Northwestward Migration of the Northern Edge of the East Asian Summer Monsoon During the Mid‐Pliocene Warm Period: Simulations and Reconstructions

Abstract

The mid‐Pliocene (~3.3–3.0 Ma) was the most recent warm interval during which atmospheric CO2 concentrations were similar to the present level of ~400 ppmv. Therefore, it is often regarded as an analog for a near‐future climate scenario. To examine the behavior of the East Asian summer monsoon (EASM) during the mid‐Pliocene warm period, the northern edge of the EASM, a sensitive indicator of the advance and retreat of the summer monsoon rainbelt, was analyzed using the output of the Pliocene Model Intercomparison Project Phase 1. The results show a ~150‐km‐northwestward migration of the northern edge of the EASM during the mid‐Pliocene compared to the preindustrial period, which is consistent with that derived from a comparison of geological records and modern observations. However, the geological records indicate a greater east‐west climatic contrast during the Pliocene than at present, which requires investigation in future modeling studies. The simulations also show a substantial increase in the large‐scale land‐sea thermal contrast between the East Asian mainland and the equatorial western Pacific during the interval of mid‐Pliocene warmth. This led to the intensification and westward extension of the western Pacific subtropical high, causing a northwestward shift of the EASM and the resulting mitigation of drought in northern China. We suggest that global warming will shift the EASM northwestward mainly via changes in the position and intensity of the western Pacific subtropical high; this requires systematic studies in the future based on meteorological observations and simulations.

Sensitivity of Water Balance in the Qaidam Basin to the Mid‐Pliocene Climate

“…The changes in large-scale circulation patterns in PLIO are in good agreement with recent modeling studies (Huang et al, 2019;X. Li et al, 2015;Zhang et al, 2013).…”

“…S2. 1b) component of the subtropical EASM and regulates the northern edge of the EASM (Huang et al, 2019). The strengthening of the EASM in PLIO is coupled with a tilted jet stream axis over northeastern China.…”

Temperature Control on Silicate Weathering Intensity and Evolution of the Neogene East Asian Summer Monsoon

“…4–9 ka), both precipitation and circulation were controlled by monsoons (Cheng et al, 2012; T. Liu & Ding, 1998; Tian et al, 2001; Winkler & Wang, 1993), indicating that this site is sensitive to the inland migration of monsoon precipitation over 10 3 –10 6 year timescales. Atmosphere general circulation models and coupled atmosphere‐ocean general circulation models indicate that the East Asian summer monsoon penetrated further inland during the Pliocene warm period and the Qaidam Basin is within the monsoon precipitation region (Huang et al, 2019), confirming Qaidam Basin's sensitivity to monsoon precipitation boundary migration.…”

Anti‐Phase Strengthening of the South and East Asian Summer Monsoons During the Early Pliocene Driven by Southern Hemisphere Ice Volume

“…This inconsistency between Northern Hemisphere high latitude sea surface temperatures and global ice volume record suggests that ice sheet size variations mostly occurred in Antarctica. Although some recent model simulations suggest that East Asian summer monsoon would intensify with larger Antarctica ice sheets (Ao et al, 2016;Shi et al, 2020), model simulations of the Pliocene Asian summer monsoon yield variable, often conflicting, results suggesting that more research is needed to resolve these inconsistencies (An et al, 2001;Ao et al, 2016;X. Huang et al, 2019;Yan et al, 2018).…”

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Asian monsoon variations and forcing mechanisms in geological warm periods are instructive to understanding future evolution with a warmer-than-present climate driven by anthropogenic climate change (X. Huang et al, 2019). The Pliocene epoch is a potential analog for future climate under increased CO 2 concentrations (Fedorov et al, 2006;Haywood & Valdes, 2004), but mechanisms responsible for Pliocene Asian monsoon variations are not entirely clear (cf.

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