperatures in setting the Northern Hemisphere climate, the mechanisms behind the NAWH are still not fully understood. Using state‐of‐the‐art climate models, we show that anthropogenic aerosol forcing opposes the formation of the NAWH (by leading to a local warming) and delays its emergence by about 30 years. In agreement with previous studies, we also demonstrate that the relative warming of the North Atlantic under aerosol forcing is due to changes in ocean heat fluxes, rather than air‐sea fluxes. These results suggest that the predicted reduction in aerosol forcing during the 21st century may accelerate the formation of the NAWH.

Highlights

The North Atlantic surface temperature plays a key role in the Northern Hemisphere's climate (O'Reilly et al, 2017; Woollings et al, 2012; Zhang & Delworth, 2006)
While climate models predict a global increase in temperature due to anthropogenic emissions of greenhouse gases (GHGs), the surface temperature in the North Atlantic is predicted to decrease due to changes in the ocean meridional heat flux (Caesar et al, 2018; Chemke et al, 2020; Cheng et al, 2013; Drijfhout et al, 2012; Gervais et al, 2018; Manabe & Stouffer, 1993; Marshall et al, 2015; Menary & Wood, 2018; Piecuch et al, 2017; Rahmstorf et al, 2015; Robson et al, 2016; Woollings et al, 2012)
We start by examining the surface temperature change in CMIP6 hist‐aer simulations compared to the preindustrial control runs

Summary

Introduction

The North Atlantic surface temperature plays a key role in the Northern Hemisphere's climate (O'Reilly et al, 2017; Woollings et al, 2012; Zhang & Delworth, 2006). While climate models predict a global increase in temperature due to anthropogenic emissions of greenhouse gases (GHGs), the surface temperature in the North Atlantic is predicted to decrease due to changes in the ocean meridional heat flux (Caesar et al, 2018; Chemke et al, 2020; Cheng et al, 2013; Drijfhout et al, 2012; Gervais et al, 2018; Manabe & Stouffer, 1993; Marshall et al, 2015; Menary & Wood, 2018; Piecuch et al, 2017; Rahmstorf et al, 2015; Robson et al, 2016; Woollings et al, 2012). Unlike GHGs, aerosols are inhomogeneously distributed in the atmosphere and are generally assumed to drive corresponding regional changes to the atmospheric circulation

Methods

Results

Conclusion