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Although influences of the Atlantic multidecadal variability (AMV) and atmospheric heat source over the Tibetan Plateau (TPHS) on the East Asian summer rainfall (EASR) have been previously investigated, the relationship between the AMV and TPHS and their synergistic impact on the EASR are still unclear. We investigate the distinct relationship between the AMV and TPHS, and the role of the Tibetan Plateau (TP) on the impact of AMV on the EASR in this study. Results show that the AMV exerts a remote effect on the EASR through an atmospheric teleconnection, and the TP serves as a booster of this remote effect. The warming of the North Atlantic (positive phase of AMV) enhances the Asian summer monsoon through a zonal wave train along the northern midlatitudes, yielding an anomalous tripole rainfall pattern over East Asia. The enhanced warm and moist monsoon airflow converges and climbs up along the southern and eastern flanks of the TP, resulting in stronger latent heating over the TP than over other regions along the same latitude, due to the orographic effect of the huge plateau. The enhanced TPHS, in turn, further strengthens the summer monsoon and the East Asian tripole rainfall pattern by exciting a downstream meridional wave train. When the AMV and TPHS are in phase, the zonal wave train originating from the North Atlantic is strong and propagates eastward to the Asia–Pacific regions, significantly regulating the East Asian summer monsoon. Notably, the TP boosts this remote impact of the AMV through the effect of superimposition. Significance Statement The Atlantic multidecadal variability and atmospheric heat source over the Tibetan Plateau have been proposed as key drivers of the decadal–multidecadal climate variability in East Asia. In this study, we reveal a distinctive relationship between the Atlantic multidecadal variability and atmospheric heat source over the Tibetan Plateau. Moreover, our study shows that the Atlantic multidecadal variability exerts a remote effect on the East Asian summer rain through a zonal atmospheric teleconnection, and the Tibetan Plateau serves as a booster of this remote effect. Our results would be important for the understanding and predicting the decadal–multidecadal variations of summer climate in East Asia.

Using the multimodel simulations from phase 6 of the Coupled Model Intercomparison Project (CMIP6), we investigate the aridity changes in China and the associated mechanisms during the three geological periods of the Last Interglacial (LIG), Last Glacial Maximum (LGM), and mid-Holocene (MH), as well as the three future scenarios of the shared socioeconomic pathways of SSP1-2.6, SSP2-4.5, and SSP5-8.5. The aridity index is used to measure terrestrial moisture, which combines the effects of both precipitation and potential evapotranspiration (PET), with the latter representing the amount of water consumed by the atmosphere. The results show that relative to the preindustrial period, the total dryland area in China varies by −15%, 6%, and −13% during the LIG, LGM, and MH, respectively, and slightly varies in the three future scenarios. Over China, LGM dryland expansion and future dryland contraction are mainly attributed to precipitation changes, MH dryland contraction is mainly caused by PET changes, and LIG dryland contraction is comparably caused by PET and precipitation changes. For the LGM and three future scenarios, temperature is the leading factor of PET changes, while during the MH and LIG, the change in relative humidity is the main factor. In comparison, the simulated aridity changes in China are generally consistent with the reconstructed moisture changes for the three past periods, although uncertainties exist in reconstructions during the LGM and MH.

The East Asian summer monsoon (EASM) and associated summer precipitation patterns over eastern China have exhibited interannual and interdecadal variations in recent decades, but whether the precipitation modes vary with climate conditions remains unclear. In this study, we investigate the changes in summer precipitation modes over eastern China and associated mechanisms in simulated past and future warm periods, namely, the last interglacial (LIG), mid-Holocene, and the twenty-first century under the Shared Socioeconomic Pathway (SSP) based on representative concentration pathway 8.5 (SSP5–8.5) scenario, using Coupled Model Intercomparison Project Phase 6 (CMIP6) models. The model evaluation indicates that only one out of nine CMIP6 models, specifically the Community Earth System Model, version 2 (CESM2), can well reproduce the observed summer precipitation modes at the present. The empirical orthogonal function (EOF) analyses of the CESM2 simulations reveal that during the warm periods induced by either orbital parameters or greenhouse gas concentrations, the first leading mode of summer precipitation switches from its present meridional tripolar structure to a dipole pattern, and the second leading mode is generally a meridional tripolar mode that differs from the present dipole pattern. This summer precipitation regime interchange in the warm intervals is associated with the formation of the dipole and tripolar circulation patterns. The large-scale circulation changes responsible for the altered precipitation modes are attributed to the enhanced EASM and relevant southerly winds due to intensified land–sea thermal contrast, although the external forcings and the magnitude of EASM enhancement are different in the interglacial and future periods.

Using all relevant climate experiments archived in phases 3 and 4 of the Paleoclimate Modeling Intercomparison Project (PMIP3/4), we examine the interannual variability change in global-scale surface air temperature and associated physical mechanisms during the Last Glacial Maximum (LGM). The results show that relative to the preindustrial period, the LGM interannual temperature variability increased by 20% globally, which was mainly attributed to the large-scale increase in the meridional temperature gradient, especially at midlatitudes. Larger magnitudes of change occurred in areas where the underlying surface properties, such as the surface altitude, land–sea distribution, and ice sheet extent, differed from those in the preindustrial period. In addition, the relationship between changes in the meridional temperature gradient and the interannual temperature variability became closer in the winter hemisphere. In the tropical land regions, changes in interannual temperature variability are mainly related to the adjustment of latent and sensible heat fluxes during the LGM.

The late Pliocene warm period, approximately 3.0 to 3.3 million years ago, is the most recent geological warm period in the Earth’s history. We used PlioMIP simulations together with proxy evidence to investigate the westerlies and paleomonsoon variation in the late Pliocene warm period.Compared to the pre-industrial period, the simulated westerlies generally shifted poleward with a dipole pattern, and were closely related to the change of the tropospheric meridional temperature gradient as a result of thermal structure adjustment. Convincing geological evidences from the North Pacific deep-sea sites supported the major features of the simulated North Pacific westerlies. The simulated global land monsoon system enhanced in terms of area and monsoon precipitation, mainly over northern Africa, Asia, and northern Australia, and was roughly consistent with the reconstructions. The anomalous inland water vapor transportation together with the variation of vertical moisture advection and evaporation, explains most of the global land monsoon changes.The poleward shift of the westerlies and global land monsoon systems corresponded to the poleward shift of the mean meridional circulation. The sea surface temperatures and sea ice contributed to the model spread of the westerly anomalies and global land monsoon. The poleward shift and intensified Asian monsoon, and/or an overall intensified global land monsoon in the late Pliocene warm period is hypothesized to contribute to the lowering of atmospheric CO2 concentration and the subsequent onset of the sustained major Northern Hemisphere glaciation, through the impact on and feedback from the terrestrial carbon cycle process., The 28th IUGG General Assembly (IUGG2023) (Berlin 2023)

The Atlantic Meridional Overturning Circulation (AMOC) is a key feature of the North Atlantic with global ocean impacts. The AMOC's response to past changes in forcings during the Holocene provides important context for the coming centuries. Here, we investigate AMOC trends using an emerging set of transient simulations using multiple global climate models for the past 6,000 years. Although some models show changes, no consistent trend in overall AMOC strength during the mid-to-late Holocene emerges from the ensemble. We interpret this result to suggest no overall change in AMOC, which fits with our assessment of available proxy reconstructions. The decadal variability of the AMOC does not change in ensemble during the mid- and late-Holocene. There are interesting AMOC changes seen in the early Holocene, but their nature depends a lot on which inputs are used to drive the experiment.

The Upper Indus Basin (UIB) supplies water resources for the downstream areas of the Indus Basin, and the associated climate changes have attracted considerable attention. Here, we project the aridity changes in the UIB during the 21st century relative to 1995-2014 based on 12 Coupled Model Intercomparison Project Phase 6 (CMIP6) models under the 3 Shared Socioeconomic Pathway (SSP) scenarios. The aridity index (AI), defined as the ratio of annual precipitation to potential evapotranspiration (PET), is applied to quantify the dry conditions. According to the median of the preferred models, the annual mean temperature is projected to increase continually in the UIB across the 21st century under SSP2-45 and SSP5-85, and it increases before the 2050s and then stabilizes afterwards under SSP1-26. Generally, PET will increase and AI will decrease (a drying trend) in the UIB during the 21st century. The regionally averaged AI over the UIB linearly decreases as global warming intensifies at a slope of 0.1 °C-1 under both SSP2-45 and SSP5-85. Remarkable increases in aridity occur in the northern and northwest parts of the UIB. Seasonally, the largest decrease in AI is seen in December-January-February, and the smallest occurs in June-�July-August. Furthermore, PET plays a key role in AI changes, excluding the southeast part of UIB, and the percent contribution of PET to AI changes tends to increase over time in the 21st century. Overall, AI and PET changes are primarily determined by thermodynamic factors in the UIB.

An unprecedented cold wave intruded into East Asia in early January 2021 and led to record-breaking or historical extreme low temperatures over vast regions. This study shows that a major stratospheric sudden warming (SSW) event at the beginning of January 2021 exerted an important influence on this cold wave. The major SSW event occurred on 2 January 2021 and subsequently led to the displacement of the stratospheric polar vortex to the East Asian side. Moreover, the SSW event induced the stratospheric warming signal to propagate downward to the mid-to-lower troposphere, which not only enhanced the blocking in the Urals–Siberia region and the negative phase of the Arctic Oscillation, but also shifted the tropospheric polar vortex off the pole. The displaced tropospheric polar vortex, Ural blocking, and another downstream blocking ridge over western North America formed a distinct inverted omega-shaped circulation pattern (IOCP) in the East Asia–North Pacific sector. This IOCP was the most direct and impactful atmospheric pattern causing the cold wave in East Asia. The IOCP triggered a meridional cell with an upward branch in East Asia and a downward branch in Siberia. The meridional cell intensified the Siberian high and low-level northerly winds, which also favored the invasion of the cold wave into East Asia. Hence, the SSW event and tropospheric circulations such as the IOCP, negative phase of Arctic Oscillation, Ural blocking, enhanced Siberian high, and eastward propagation of Rossby wave eventually induced the outbreak of an unprecedented cold wave in East Asia in early January 2021.

Warming-induced topographic changes of the East Antarctic ice sheet (EAIS) during the Pliocene warm period could have a significant influence on the climate. However, how large changes in the EAIS height could theoretically affect global climate have yet to be studied. Here, the influence of possible height changes of the EAIS on climate over the East Antarctic ice sheet region versus the rest of the globe is investigated through numerical climate modeling using the Pliocene as a test case. As expected, the investigation reveals that the reduction of ice sheet height leads to a warmer and wetter East Antarctica. However, unintuitively, both the surface air temperature and the sea surface temperature decrease over the rest of the globe. These temperature changes result from the higher air pressure over Antarctica and the corresponding lower air pressure over extra-Antarctic regions with the reduction of EAIS height. This topography effect is further confirmed by energy balance analyses. These findings could provide insights into future climate change caused by warming-induced height reduction of the Antarctic ice sheet.

This study presents a comprehensive analysis of the synergistic impacts of the Atlantic multidecadal oscillation (AMO) and Pacific decadal oscillation (PDO) on the interdecadal variations of summer rainfall in Northeast Asia. Following the construction of four probable scenarios under various combinations of the AMO and PDO phases, it is found that when the AMO and PDO are out of phase, both of them induce a strong or weak East Asian summer monsoon and a low or high pressure system over Northeast Asia through atmospheric teleconnection, which results in significant wet or dry conditions over the whole of Northeast Asia through the effects of superimposition. In contrast, when the AMO and PDO are in-phase, they induce moderate and regional wet or dry conditions in Northeast Asia, and only a slightly strong or weak East Asian summer monsoon through the effects of cancellation. During the mid-1960s–1990s, a period of drought first began in Northeast Asia under a negative AMO and negative PDO in the mid-1960s, which then increased in severity under a negative AMO and positive PDO in the 1980s, before finally coming to an end under a positive AMO and negative PDO in the late 1990s. The interdecadal predictability of summer rainfall in Northeast Asia may reside in the interdecadal behavior of the North Atlantic and Pacific Oceans.

This study investigates the characteristics and physical mechanisms of the multidecadal variations in the East Asian winter (December–February) monsoon (EAWM) since 1850 based on multiple observational and reanalysis datasets. The results indicate that the EAWM undergoes multidecadal weakening during the periods of 1869–1919 and 1986–2004 but strengthening during the period of 1920–85. Similar evolutions can be observed in the time series of the area-averaged winter surface air temperature over East Asia. Associated with the EAWM multidecadal variations, a quasi-barotropic Rossby wave train originating from the subtropical North Atlantic propagating across the Eurasian continent to Northeast Asia also experiences phase shifting at the same time. In its positive phase, the low-level anticyclonic anomaly over the northern Eurasian continent causes a stronger Siberian high; the mid- and high-level cyclonic anomalies over Northeast Asia deepen the East Asian trough and strengthen the East Asian jet stream, respectively. Thus, the positive phase of the wave train is conducive to stronger EAWMs and vice versa. The diagnostic analysis of the Rossby wave source indicates that the upper-tropospheric divergence anomalies over the North Atlantic can favor the excitation of this wave train, and the feedback forcing of high-frequency eddies plays important roles in its maintenance. In addition, the phase shifting of the Atlantic multidecadal oscillation (AMO) can induce a similar Rossby wave train across the Eurasian continent, through which it further modulates the multidecadal variations in the EAWM. Warm phases of the AMO are favorable for a stronger EAWM and colder midlatitude Eurasian continent and vice versa.

Global warming is a widely concerned topic, and the surface temperature has shown an accelerated warming trend during the past several decades. From the perspective of a longer time scale, the 20th century (1900–2000) could be the warmest period in the last millennium, and the global or hemispheric averaged temperature over this period is higher than that over other centuries, particularly compared with that over the Little Ice Age (LIA; 1450–1850). However, we recently found that, in the reconstruction, the 20th-century temperature over some northern mid-latitude regions could be significantly lower than that during the LIA, which contradicts our previous perceptions regarding global warming. Modeling results from the Last Millennium Ensemble Project also reproduce a similar phenomenon, that is, the 20th-century cooling over some northern mid-latitude regions (CNMR). The simulated CNMR can be found in all four seasons. Further analysis indicates that the cooling effects from ozone-aerosol and land use forcings, overcoming greenhouse gas and solar forcing induced warming, play dominant roles in causing the CNMR. The ozone-aerosol forcing reduces the surface net shortwave flux through both direct aerosol–radiation interaction and atmosphere–cloud feedback, while the land use forcing causes negative net shortwave flux anomalies through modulation of surface albedo. Overall, the ozone-aerosol and land use forcings shape the CNMR phenomenon by inducing anomalous surface net shortwave flux, with the ozone-aerosol forcing playing a dominant role. This study highlights the important influences of ozone-aerosol and land use cooling effects on local climate.

Warming-induced topographic changes of the East Antarctic Ice Sheet (EAIS) could have significant influence on the climate. However, how large changes in the EAIS height could theoretically affect global climate have yet to be studied. Here, the influence of possible height changes of the EAIS on climate is investigated through numerical climate modeling, using the Pliocene as a test case. As expected, the investigation reveals that the reduction of ice sheet height leads to a warmer and wetter East Antarctica. However, unintuitively, both the surface air temperature and the sea surface temperature decrease over the rest of the globe. These temperature changes result from the higher air pressure over Antarctica and the corresponding lower air pressure over extra-Antarctic regions with the reduction of EAIS height. This topography effect is further confirmed by energy balance analyses. These findings could provide insights into future climate change caused by warming-induced height reduction of the Antarctic ice sheet.

Stratospheric aerosol intervention (SAI) geoengineering is a proposed scheme to counteract anthropogenic global warming, but the climate response to SAI, with great regional disparities, remains uncertain. In this study, we use Geoengineering Model Intercomparison Project G4 experiment simulations from six models that counteract anthropogenic forcing under medium–low emissions (Representative Concentration Pathway 4.5 – RCP4.5) by injecting a certain amount of SO2 into the stratosphere every year to investigate the surface air temperature response to SAI geoengineering over China. We have found that SAI has led to surface cooling over China during the last 40 years of injection simulation (2030–2069), which varies among models, regions, and seasons. Decreased tropospheric temperature and water vapor and increased stratospheric aerosols induce robust decreases in downward clear-sky longwave and shortwave radiation fluxes at the surface, respectively, dominating the temperature change over China. Changes in cloud effective forcing and surface albedo feedback also relate to the temperature response but with large spatial and seasonal variations. We find that the increased summer cloud cover and winter surface albedo lead to strong cooling, while the decreased summer cloud cover and winter surface albedo lead to weak cooling or even insignificant warming for the certain subregions and models. Our results suggest that cloud and land surface processes in models dominate the spatial pattern of SAI-induced surface air temperature change over China.

The evolution of central Asian drylands during the Cenozoic is a hot topic in paleoclimate research, but the underlying mechanism remains unclear. Here, we investigate this topic with climate modeling based on six key geological periods. Our results indicate that central Asian drylands have existed since the early Eocene, after which they move northward and become narrower. Although changed land–sea distribution and decreased atmospheric CO2 concentration promote the aridification of drylands, they only slightly affect the latitudinal distribution of drylands. By comparison, the growth of Asian high-topography areas, especially the Tibetan Plateau (TP), makes central Asian drylands move northward, concentrate in narrow latitudinal bands, and increase in intensity. Good model-data qualitative agreement is obtained for stepwise aridification in midlatitude inland Asia north of ~40°N, and the uplifted main and northern TP by the early Miocene likely forced drylands to change in this region.

Improvement in the seasonal forecasting of East Asian summer monsoon rainfall (EASMR) remains a great challenge, as it is influenced by varied and complex impacts from (1) external forcings and slowly varying internal variabilities, which are potentially predictable, and (2) internal dynamics on intraseasonal time scales, which is basically unpredictable beyond a season. In this work, a (co-)variance decomposition method is applied to identify the leading potentially predictable (slow) patterns of the EASMR [the seasonal mean rainfall in the region (100°E–140°E, 5°N–50°N) in June–July–August] during 1979–2019 by separating the unpredictable noise (intraseasonal). We focus on the most critical predictable sources that are additional to the decaying (DC) El Niño–Southern Oscillation (ENSO), developing (DV) ENSO, and spring Arctic Oscillation (AO) – the three most important and well-recognized predictors for EASMR. We find that (1) the indices that represent the EASMR predictability related to the DC ENSO, spring AO and DV ENSO are the preceding November to March Niño 1+2 sea surface temperature (SST), the April–May AO, and the May Niño 4 SST, respectively; (2) the dominant additional predictable EASMR signals that are linearly independent of the DC ENSO, spring AO and DV ENSO have apparent relationships with the interannual variability of the SST in the western North Pacific, tropical and southern Atlantic, southern Indian, and Arctic oceans during boreal springtime, as well as the linear trend; and (3) by applying a principal component regression scheme to evaluate the EASMR predictability arising from DC/DV ENSO–AO and these additional predictors, the cross-validated fraction variance skill of the total seasonal mean EASMR is 11% (8%–land; 13%–ocean) for the former, and 15% (15%–land; 15%–ocean) for the latter, with a total of 26% that comprises more than 80% of the potential predictability of the EASMR. The considerable skill stemming from the predictors additional to DC/DV ENSO–AO indicates that they are worthy of attention in the seasonal forecasting of EASMR, especially for terrestrial areas.

The concept of climate sensitivity emerges for a quantitative measurement of the amount of warming in association with the increase of atmospheric CO2 concentration. Here we provide a perspective on the climate sensitivity and associated transient climate response using the latest literature, both of which have been highly concerned in recent decades.

To date, climate records have mainly shown three different trends of Holocene precipitation evolution in northeastern (NE) China, and the underlying mechanisms remain unclear. Here, we use model results from Holocene transient climate simulations conducted by the Community Climate System Model version 3 to investigate the evolution of precipitation in NE China and the associated mechanisms. The model results indicate that precipitation changes within NE China show obvious spatial discrepancies. In particular, the annual precipitation maximum occurs in the early Holocene for the western subregion, while it occurs in the mid-late Holocene for the eastern subregion. These results show two different trends of Holocene precipitation within NE China capturing the large-scale precipitation changes appearing in climate records. These spatial features are closely related to the gradual weakening of the East Asian summer monsoon during the Holocene and are mainly attributed to the combined effects of orbital forcing and the ice sheet. Changes in orbital parameters play a major role in the decreased precipitation in the western subregion, while changes in the ice sheet contribute more to the increased precipitation in the eastern subregion. The observed model-data discrepancy partly relates to the low horizontal resolution employed and the physical processes and parameterizations of the model used.

The teleconnection between the Atlantic Multidecadal Oscillation (AMO) and eastern China summer precipitation (ECSP) for the modern period has been emphasized in the past few decades. We test its stability during the Medieval Climate Anomaly (MCA) and Little Ice Age (LIA) based on the composite results of the median of six models under the Paleoclimate Modeling Intercomparison Project Phase3 (PMIP3) framework. During the MCA, ECSP generally increases in positive AMO phases relative to negative phases, similar to the modern teleconnection, while during the LIA, the precipitation tends to reduce over eastern China, especially in the Yangtze River basin. Decomposing the precipitation change on the basis of a diagnostic moisture budget manifests that the different AMO-related precipitation changes stem from distinct effects of circulation-induced moisture convergence during the two periods. Compared with negative AMO phases, positive AMO phases during the MCA show an anomalous lower-level cyclone and upper-level anticyclone over eastern China that facilitate the upward motion anomaly and precipitation excess. During the LIA, a barotropic anticyclone centers in Northeast China and weakens the high-level westerlies over eastern China; this favors descending and upper-level divergence anomalies and leads to precipitation decreases. The distinct convergence changes are determined by differing propagation paths of the AMO-induced teleconnection wave train during the two periods.

We compare the ability of coupled global climate models from the phases 5 and 6 of the Coupled Model Intercomparison Project (CMIP5 and CMIP6, respectively) in simulating the temperature and precipitation climatology and interannual variability over China for the period 1961\2-2005 and the climatological East Asian monsoon for the period 1979–2005. All 92 models are able to simulate the geographical distribution of the above variables reasonably well. Compared with earlier CMIP5 models, current CMIP6 models have nationally weaker cold biases, a similar nationwide overestimation of precipitation and a weaker underestimation of the southeast\3-northwest precipitation gradient, a comparable overestimation of the spatial variability of the interannual variability, and a similar underestimation of the strength of winter monsoon over northern Asia. Pairwise comparison indicates that models have improved from CMIP5 to CMIP6 for climatological temperature and precipitation and winter monsoon but display little improvement for the interannual temperature and precipitation variability and summer monsoon. The ability of models relates to their horizontal resolutions in certain aspects. Both the multi-model arithmetic mean and median display similar skills and outperform most of the individual models in all considered aspects.

Changes in extreme climate have caused widespread concern, and it is important to understand how climate extremes will link to global warming intensity at the regional scale. Based on the daily minimum and maximum temperature and precipitation outputs from 25 Coupled Model Intercomparison Project Phase 5 (CMIP5) climate models under the Representative Concentration Pathways 8.5 (RCP8.5) scenario, we project the linkage of future regional climate extremes to the global mean temperature increase above preindustrial levels. Results show that regionally averaged changes in absolute temperature extremes (the coldest night and the warmest day) scale linearly with global warming intensity. In contrast, changes in cold nights and cold days in all regions, warm nights in low latitudes, and warm days in Southeast Asia exhibit nonlinear relationships with the global mean temperature increase, which manifests rapid changes in early warming stages and weak changes in late warming stages. The percentile-based temperature extremes vary at large magnitudes as global warming intensifies in low latitudes, while large values are seen in middle and high latitudes for the coldest night and warmest day, respectively; large intermodel spread occurs in the strong scaling areas, except for cold days and cold nights. Regional mean changes in extreme precipitation show consistent linear trends with global warming, and different indices vary in magnitude with region. Extreme heavy precipitation events increase linearly with global warming in high latitudes with larger magnitudes. The intermodel spread is generally large in low latitudes and will increase with warming. The work presented here can provide effective support to decision makers for developing adaptation and mitigation measures.

The assumption of a stationary global signal linked to El Niño–Southern Oscillation (ENSO) events is often used in paleo-ENSO proxy data interpretation. This paper attempts to investigate whether the assumption is valid during the last glacial maximum (LGM) over the region 60°S–90°N, 60°E−60°W. Using four models within phase 3 of the Paleoclimate Modeling Intercomparison Project framework that well reproduce ENSO-induced variabilities, differences from the preindustrial period to LGM in the ENSO-related sea surface temperature pattern and its impacts are investigated. Compared to the preindustrial period, the ENSO impacts are revealed to weaken and shift eastward during the LGM. According to multimodel medians, ENSO impacts on precipitation and near-surface air temperature are attenuated over most regions of concern, with percentage changes in both parameters averaging −21% for the whole region; the ENSO-induced Pacific–North America (PNA) teleconnection pattern is weakened, manifested by the 41% diminished center over the North Pacific and the almost vanished activity centers over the continent. Spatially, there is a zonal contraction of 13° for the sea surface warming of ENSO, as well as eastward migration over 10° for the ENSO-induced positive precipitation anomaly center over the tropical Pacific and the PNA teleconnection pattern outside the tropics. The aforementioned changes are linked to the altered climatic background during the LGM, which features a 16° eastward shift for the Pacific Walker circulation rising branch and a weakened waveguide in the midlatitudes. The results suggest that the hypothesis of stationary ENSO impacts should be applied cautiously to the past.

The East Asian summer monsoon (EASM) intensified during the early to mid-Holocene relative to the present primarily due to orbital forcing. However, on the regional scale, changes in the monsoonal precipitation exhibit considerable spatial disparity, and the underlying mechanisms remain unresolved. In this study, the dynamic processes responsible for the difference of the EASM precipitation between the mid-Holocene and preindustrial period are systematically examined using the CMIP5 multimodel simulations. The moisture budget diagnostic identifies vertical motion as the key factor determining the cross-like precipitation pattern in East Asia. Relative to the preindustrial period, the mid-Holocene anomalous ascending motion corresponds well with the excessive precipitation over northern and southern China, and vice versa for west-central China, the Korean peninsula, Japan, and its marginal seas. In the framework of the moist static energy budget, the increased insolation and the attendant intensification of land–sea thermal contrast give rise to anomalous ascending motions, while descending motions are fundamentally forced by the decreased latitudinal insolation gradient. In particular, thermodynamic changes, namely, the reduced pole–equator temperature and humidity gradients, account for the downward motions over the northwestern Pacific. Dynamic changes, namely, the weakened westerlies, play a leading role in suppressing updrafts in west-central China. This study highlights that the orbital-scale monsoonal precipitation changes are not solely determined by local radiative forcing as repeatedly emphasized before. The latitudinal uneven distribution of insolation is crucial to explain the spatial inhomogeneity in the EASM precipitation changes during the Holocene.

Based on surface air temperature and precipitation observation data and NCEP/NCAR atmospheric reanalysis data, this study evaluates the prediction of East Asian summer climate during 1959–2016 undertaken by the CESM (Community Earth System Model) large-ensemble initialized decadal prediction (CESM-DPLE) project. The results demonstrate that CESM-DPLE can reasonably capture the basic features of the East Asian summer climate and associated main atmospheric circulation patterns. In general, the prediction skill is quite high for surface air temperature, but less so for precipitation, on the interannual timescale. CESM-DPLE reproduces the anomalies of mid- and high-latitude atmospheric circulation and the East Asian monsoon and climate reasonably well, all of which are attributed to the teleconnection wave train driven by the Atlantic Multidecadal Oscillation (AMO). A transition into the warm phase of the AMO after the late 1990s decreased the geopotential height and enhanced the strength of the monsoon in East Asia via the teleconnection wave train during summer, leading to excessive precipitation and warming over East Asia. Altogether, CESM-DPLE is capable of predicting the summer temperature in East Asia on the interannual timescale, as well as the interdecadal variations of East Asian summer climate associated with the transition of AMO phases in the late 1990s, albeit with certain inadequacies remaining. The CESM-DPLE project provides an important resource for investigating and predicting the East Asian climate on the interannual and decadal timescales.

The eastern China summer precipitation is related to the Pacific Decadal Oscillation (PDO) on interdecadal time scales in modern times, but it remains unclear whether such a relationship holds prior to the instrumental period. We examine this relationship during the Medieval Climate Anomaly (MCA) and Little Ice Age (LIA). According to a composite analysis using simulations of the HadCM3 model, which is selected from nine available climate models, the PDO–eastern China summer precipitation relationship varies with climatic background. The modern relationship features deficient precipitation over North and South China and excessive precipitation in the Yangtze–Huai River Valley in positive PDO phases compared with negative phases. In contrast, there is more precipitation over South and North China but less in the Yangtze–Huai River Valley during the MCA and widespread below-normal summer precipitation over eastern China during the LIA. Such different PDO-related precipitation patterns between the MCA and LIA are closely linked to distinct changes in local atmospheric circulation. Compared with negative PDO phases, positive phases during the MCA show an anomalous Pacific–Japan/East Asia–Pacific pattern over East Asia and strengthened high-level westerlies centering on 120°E and 25–30°N, which lead to the triple pattern in the precipitation anomaly. During the LIA, a cyclonic anomaly occurs over the South China Sea–Philippine Sea in the lower and middle troposphere, and two upper-level low trough anomalies occur over East Asia, causing the anomalous precipitation deficit. The different PDO-related local circulations are found to be relevant to the thermodynamic effect of low-latitude sea surface temperature and summer precipitation over India, as well as the propagation of upstream wave trains.

The Holocene, which started approximately 11.5 ka, is the latest interglacial period with several rapid climate changes with timescales, from decades to centuries, superimposed on the millennium-scale mean climate trend. Climate models provide useful tools to investigate the underlying dynamic mechanisms for the climate change during this well-studied time period. Thanks to the improvements in the climate model and computational power, transient simulation of the Holocene offers an opportunity to investigate the climate evolution in response to time-varying external forcings and feedbacks. Here, we present the design of a new set of transient experiments for the whole Holocene from 11.5 ka to the preindustrial period (1850; HT-11.5 ka) to investigate both the combined and separated effects of the main external forcing of orbital insolation, atmospheric greenhouse gas (GHG) concentrations, and ice sheets on the climate evolution over the Holocene. The HT-11.5 ka simulations are performed with a relatively high-resolution version of the comprehensive Earth system model CESM1.2.1 without acceleration, both fully and singly forced by time-varying boundary conditions of orbital configurations, atmospheric GHGs, and ice sheets. Preliminary simulation results show a slight decrease in the global annual mean surface air temperature from 11.5 to 7.5 ka due to both changes in orbital insolation and GHG concentrations, with an abrupt cooling at approximately 7.5 ka, which is followed by a continuous warming until the preindustrial period, mainly due to increased GHG concentrations. Both at global and zonal mean scales, the simulated annual and seasonal temperature changes at 6 ka lie within the range of the 14 PMIP4 model results and are overall stronger than their arithmetic mean results for the Middle Holocene simulations. Further analyses on the HT-11.5 ka transient simulation results will be covered by follow-up studies.

International audience; The evolution of central Asian drylands during the Cenozoic is a hot topic in paleoclimate research, but the underlying mechanism remains unclear. Here, we investigate this topic with climate modeling based on six key geological periods. Our results indicate that central Asian drylands have existed since the early Eocene, after which they move northward and become narrower. Although changed land-sea distribution and decreased atmospheric CO2 concentration promote the aridification of drylands, they only slightly affect the latitudinal distribution of drylands. By comparison, the growth of Asian high-topography areas, especially the Tibetan Plateau (TP), makes central Asian drylands move northward, concentrate in narrow latitudinal bands, and increase in intensity. Good model-data qualitative agreement is obtained for stepwise aridification in midlatitude inland Asia north of ~40°N, and the uplifted main and northern TP by the early Miocene likely forced drylands to change in this region.

During January 21–24, 2016, most land areas in the Northern Hemisphere experienced extreme low temperatures. In North America, a historic snowstorm hit the northern and eastern United States. In East Asia, an unprecedented cold wave occurred and led to record‐breaking low temperatures in many regions. In this study, observational analyses revealed that both extreme events were triggered by a remarkable change in atmospheric circulation in the Arctic region in early January 2016, which switched from a concentric ring pattern to a dipole pattern. The dipole pattern resulted in two inverted Ω‐shaped circulation patterns that dominated the North America and East Asia. The inverted Ω‐shaped circulation patterns induced remarkable tropopause folding, which conveyed high‐potential‐vorticity cold air downwards from the lower stratosphere of Arctic to the middle and lower troposphere of North America, which increased cyclonic vorticity and negative height perturbations, and converged with moist air from the western North Atlantic and Gulf Stream, resulting in a severe snowstorm in the northern and eastern United States from 22 to 24 January. In East Asia, the tropopause folding transported high‐potential‐vorticity cold air downwards to the middle and lower troposphere of East Asia, resulting in the outbreak of a severe cold wave in East Asia from 21 to 24 January.