Pacific Warm Research Articles

Prediction of Summer Precipitation via Machine Learning with Key Climate Variables：A Case Study in Xinjiang, China

Study region: Xinjiang is located in the mid-latitude region of Eurasia in northwestern China. Precipitation is predominantly concentrated in northern Xinjiang, while southern Xinjiang remains comparatively arid. Summer precipitation accounts for 54.4% of the annual total. Study focus: This study aims to develop a machine learning model to predict summer precipitation (June–August) in XJ and explore the key variables contributing to summer precipitation in this region. The SHapley Additive exPlanations method was integrated with an extreme tree model to quantify the contributions of variables towards precipitation. Artificial neural networks, support vector machines, and extreme gradient boosting were considered to predict summer precipitation. To train the ML model, we used precipitation data from 1961 to 2012, whilst the forecast results from 2013 to 2017 were used for validation.New hydrological insights for the regions: The results demonstrated that the ANN model achieved robust performance during both the training and validation periods. For Northern and Southern XJ, the Mean Absolute Error and Root Mean Square Error of the ANN model were 15.34 (20.40) and 23.21 (30.01), respectively. The SHAP analysis showed that in the context of Northern Xinjiang, the Niño B Sea Surface Temperature Anomaly, Western Pacific Subtropical High Intensity, Pacific Subtropical High Intensity, and Multivariate ENSO Index play crucial roles in the prediction of summer precipitation. In Southern Xinjiang, the South China Sea Subtropical High Intensity, South China Sea Subtropical High Area, Western Pacific Warm Pool Strength, and Atlantic multidecadal oscillation have emerged as key variables affecting summer precipitation forecasting.

Stronger Westerly Wind Bursts in a Warming Climate: The Effects of the Pacific Warming Pattern, the Madden–Julian Oscillation, and Tropical Cyclones

Abstract Westerly wind bursts (WWBs) in the western–central equatorial Pacific are critical in El Niño–Southern Oscillation (ENSO) dynamics. Understanding how they may change with global warming has important implications for future projections of El Niño. In this study, we investigate how the enhanced eastern equatorial Pacific warming pattern, emerging in future climate projections, can influence WWB characteristics in an atmospheric general circulation model, CAM6. Changes in three main factors affecting WWBs—El Niño-conditions mean westerly wind stress anomalies, the Madden–Julian oscillation (MJO), and tropical cyclones (TCs)—are analyzed. We find that during El Niño onset (December–April), the WWB wind stress intensity remains largely unchanged but WWBs shift westward by about 20° of longitude. In contrast, during El Niño development (May–November), the WWB intensity increases by 41% or 79% in two warming scenarios considered [shared socioeconomic pathways (SSP5-8.5) and SSP2-4.5, respectively], which is mainly caused by a higher frequency of TC occurrence in the central tropical Pacific within 15°N/S. Further, we find that westerly wind speed anomalies associated with El Niño and the MJO also increase during El Niño development. However, as trade winds weaken in the central-eastern equatorial Pacific, the mean strength of the resulting westerly wind stress anomalies does not change much, and no significant eastward shift of WWBs is observed. Thus, our atmospheric model simulations suggest a strong TC-driven increase in WWB wind stress anomalies during El Niño development and hence a more important role of TCs in WWB generation, which in a coupled system could lead to stronger ENSO events, enhanced TC–ENSO coupling, and even greater intensification of WWBs.

Assessing CMIP Models’ Ability to Detect Observed Surface Warming Signals Related to Climate Change

Abstract Assessing if CMIP models can detect observed climate change signals is crucial for evaluating their realism and strengthening confidence in future projections. These signals can only be compared once distinguishable from the background climate “noise.” Built for impact studies but not detection purpose, the time of emergence (ToE) estimates when this occurs using a fixed signal-to-noise ratio. To more accurately assess models’ ability to reproduce observed climate change signals, we introduce the time of detection (ToD), which employs a statistical significance test of the nonlinear trend, accounting for the time series length. ToD and ToE are computed for sea surface temperature (SST) and relative SST (RSST) across four observational and 69 CMIP5/6 historical and shared socioeconomic pathways 5–8.5 (SSP5–8.5) scenario datasets. ToD precedes ToE and is less sensitive to the chosen threshold. While already detectable in most of the tropics, SST warming in the equatorial Pacific is detectable in ∼90% of models but only one out of four observational datasets, due to a stronger modeled warming. Because RSST signals are weaker than SST signals, they do not emerge anywhere but are detectable in two regions. The enhanced warming in the western Indian Ocean, detected in ∼45% of models, is not robust in observations when excluding pre-1960 dubious data. Conversely, the subdued southeast Pacific warming detected in observations and ∼80% of models is robust and consistent with a poleward extension of the Southern Hemisphere Hadley cell. The ToD’s ability to detect subtle signals allows for assessing the realism of the CMIP warming pattern in this region. Significance Statement Recent studies emphasize the importance of the climate change warming pattern and its apparent discrepancy between climate models and observations in the equatorial Pacific. We argue that our newly proposed time of detection (ToD) is better suited than the well-known time of emergence (ToE) for investigating where modeled and observed warming patterns can be confidently compared. In agreement with previous studies, our analysis indicates model–observations disagreement over the equatorial Pacific. Using ToD instead of ToE allows for detecting a robust subdued warming (i.e., weaker than the tropical average) in the southeast Pacific and therefore confirms the realism of the CMIP warming pattern in this region.

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

AbstractReliable 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%.

Long-Term Teleconnections Between Global Circulation Patterns and Interannual Variability of Surface Air Temperature over Kingdom of Saudi Arabia

Surface air temperature (SAT) variability is investigated for advancing our understanding of the climate patterns over the Kingdom of Saudi Arabia (KSA). SAT variability reveals significant warming trends, particularly from 1994 onward, as demonstrated by nonlinear and linear trend analysis. This warming is linked to global climate patterns, which serve as significant indicators for studying the effects of climate change on surface air temperature patterns across the KSA. The empirical orthogonal function (EOF) method is employed for analyzing SAT due to its effectiveness in extracting dominant patterns of variability during the winter (DJF) and summer (JJA) seasons. The first mode (EOF1) for both seasons shows positive variability across the KSA, explaining more than 45% of the variance. The second mode (EOF2) indicates negative variability in central and northern regions. The third mode (EOF3) describes positive variability but with lower variance over time. PC1 is used to describe the physical mechanism of SAT variability and correlations with global sea surface temperature (SST). The physical mechanism shows that the variability in Mediterranean troughs during the winter season and high pressure over the Indian Ocean and central Asia controls SAT variability over the KSA. The correlation coefficients (CCs) were calculated during the winter and summer season between the SAT of the KSA and six teleconnection indices, El Niño Southern Oscillation (ENSO), Indian Ocean Dipole (IOD), Atlantic Meridional Mode (AMM), Pacific Warm Pool (PWP), North Atlantic Oscillation (NAO), and Tropical North Atlantic (TNA) SST for the period from 1994 to 2022. ENSO shifts from positive to negative correlations with SAT from winter to summer. IOD shows a diminished correlation with SAT due to the absence of upper air dynamics. PWP consistently enhances surface warming in both seasons through upper air convergence during both seasons. AMM and NAO have a non-significant impact on SAT; however, TNA contributes warming over central and northern parts during winter and summer seasons. The seasonal SAT variations emphasize the significant role of ENSO, PWP, and TNA across the seasons. The findings of this study can be helpful for seasonal predictability in the KSA.

Tropical Indian Ocean drives Hadley circulation change in a warming climate

Abstract The weakening and poleward expansion of the Hadley circulation (HC) are considered robust responses of atmospheric meridional circulation to anthropogenic warming. Climate impacts arising from these changes enhance drought conditions and reduce food production in the affected regions. Therefore, understanding the mechanisms of HC changes is critical to anticipating the resultant climate risks. First, we demonstrate that robust future HC changes in boreal winter, and the uncertainty in their future projections, are both largely related to sea surface temperature (SST) warming. Next, we investigate the impact of anthropogenic regional ocean warming on the future HC. Accordingly, we conduct a large ensemble of individual ocean basin perturbation experiments at 1.5 °C, 2 °C, and 3 °C warming thresholds (as in the Paris Agreement). These experiments highlight (i) the leading role of tropical Indian Ocean warming in HC changes and (ii) inter-model differences in tropical Pacific warming as a source of uncertainty in HC projections.

Differences in the impact of intense ENSO+ in Bahia Magdalena (SW of Baja California, Mexico) in the context of climate change

The Bahia Magdalena-Bahia Almejas (BM-BA) complex is the largest coastal lagoon system in the Mexican Pacific; it is in a transitional zone between temperate and tropical regions. BM-BA has a high biodiversity and is an important source of fishing resources; however, its productivity diminishes during ENSO+ events. This work aimed to compare the impact of the three most intense ENSOs (1982–1983, 1997–1998, and 2015–2016) on their environmental and biological characteristics in the context of global warming. Since 1970, this region has been warming, and the chlorophyll-a is diminishing; however, short-term environmental variations associated with basin-scale processes have modified these trends. The comparison showed that the equatorial influence on the 1997–1998 ENSO was more evident, while the North Pacific conditions and other large-scale environmental processes influenced the other ENSOs: in 1982–1983, the warm signal continued after the ENSO+ ended, and in 2015–2016, it was present before the ENSO+ onset due to the MWH The Blob and probably global warming. High temperatures at the basin scale altered large-scale wind patterns, weakening local upwelling and diminishing the nutrient input. The Equatorial and North Pacific influence on BM varies over time (as expected in a transition zone like BM); however, in recent years, North Pacific warming associated with climate change has probably gained relevance and modulated the effect of ENSO+.

The Relative Role of Indian and Pacific Tropical Heating as Seasonal Predictability Drivers for the North Atlantic Oscillation

AbstractUnderstanding the predictability drivers for the North Atlantic Oscillation (NAO) during boreal winter at seasonal time scales remains challenging. This study uses large ensembles with the ECMWF seasonal forecasting system to investigate the relative impact of tropical Indian and Pacific heating on NAO predictability by examining the tropical forcing, teleconnection pathways, and sources of uncertainty. We select three case studies ‐ 1997/98, 2015/16 and 2019/20 ‐ with strong Indian Ocean heating anomalies, but with different El Niño conditions. We show that in 2019/20, with neutral ENSO conditions, Indian Ocean SSTs favor a positive NAO response via stratospheric and tropospheric pathways. In the cases with strong El Niño, we find contrasting results: in 1997/98, the Pacific forcing dominates, producing a negative NAO. In 2015/16, despite the strong El Niño, the Indian Ocean forcing dominates, leading to a positive NAO via intensification of the stratospheric polar vortex (SPV). While the stratospheric pathway exhibits varying responses to Indian Ocean forcing ‐ being weaker in 1997/98 and strongest in 2015/16, the Indian Ocean‐related tropospheric pathway remains robust along the Pacific subtropical jet across years. However, there is destructive interference between teleconnections from Indian and Pacific SST anomalies in both the tropospheric and stratospheric pathways. The competing effects of tropical heating in both basins, uncertainties in the Rossby wave response to tropical heating and SPV variability contribute to uncertainty in seasonal NAO predictions. The flow‐dependent nature of the stratospheric pathway underscores the complexity of seasonal forecast predictability, and the existence of windows of opportunity.

Coupling is key for the tropical Indian and Atlantic oceans to boost super El Niño.

The influences of the tropical Indian and Atlantic oceans on the development of El Niño Southern Oscillation (ENSO), especially regarding super El Niño events, have been a subject of debate. In particular, several studies argue that these cross-basin influences may be mere statistical artifacts resulting from the high auto-correlation of ENSO. To clarify this issue, we conduct a series of perfect model hindcast experiments to untangle the individual and synergistic effects of the tropical Indian and Atlantic oceans. Our results clearly demonstrate that without these cross-basin effects, the Pacific warming would rarely reach super El Niño level. Specifically, the individual effect of the Indian Ocean efficiently enhances the development of super El Niño events. In contrast, the Atlantic's effect is initially limited because it fails to establish the Bjerknes feedback in the Pacific. However, when coupled with the Indian Ocean, the Atlantic's effect becomes more pronounced as it is amplified by the Bjerknes feedback established by the Indian Ocean.

Biennial variability of boreal spring surface air temperature over India

In this study, we report significant biennial variability or oscillation (BO) in the boreal spring (March–May) Surface Air Temperature (SAT) over India and unravelled the causative mechanisms. The positive phase of the BO exhibit significant seasonal warming over India, whereas seasonal cooling is observed during the negative phase of BO. Heat wave days are more during the positive phase of BO compared to negative or neutral phase. The positive (negative) phase of BO is generally coherent with the central (eastern) Pacific warming (cooling) years. The anomalous low-level divergence associated with low-level anticyclonic circulation induces less cloudiness and intense surface solar radiation ovr India during the positive phase, favouring surface warming. The evolution of some positive and/or negative phases of BO without any large scale forcing from the equatorial Pacific suggested the possibility of alternate pathways. The strong anomalous upper-level (at 200 hPa) anticyclonic circulation provoked by mid-latitude Rossby waves is found contributing to the positive phase, thereby highlighting the role of dominant mid-latitude pathways in the biennial SAT variability in addition to El Niño forcing. The sinking motion associated with persistent high, and the associated adiabatic compression also supported surface heating during the positive phase of BO. On the other hand, the mid-latitude Rossby wave induced upper-level cyclonic circulation is found contributing to the negative phase. The sinking motion associated with persistent high, and the associated adiabatic compression also supported surface heating during the positive phase of BO. In contrast, negative soil temperature anomalies and high latent heat flux release to the atmosphere supported surface cooling during the negative phase.

Vertical distribution of microplastics in the Western Pacific Warm Pool: In situ results comparison of different sampling method

Marine microplastics (MPs) are recognized as a growing severe environmental concern. The vertical distribution pattern of MPs in the ocean is still elusive. Meanwhile, different sampling methods have been deployed in previous studies, resulting in difficulties in compiling data. In this study, for the first time, we explored ocean interior MP pollution in the Western Pacific Warm Pool simultaneously using both a CTD (Conductivity-temperature-depth) sampler and a large-volume in-situ filtration system. At the same sampling station, the average abundance of microplastics in the water column obtained by the two sampling methods was 0.37 ± 0.44 n/m3 (in-situ filtration) and 115.12 ± 64.13 n/m3 (CTD), respectively, which showed significant differences. Both methods found that the main chemical composition and shape of MPs were PET and fiber. Ocean current was identified as the dominant factor that impacted the horizontal distribution of MPs in the study area. The abundance of MPs in the surface layer was 5.4–703.8 times higher than that of the water column. The similar physical and chemical properties of MPs in the surface water and water column indicated that MPs in the water column originate from the sustained release from the surface layer.

The vertical calcification mode of planktonic foraminifera in the Western Pacific Warm Pool

A thorough knowledge of the ecology of planktonic foraminifera throughout the water column is necessary for a reliable reconstruction of the paleooceanographic environment of the upper-middle water column. However, little is known about the planktonic foraminifera in the Western Pacific Warm Pool (WPWP), especially for the deep dwelling species. Here we present the stable oxygen isotope (δ18O) data of eight species collected from vertically stratified plankton tows across 0–500 m water depth from 5 sites in the WPWP during autumn, the vertical mode of foraminiferal calcification is explored. Vertical plankton tows provide more detailed information than other materials, it indicates a wider depth range of foraminiferal calcification than the other sample types. All the species exhibit a complex vertical calcification process that the majority of specimens precipitate their tests out of the depth at which they were obtained. It could be connected to the intricate hydrological conditions in the WPWP and/or the foraminiferal ontogenetic trajectory. Calcification depth range of the investigated species is substantially smaller than their living depth, and most of them prefer to calcify inside the abundant layers. Additionally, we found no clear correlation between foraminiferal test size and shell δ18O for any of the species that were studied at any of the locations.

Coral Sr/Ca-SST reconstruction from Fiji extending to ~1370 CE reveals insights into the Interdecadal Pacific Oscillation.

The southwestern tropical Pacific is a key center for the Interdecadal Pacific Oscillation (IPO), which regulates global climate. This study introduces a groundbreaking 627-year coral Sr/Ca sea surface temperature reconstruction from Fiji, representing the IPO's southwestern pole. Merging this record with other Fiji and central tropical Pacific records, we reconstruct the SST gradient between the southwestern and central Pacific (SWCP), providing a reliable proxy for IPO variability from 1370 to 1997. This reconstruction reveals distinct centennial-scale temperature trends and insights into Pacific-wide climate impacts and teleconnections. Notably, the 20th century conditions, marked by simultaneous basin-scale warming and weak tropical Pacific zonal-meridional gradients, deviate from trends observed during the past six centuries. Combined with model simulations, our findings reveal that a weak SWCP gradient most markedly affects IPO-related rainfall patterns in the equatorial Pacific. Persistent synchronous western and central Pacific warming rates could lead to further drying climate across the Coral Sea region, adversely affecting Pacific Island nations.

Long-term changes in the Western Pacific Warm Pool upper-water structure over the last 4 Ma

Earth's climate underwent secular structural evolution and cooling since the Pliocene Warmth, punctuated by increasing thermal gradients between the Western Pacific Warm Pool (WPWP) and the surrounding cooler regions of Eastern Pacific Cold Tongue and extra-tropics. One key mechanism for deciphering the climate evolution since Pliocene is the shoaling of the ocean thermocline, but much remains unknown about the upper-water structure of the western Pacific Warm Pool, the heat engine of the climate system, and its linkage to global ocean circulations. Here, by a newly made series of millennial-resolved δ18O and δ13C records of paired mixed-layer and thermocline dwelling planktonic foraminifera from IODP Site U1489 drilled in the center of WPWP, the trends of cooling and respired carbon content decreasing in the WPWP thermocline since ∼4 Ma are revisited and diagnosed. Our data allows us to propose that, the tropical Pacific upper-water circulation cell had shoaled and shrunk and the vertical mixing from deeper waters may have increased, since the Pliocene. Development towards a modern-style Warm Pool was initially onset at ∼3.1 and finalized at ∼0.7 Ma, respectively.

Processes that Contribute to Future South Asian Monsoon Differences in E3SMv2 and CESM2

AbstractTwo Earth system models are analyzed to gain insight into the processes that govern projected changes in the South Asian monsoon. Warmer present‐day base state tropical SSTs contribute to coupled processes that produce greater future tropical Pacific warming in CESM2 with less of an increase in season‐mean monsoon precipitation compared to E3SMv2. This is attributed to changes in the large‐scale east‐west atmospheric Walker circulation, with relatively larger increases in precipitation and upper‐level divergence over the tropical Pacific and increases in upper‐level convergence over South Asia in CESM2. The stronger El Niño‐like response in CESM2, which increases Pacific precipitation and upper‐level divergence farther to the east, and larger future ENSO amplitude in E3SMv2, produce a greater relative increase in future monsoon‐ENSO connections in E3SMv2 compared to CESM2. This analysis indicates that the key processes that affect future monsoon‐ENSO connections are ENSO amplitude and size of the future tropical Pacific El Niño‐like response.

Crucial role of sea surface temperature warming patterns in near-term high-impact weather and climate projection

Recent studies indicate that virtually all global climate models (GCMs) have had difficulty simulating sea surface temperature (SST) trend patterns over the past four decades. GCMs produce enhanced warming in the eastern Equatorial Pacific (EPAC) and Southern Ocean (SO) warming, while observations show intensified warming in the Indo-Pacific Warm Pool (IPWP) and slight cooling in the eastern EPAC and SO. Using Geophysical Fluid Dynamics Laboratory’s latest higher resolution atmospheric model and coupled prediction system, we show the model biases in SST trend pattern have profound implications for near-term projections of high-impact storm statistics, including the frequency of atmospheric rivers (AR), tropical storms (TS) and mesoscale convection systems (MCS), as well as for hydrological and climate sensitivity. If the future SST warming pattern continues to resemble the observed pattern from the past few decades rather than the GCM simulated/predicted patterns, our results suggest (1) a drastically different future projection of high-impact storms and their associated hydroclimate changes, especially over the Western Hemisphere, (2) a stronger global hydrological sensitivity, and (3) substantially less global warming due to stronger negative feedback and lower climate sensitivity. The roles of SST trend patterns over the EPAC, IPWP, SO, and the North Atlantic tropical cyclone Main Development Region (AMDR) are isolated, quantified, and used to understand the simulated differences. Specifically, SST trend patterns in the EPAC and AMDR are crucial for modeled differences in AR and MCS frequency, while those in the IPWP and AMDR are essential for differences in TS frequency over the North Atlantic.

Possible shift in controls of the tropical Pacific surface warming pattern.

Changes in the sea surface temperature (SST) pattern in the tropical Pacific modulate radiative feedbacks to greenhouse gas forcing, the pace of global warming and regional climate impacts. Therefore, elucidating the drivers of the pattern is critically important for reducing uncertainties in future projections. However, the causes of observed changes over recent decades, an enhancement of the zonal SST contrast coupled with a strengthening of the Walker circulation, are still debated. Here we focus on the role of external forcing and review existing mechanisms of the forced response categorized as either an energy perspective that adopts global and hemispheric energy budget constraints or a dynamical perspective that examines the atmosphere-ocean coupled processes. We then discuss their collective andrelative contributions to the past and future SST pattern changes and propose a narrative that reconciles them. Although definitive evidence is not yet available, our assessment suggests that the zonal SST contrast has been dominated by strengthening mechanisms in the past, but will shift towards being dominated byweakening mechanisms in the future. Finally, we present opportunities to resolve the model-observations discrepancy regarding the recent trends.

Competing impacts of tropical Pacific and Atlantic on Southern Ocean inter-decadal variability

The observed Southern Ocean sea surface temperature (SST) has experienced prominent inter-decadal variability nearly in phase with the Inter-decadal Pacific Oscillation (IPO), but less associated with the Atlantic Multidecadal Variability (AMV), challenging the prevailing view of Pacific-Atlantic synergistic effects. Yet, the mechanisms of distinct trans-hemispheric connections to the Southern Ocean remain indecisive. Here, by individually constraining the observed cold-polarity and warm-polarity IPO and AMV SSTs in a climate model, we show that the IPO is influential in initiating a basin-wide Southern Ocean response, with the AMV secondary. A tropical Pacific-wide cooling triggers a basin-scale Southern Ocean cold episode through a strong Rossby wave response to the north-to-south cross-equatorial weakened Hadley circulation. By contrast, due to the competing role of tropical Pacific cooling, an Atlantic warming partly cools the Southern Ocean via a weak Rossby wave response to the south-to-north cross-equatorial enhanced Hadley circulation. Conversely, tropical Pacific warming leads to a warm Southern Ocean episode. Our findings highlight that properly accounting for the tropical Pacific SST variability may provide a potential for skillful prediction of Southern Ocean climate change and more reliable estimates of climate sensitivity, currently overestimated by the misrepresented Southern Ocean warming.

Late Pleistocene island weathering and precipitation in the Western Pacific Warm Pool

Deciphering past climate variability in the Western Pacific Warm Pool (WPWP), the Earth’s largest heat and moisture centre, is vital for understanding the global climate system. Nevertheless, its long-term evolution remains controversial, largely due to ambiguities in existing proxy interpretations and discrepancies between records. Here, we present a weathering and erosion reconstruction from the WPWP spanning the last 140,000 years, based on the mineralogy and geochemistry of a sediment core from offshore of northern New Guinea. The paleo-weathering reconstruction is consistent with the simulated precipitation evolution on nearby islands, thereby suggesting a close coupling between climate variability and island weathering in a tropical setting. In addition, our combined data-model interpretation of WPWP climate history shows many similarities to the East Asian Summer Monsoon (EASM) variability over orbital timescales. Overall, our study highlights the critical role of precession-paced interhemispheric energy redistribution, via the West Pacific meridional sea-surface pressure gradient, in linking orbital-scale WPWP climate and EASM variability.

Emergent constraint on the projected central equatorial Pacific warming and northwestern Pacific monsoon trough change

The northwestern Pacific monsoon trough (NWPMT) deeply impacts socio-economic development and human security over East Asia by supplying moisture to the summer monsoon rainfall and modulating tropical cyclone activities. However, considerable inter-model spreads in the coupled model inter-comparison project phase 6 models make the future projection of the NWPMT less reliable. Here, we find that the inter-model spread of the NWPMT change is significantly correlated with the central equatorial Pacific sea surface temperature change, and mainly determined by the equatorial thermocline sharpness in the historical simulations. According to the emergent constraint method, the central equatorial Pacific SST would warm up about 6% slower than the multi-model mean with 56% uncertainty reduced. Correspondingly, the NWPMT would slacken westward with 36% uncertainty reduced. Results here emphasize the importance of examining and reducing systematic model biases in simulating thermocline sharpness that have been overlooked in past literatures, before achieving more reliable future projections.