January 7, 2025
Journal Article

Roles of the Atmosphere and Ocean in the Projected North Atlantic Warming Hole

Abstract

There exists a warming deficit in sea surface temperatures (SST) over the subpolar North Atlantic in response to quadrupled CO2, referred to as the projected North Atlantic warming hole (WH). This study employs a partial coupling technique to accurately verify the relative roles of oceanic and atmospheric processes in the formation of the projected WH within an atmosphere-ocean coupled framework. By decomposing the anomalous SST in the subpolar North Atlantic into two components: those induced by atmospheric processes (i.e., the atmosphere-forced component) and those driven by changes in ocean circulation (i.e., the ocean-driven component), we find that the projected WH is primarily driven by changes in ocean circulation, with almost no contribution from atmospheric processes. Specifically, the slowdown of the Atlantic Meridional Overturning Circulation (AMOC) results in a cooling of SST in the WH region due to reduced northward ocean heat transport into this region. Furthermore, this study investigates and quantifies the influence of a positive coupled feedback on the AMOC response under greenhouse gas forcing within this self-consistent framework. We find that atmospheric forcing initially weakens the AMOC, resulting in a negative SST anomaly in the subpolar North Atlantic and subsequently leading to a positive ocean-driven surface heat flux anomaly, which in turn further weakens the AMOC. This positive feedback contributes about 50% to the overall AMOC slowdown in response to quadrupled CO2.

Published: January 7, 2025

Citation

Li Q., Y. Luo, J. Lu, F. Liu, and H. Teng. 2024. Roles of the Atmosphere and Ocean in the Projected North Atlantic Warming Hole. Climate Dynamics 62, no. 8:7465–7480. PNNL-SA-191413. doi:10.1007/s00382-024-07289-w