Decoding the dynamics of poleward shifting climate zones using aqua-planet model simulations

Journal Article · 05 January 2022 · Climate Dynamics

DOI: https://doi.org/10.1007/s00382-021-06112-0 · OSTI ID:1862685

Yang, Hu  ^[1]; Lu, Jian ^[2]; Wang, Qiang ^[1]; Shi, Xiaoxu ^[1]; Lohmann, Gerrit ^[1]

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1. Helmholtz Centre for Polar and Marine Research, Bremerhaven (Germany). Alfred Wegener Inst.
2. Pacific Northwest National Lab. (PNNL), Richland, WA (United States)

Growing evidence indicates that the atmospheric and oceanic circulation experiences a systematic poleward shift in a warming climate. However, the complexity of the climate system, including the coupling between the ocean and the atmosphere, natural climate variability and land-sea distribution, tends to obfuscate the causal mechanism underlying the circulation shift. Here, using an idealised coupled aqua-planet model, we explore the mechanism of the shifting circulation, by isolating the contributing factors from the direct CO₂ forcing, the indirect ocean surface warming, and the wind-stress feedback from the ocean dynamics. We find that, in contrast to the direct CO₂ forcing, ocean surface warming, in particular an enhanced subtropical ocean warming, plays an important role in driving the circulation shift. This enhanced subtropical ocean warming emerges from the background Ekman convergence of surface anomalous heat in the absence of the ocean dynamical change. Additionally, it expands the tropical warm water zone, causes a poleward shift of the mid-latitude temperature gradient, hence forces a corresponding shift in the atmospheric circulation and the associated wind pattern. The shift in wind, in turn drives a shift in the ocean circulation. Our simulations, despite being idealised, capture the main features of the observed climate changes, for example, the enhanced subtropical ocean warming, poleward shift of the patterns of near-surface wind, sea level pressure, storm tracks, precipitation and large-scale ocean circulation, implying that increase in greenhouse gas concentrations not only raises the temperature, but can also systematically shift the climate zones poleward.

• Research Organization: Pacific Northwest National Laboratory (PNNL), Richland, WA (United States)
• Sponsoring Organization: USDOE Office of Science (SC)
• Grant/Contract Number: AC05-76RL01830
• OSTI ID: 1862685
• Report Number(s): PNNL-SA-161120
• Journal Information: Climate Dynamics, Journal Name: Climate Dynamics Journal Issue: 11-12 Vol. 58; ISSN 0930-7575
• Publisher: Springer-VerlagCopyright Statement
• Country of Publication: United States
• Language: English