Journal Article

Constraints on the Projected Tropical Pacific Sea Surface Temperature Warming Pattern by the Tropical North Atlantic Cold SST Bias in CMIP6 Models

Ying, Jun, Chadwick, Robin, Lian, Tao, Ma, Jian, Collins, Matthew

2024

Overview

Reliable projections of the tropical Pacific sea surface temperature (SST) warming (TPSW) patterns are critically important for exploring the future climate change. However, climate models suffer from long‐standing common biases in simulating the present‐day climate, raising doubts about the model projected TPSW patterns. Here by using outputs from 30 CMIP6 models, we find the projected TPSW patterns are significantly correlated with the simulated present‐day SST in the tropical North Atlantic (TNA), with higher present‐day TNA SSTs tending to project more weakened zonal SST gradients by producing more present‐day low‐level clouds and the resultant positive cloud–shortwave–SST feedbacks over the eastern equatorial Pacific. An emergent constraint using observed TNA SST reveals a consistent El Niño‐like warming pattern in all models with more weakened zonal SST gradient than before in most models, together with a reduction of the inter‐model uncertainty in the zonal SST gradient change by more than 20%. Plain Language Summary Future projections of the tropical Pacific SST warming (TPSW) pattern remain highly uncertain. One of the key reasons is that climate models suffer from several long‐standing common biases in simulating the current climate state. Here we find that the remote common cold SST bias in the tropical North Atlantic acts to suppress the future SST warming over the eastern equatorial Pacific through a trans‐basin atmospheric connection. By removing the effect of the TNA cold SST bias from model projections, the corrected TPSW displays a more El Niño‐like SST warming pattern with more weakened zonal SST gradient, together with a reduction of the inter‐model uncertainty by more than 20%. Key Points Models with a higher (lower) present‐day tropical North Atlantic (TNA) sea surface temperature (SST) tend to project a more (less) El Niño‐like SST warming pattern The TNA cold SST bias leads to a lack of low‐level cloud over the eastern Pacific by weakening the regional Hadley‐type circulation Spatial constraints on the projected tropical Pacific SST warming from the observed TNA SST suggest a more El Niño‐like warming pattern

• Publisher: John Wiley & Sons, Inc,Wiley
• Subject: Atmospheric correction / Bias / Climate change / Climate models / Common cold / Constraints / El Nino / El Nino phenomena / Future climates / model bias / Sea surface temperature / spatial emergent constraint / tropical Pacific SST warming pattern / Uncertainty