Transient and Equilibrium Responses of the Atlantic Overturning Circulation to Warming in Coupled Climate Models: The Role of Temperature and Salinity

The long-term response of the Atlantic meridional overturning circulation (AMOC) to climate change remains poorly understood, in part due to the computational expense associated with running atmosphere–ocean general circulation models (GCMs) to equilibrium. Here, we use a collection of millennial-le...

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Published in:Journal of Climate
Main Authors: Bonan, David B., Thompson, Andrew F., Newsom, Emily R., Sun, Shantong, Rugenstein, Maria
Format: Article in Journal/Newspaper
Language:unknown
Published: American Meteorological Society 2022
Subjects:
Online Access:https://authors.library.caltech.edu/116124/
https://resolver.caltech.edu/CaltechAUTHORS:20220804-250049000
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spelling ftcaltechauth:oai:authors.library.caltech.edu:116124 2023-05-15T15:12:55+02:00 Transient and Equilibrium Responses of the Atlantic Overturning Circulation to Warming in Coupled Climate Models: The Role of Temperature and Salinity Bonan, David B. Thompson, Andrew F. Newsom, Emily R. Sun, Shantong Rugenstein, Maria 2022-08-01 https://authors.library.caltech.edu/116124/ https://resolver.caltech.edu/CaltechAUTHORS:20220804-250049000 unknown American Meteorological Society Bonan, David B. and Thompson, Andrew F. and Newsom, Emily R. and Sun, Shantong and Rugenstein, Maria (2022) Transient and Equilibrium Responses of the Atlantic Overturning Circulation to Warming in Coupled Climate Models: The Role of Temperature and Salinity. Journal of Climate, 35 (15). pp. 5173-5193. ISSN 0894-8755. doi:10.1175/jcli-d-21-0912.1. https://resolver.caltech.edu/CaltechAUTHORS:20220804-250049000 <https://resolver.caltech.edu/CaltechAUTHORS:20220804-250049000> Article PeerReviewed 2022 ftcaltechauth https://doi.org/10.1175/jcli-d-21-0912.1 2022-08-11T17:54:37Z The long-term response of the Atlantic meridional overturning circulation (AMOC) to climate change remains poorly understood, in part due to the computational expense associated with running atmosphere–ocean general circulation models (GCMs) to equilibrium. Here, we use a collection of millennial-length GCM simulations to examine the transient and equilibrium responses of the AMOC to an abrupt quadrupling of atmospheric carbon dioxide. We find that GCMs consistently simulate an AMOC weakening during the first century but exhibit diverse behaviors over longer time scales, showing different recovery levels. To explain the AMOC behavior, we use a thermal-wind expression, which links the overturning circulation to the meridional density difference between deep-water formation regions and the Atlantic basin. Using this expression, we attribute the evolution of the AMOC on different time scales to changes in temperature and salinity in distinct regions. The initial AMOC shoaling and weakening occurs on centennial time scales and is attributed to a warming of the deep-water formation region. A partial recovery of the AMOC occurs over the next few centuries, and is linked to a simultaneous warming of the Atlantic basin and a positive high-latitude salinity anomaly. The latter reduces the subsurface stratification and reinvigorates deep-water formation. GCMs that exhibit a prolonged AMOC weakening tend to have smaller high-latitude salinity anomalies and increased Arctic sea ice loss. After multiple millennia, the AMOC in some GCMs is stronger than the initial state due to warming of the low-latitude Atlantic. These results highlight the importance of considering high-latitude freshwater changes when examining the past and future evolution of the AMOC evolution on long time scales. Article in Journal/Newspaper Arctic Climate change Sea ice Caltech Authors (California Institute of Technology) Arctic Journal of Climate 35 15 5173 5193
institution Open Polar
collection Caltech Authors (California Institute of Technology)
op_collection_id ftcaltechauth
language unknown
description The long-term response of the Atlantic meridional overturning circulation (AMOC) to climate change remains poorly understood, in part due to the computational expense associated with running atmosphere–ocean general circulation models (GCMs) to equilibrium. Here, we use a collection of millennial-length GCM simulations to examine the transient and equilibrium responses of the AMOC to an abrupt quadrupling of atmospheric carbon dioxide. We find that GCMs consistently simulate an AMOC weakening during the first century but exhibit diverse behaviors over longer time scales, showing different recovery levels. To explain the AMOC behavior, we use a thermal-wind expression, which links the overturning circulation to the meridional density difference between deep-water formation regions and the Atlantic basin. Using this expression, we attribute the evolution of the AMOC on different time scales to changes in temperature and salinity in distinct regions. The initial AMOC shoaling and weakening occurs on centennial time scales and is attributed to a warming of the deep-water formation region. A partial recovery of the AMOC occurs over the next few centuries, and is linked to a simultaneous warming of the Atlantic basin and a positive high-latitude salinity anomaly. The latter reduces the subsurface stratification and reinvigorates deep-water formation. GCMs that exhibit a prolonged AMOC weakening tend to have smaller high-latitude salinity anomalies and increased Arctic sea ice loss. After multiple millennia, the AMOC in some GCMs is stronger than the initial state due to warming of the low-latitude Atlantic. These results highlight the importance of considering high-latitude freshwater changes when examining the past and future evolution of the AMOC evolution on long time scales.
format Article in Journal/Newspaper
author Bonan, David B.
Thompson, Andrew F.
Newsom, Emily R.
Sun, Shantong
Rugenstein, Maria
spellingShingle Bonan, David B.
Thompson, Andrew F.
Newsom, Emily R.
Sun, Shantong
Rugenstein, Maria
Transient and Equilibrium Responses of the Atlantic Overturning Circulation to Warming in Coupled Climate Models: The Role of Temperature and Salinity
author_facet Bonan, David B.
Thompson, Andrew F.
Newsom, Emily R.
Sun, Shantong
Rugenstein, Maria
author_sort Bonan, David B.
title Transient and Equilibrium Responses of the Atlantic Overturning Circulation to Warming in Coupled Climate Models: The Role of Temperature and Salinity
title_short Transient and Equilibrium Responses of the Atlantic Overturning Circulation to Warming in Coupled Climate Models: The Role of Temperature and Salinity
title_full Transient and Equilibrium Responses of the Atlantic Overturning Circulation to Warming in Coupled Climate Models: The Role of Temperature and Salinity
title_fullStr Transient and Equilibrium Responses of the Atlantic Overturning Circulation to Warming in Coupled Climate Models: The Role of Temperature and Salinity
title_full_unstemmed Transient and Equilibrium Responses of the Atlantic Overturning Circulation to Warming in Coupled Climate Models: The Role of Temperature and Salinity
title_sort transient and equilibrium responses of the atlantic overturning circulation to warming in coupled climate models: the role of temperature and salinity
publisher American Meteorological Society
publishDate 2022
url https://authors.library.caltech.edu/116124/
https://resolver.caltech.edu/CaltechAUTHORS:20220804-250049000
geographic Arctic
geographic_facet Arctic
genre Arctic
Climate change
Sea ice
genre_facet Arctic
Climate change
Sea ice
op_relation Bonan, David B. and Thompson, Andrew F. and Newsom, Emily R. and Sun, Shantong and Rugenstein, Maria (2022) Transient and Equilibrium Responses of the Atlantic Overturning Circulation to Warming in Coupled Climate Models: The Role of Temperature and Salinity. Journal of Climate, 35 (15). pp. 5173-5193. ISSN 0894-8755. doi:10.1175/jcli-d-21-0912.1. https://resolver.caltech.edu/CaltechAUTHORS:20220804-250049000 <https://resolver.caltech.edu/CaltechAUTHORS:20220804-250049000>
op_doi https://doi.org/10.1175/jcli-d-21-0912.1
container_title Journal of Climate
container_volume 35
container_issue 15
container_start_page 5173
op_container_end_page 5193
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