The Role of a Weakened Atlantic Meridional Overturning Circulation in Modulating Marine Heatwaves in a Warming Climate

• Published in: Geophysical research letters Vol. 48; no. 23
• Main Authors: Ren, Xianglin, Liu, Wei
• Format: Journal Article
• Language: English
• Published: 16.12.2021
• ISSN: 0094-8276; 1944-8007
• DOI: 10.1029/2021GL095941

We explore the effect of Atlantic meridional overturning circulation (AMOC) slowdown on global marine heatwaves (MHWs) under anthropogenic warming by maintaining AMOC strength in climate model simulations throughout the 21st century. The AMOC slowdown has an insignificant effect on global MHWs during the past four decades, except those over the North Atlantic warming hole (NAWH) where the weakened AMOC reduces the occurrence and duration of MHWs by about half by creating a cooler mean‐state sea surface temperature. As the AMOC continues weakening in current century, its effect becomes significant on MHWs in the North Atlantic and Pacific Oceans. The weakened AMOC induces a bipolar‐seesaw‐like change in MHW frequencies, with more frequent MHWs in the Southern Hemisphere but less frequent MHWs in the North Hemisphere except over the NAWH. The reason for the exception is that the NAWH region would enter a near‐permanent MHW state without an AMOC slowdown. Plain Language Summary In this study, we examine how the weakened Atlantic meridional overturning circulation (AMOC) affects global MHWs under greenhouse gas warming. We conduct a climate model experiment by keeping AMOC magnitude constant throughout the 21st century and compare this experiment with a parallel AMOC weakening case. We find that the AMOC effect on MHWs is insignificant over most of global oceans during the past four decades. The only exception happens to a region to the south of Greenland that is so‐called the North Atlantic warming hole (NAWH). The weakened AMOC creates a cooler mean‐state sea surface temperature in this region than the others, which helps reduce the occurrence and duration of MHWs there. Since the magnitude of AMOC weakening is expected to be larger as time goes on, the AMOC effect on MHWs will become significant later in the 21st century, especially in the North Atlantic and North Pacific. The weakened AMOC will make MHWs more frequent in the Southern Hemisphere but less frequent in the North Hemisphere except in the NAWH region. The reason for the exception is that, if the AMOC were not to slow down, MHWs would occur in the NAWH region almost all year round. Key Points The AMOC slowdown has an insignificant effect on global MHWs over the past four decades except those at the NAWH The effect of the AMOC on MHWs will become significant in broad areas in the North Atlantic and North Pacific by the end of current century The NAWH region would reach a near‐permanent MHW state over 2061–2100 without a slowdown of the AMOC