Persistent Climate Model Biases in the Atlantic Ocean's Freshwater Transport

The Atlantic Meridional Overturning Circulation (AMOC) is considered to be one of the most dangerous climate tipping elements. The salt–advection feedback plays an important role in AMOC tipping behaviour, and its strength is strongly connected to the freshwater transport carried by the AMOC at 34°...

Full description

Bibliographic Details
Main Authors: Westen, René M., Dijkstra, Henk A.
Format: Text
Language:English
Published: 2024
Subjects:
Online Access:https://doi.org/10.5194/egusphere-2023-1502
https://egusphere.copernicus.org/preprints/2023/egusphere-2023-1502/
id ftcopernicus:oai:publications.copernicus.org:egusphere113008
record_format openpolar
spelling ftcopernicus:oai:publications.copernicus.org:egusphere113008 2024-06-23T07:54:51+00:00 Persistent Climate Model Biases in the Atlantic Ocean's Freshwater Transport Westen, René M. Dijkstra, Henk A. 2024-04-12 application/pdf https://doi.org/10.5194/egusphere-2023-1502 https://egusphere.copernicus.org/preprints/2023/egusphere-2023-1502/ eng eng doi:10.5194/egusphere-2023-1502 https://egusphere.copernicus.org/preprints/2023/egusphere-2023-1502/ eISSN: Text 2024 ftcopernicus https://doi.org/10.5194/egusphere-2023-1502 2024-06-13T01:23:50Z The Atlantic Meridional Overturning Circulation (AMOC) is considered to be one of the most dangerous climate tipping elements. The salt–advection feedback plays an important role in AMOC tipping behaviour, and its strength is strongly connected to the freshwater transport carried by the AMOC at 34° S, below indicated by F ovS . Available observations have indicated that F ovS has a negative sign for the present-day AMOC. However, most climate models of the Coupled Model Intercomparison Project (CMIP, phase 3 and phase 5) have an incorrect F ovS sign. Here, we analyse a high-resolution and a low-resolution version of the Community Earth System Model (CESM) to identify the origin of these F ovS biases. Both CESM versions are initialised from an observed ocean state, and F ovS biases quickly develop under fixed pre-industrial forcing conditions. The most important model bias is a too fresh Atlantic Surface Water, which arises from deficiencies in the surface freshwater flux over the Indian Ocean. The second largest bias is a too saline North Atlantic Deep Water and arises through deficiencies in the freshwater flux over the Atlantic Subpolar Gyre region. Climate change scenarios branched from the pre-industrial simulations have an incorrect F ovS upon initialisation. Most CMIP phase 6 models have similar biases to those in the CESM. Due to the biases, the value of F ovS is not in agreement with available observations, and the strength of the salt advection feedback is underestimated. Values of F ovS are projected to decrease under climate change, and their response is also dependent on the various model biases. To better project future AMOC behaviour, an urgent effort is needed to reduce biases in the atmospheric components of current climate models. Text North Atlantic Deep Water North Atlantic Copernicus Publications: E-Journals Indian
institution Open Polar
collection Copernicus Publications: E-Journals
op_collection_id ftcopernicus
language English
description The Atlantic Meridional Overturning Circulation (AMOC) is considered to be one of the most dangerous climate tipping elements. The salt–advection feedback plays an important role in AMOC tipping behaviour, and its strength is strongly connected to the freshwater transport carried by the AMOC at 34° S, below indicated by F ovS . Available observations have indicated that F ovS has a negative sign for the present-day AMOC. However, most climate models of the Coupled Model Intercomparison Project (CMIP, phase 3 and phase 5) have an incorrect F ovS sign. Here, we analyse a high-resolution and a low-resolution version of the Community Earth System Model (CESM) to identify the origin of these F ovS biases. Both CESM versions are initialised from an observed ocean state, and F ovS biases quickly develop under fixed pre-industrial forcing conditions. The most important model bias is a too fresh Atlantic Surface Water, which arises from deficiencies in the surface freshwater flux over the Indian Ocean. The second largest bias is a too saline North Atlantic Deep Water and arises through deficiencies in the freshwater flux over the Atlantic Subpolar Gyre region. Climate change scenarios branched from the pre-industrial simulations have an incorrect F ovS upon initialisation. Most CMIP phase 6 models have similar biases to those in the CESM. Due to the biases, the value of F ovS is not in agreement with available observations, and the strength of the salt advection feedback is underestimated. Values of F ovS are projected to decrease under climate change, and their response is also dependent on the various model biases. To better project future AMOC behaviour, an urgent effort is needed to reduce biases in the atmospheric components of current climate models.
format Text
author Westen, René M.
Dijkstra, Henk A.
spellingShingle Westen, René M.
Dijkstra, Henk A.
Persistent Climate Model Biases in the Atlantic Ocean's Freshwater Transport
author_facet Westen, René M.
Dijkstra, Henk A.
author_sort Westen, René M.
title Persistent Climate Model Biases in the Atlantic Ocean's Freshwater Transport
title_short Persistent Climate Model Biases in the Atlantic Ocean's Freshwater Transport
title_full Persistent Climate Model Biases in the Atlantic Ocean's Freshwater Transport
title_fullStr Persistent Climate Model Biases in the Atlantic Ocean's Freshwater Transport
title_full_unstemmed Persistent Climate Model Biases in the Atlantic Ocean's Freshwater Transport
title_sort persistent climate model biases in the atlantic ocean's freshwater transport
publishDate 2024
url https://doi.org/10.5194/egusphere-2023-1502
https://egusphere.copernicus.org/preprints/2023/egusphere-2023-1502/
geographic Indian
geographic_facet Indian
genre North Atlantic Deep Water
North Atlantic
genre_facet North Atlantic Deep Water
North Atlantic
op_source eISSN:
op_relation doi:10.5194/egusphere-2023-1502
https://egusphere.copernicus.org/preprints/2023/egusphere-2023-1502/
op_doi https://doi.org/10.5194/egusphere-2023-1502
_version_ 1802647151406219264