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The Asian monsoon influences the lives of more than a third of the world's population, and understanding its spatial and temporal variability is fundamental to sustainable development. The complex dynamics of this climatic system are therefore of broad scientific and societal interest. In this virtual special issue (VSI), we present 19 papers dealing with the Asian monsoon since the Last Glacial Maximum (LGM, ∼21 kyr BP), with a focus on understanding variability and forcing mechanisms. Findings use recently developed quantitative reconstructions combined with numerical simulations, and present novel insights as follows: (1) analyses of comprehensive datasets of pollen, diatom, brGDGTs, oxygen and hydrogen isotopes and frequency magnetic susceptibility, as well as an innovative algorithm model for the lake energy-water balance, improve the reliability of quantitative reconstructions of Asian monsoon climate variations; (2) studies of quantitative climate parameters in central East Asia show that mean annual temperature (MAT) was ∼5 °C (or ∼ 7.9 °C using brGDGTs) lower during the LGM, ∼1.5 °C (±41% using brGDGTs) higher around the Holocene thermal optimum (HO) and mean annual precipitation (MAP) varied between 30 and 150% with marked seasonality during 8–5 ka; (3) dynamical downscaling palaeoclimatic simulations improve the accuracy of past monsoon variations, revealing strong variability in monsoon precipitation across the LGM and HO. The holistic study of Asian monsoon variations at orbital to centennial timescales in these VSI papers presents reliable observations of monsoon variability and its driving mechanisms, providing high-resolution quantitative paleoclimate reconstructions that fill existing gaps in spatial coverage, as well as offering an improved understanding, thorough numerical simulation, of coupled sea-level change and vegetation feedbacks. • An introduction to Asian monsoon variations over the past 21 ka. • Transfer functions, sedimentary records and numerical simulation are developed for studying past Asian monsoon. • Averaged MAP in East Asia varied between 30-150 % over the past 21 ka. [ABSTRACT FROM AUTHOR]

The Asian monsoon has progressively become a megamonsoon system since the early Cenozoic. To improve our understanding of the complex nature of the Asian monsoon system, involving strong interactions between atmospheric, oceanic and terrestrial systems across different timescales, we present this special issue, entitled Cenozoic climate change in Asia. The special issue is dedicated to Prof. Zhengtang Guo in honour of his distinguished contributions as Editor-in-Chief of Global and Planetary Change to our understanding of the long-term evolution of the Asian monsoon system. The special issue consists of nineteen papers, grouped into three categories, that address Cenozoic climate change, mainly in Asia. The first category focuses on the plate tectonic-scale and considers how changes in palaeogeography and palaeotopography have shaped climate evolution. The second category addresses orbital- to suborbital-scale climate change and, in particular, explores the links between low-latitude insolation, high-latitude ice sheets and the Asian climate. The third category addresses millennial- to decadal-scale climate changes. In addition, past human-environment interactions are also discussed. These studies provide important insights into our understanding and prediction of both natural variability and human-induced climate changes in Asia and their linkages with global climate within the Earth System. • This special issue dedicated to Prof. Zhengtang Guo. • Asian climate variabilities across multiple time scales. • Past human-environment interactions in monsoonal East Asia. • Integration of Earth's interior and surface tectonic-climatic processes. [ABSTRACT FROM AUTHOR]

The relationship between initial Homo sapiens dispersal from Africa to East Asia and the orbitally paced evolution of the Asian summer monsoon (ASM)--currently the largest monsoon system--remains underexplored due to lack of coordinated synthesis of both Asian paleoanthropological and paleoclimatic data. Here, we investigate orbital-scale ASM dynamics during the last 280 thousand years (kyr) and their likely influences on early H. sapiens dispersal to East Asia, through a unique integration of i) new centennial-resolution ASM records from the Chinese Loess Plateau, ii) model-based East Asian hydroclimatic reconstructions, iii) paleoanthropological data compilations, and iv) global H. sapiens habitat suitability simulations. Our combined proxy-and model-based reconstructions suggest that ASM precipitation responded to a combination of Northern Hemisphere ice volume, greenhouse gas, and regional summer insolation forcing, with cooccurring primary orbital cycles of ~100-kyr, 41-kyr, and ~20-kyr. Between ~125 and 70 kyr ago, summer monsoon rains and temperatures increased in vast areas across Asia. This episode coincides with the earliest H. sapiens fossil occurrence at multiple localities in East Asia. Following the transcontinental increase in simulated habitat suitability, we suggest that ASM strengthening together with Southeast African climate deterioration may have promoted the initial H. sapiens dispersal from their African homeland to remote East Asia during the last interglacial. [ABSTRACT FROM AUTHOR]

Diatom records in tropical settings have been used to appraise paleomonsoons throughout the Quaternary period due to their ubiquitous presence, rapid response, and preservation in sediments. Despite this, diatoms have been rarely used to assess the Asian monsoonal climate. As the Asian monsoon comprises the Indian and East Asian subsystems, it plays a significant role in global hydrological and energy cycles. Keeping global climate in mind, we reviewed the dynamics and causes of Asian monsoon variability (covering major records exclusive from the tropics) on different spatial and temporal scales using diatoms as a proxy record. The data have been compiled from 50 papers spanning fresh and marine sediment archives, covering entire monsoon regimes, predominantly from Southeast Asia. This study classified the data based on various geological periods ranging from the Pleistocene Epoch to the Holocene Meghalayan age (600 ka −300 a BP). Diatom proxies indicate fluctuating hydrological conditions and varying monsoon intensity throughout the Quaternary period and show regional scale coherence for specific climatic events. Diatom records from both inland and marine sediment archives indicate a wet and warm period during the mid–Pleistocene (590–300 kyr) and a cold climate and weakened East Asian monsoon during 300–140 kyr. Through the late Pleistocene period (75 to 15 kyr), monsoonal conditions were intense, wet and warm during the interglacial stages and weaker and dry during glacial stages across South and East Asia. During the Last Glacial Maximum (24.5–18 kyr), the monsoon significantly weakened with cold climatic conditions in southern Asia, and increased precipitation across East Asia. A majority of the published records witnessed an enhanced Asian monsoon and a warm and humid period towards the early to mid–Holocene, with a decline in the monsoon after the mid–Holocene accompanying intermittent intense wetter conditions. Diatom records from the sediment archives at many geographic locations hold signatures of extreme events such as the Younger Dryas cold event around 13.3–11.3 kyr BP, the Medieval Warm Period around 1.3 to 0.8 kyr, and the Little Ice Age in between 0.6 and 0.3 kyr. Further, we indicate that several sites from different monsoon-dominated geographic-climatic zones should be re-investigated with high resolution across spatial and temporal palaeoclimatic periods (including existing databases) with careful diatom taxonomy to strengthen a climatic reconstruction of this monsoon-dominated region of Asia. [ABSTRACT FROM AUTHOR]

The past Asian precipitation δ18O (δ18Op) records from stalagmites and other deposits have shown significant orbital-scale variations, but their climatic implications and regional differences are still not fully understood. This study, as the first attempt of a 300-kyr transient stable isotope-enabled simulation, investigated the characteristics and mechanisms of the orbital-scale δ18Op variations in three representative regions of Asia: arid Central Asia (CA), monsoonal South Asia (SA) and monsoonal East Asia (EA). The modelling results showed that the variations in the CA, SA and EA annual δ18Op exhibited significant but asynchronous 23-kyr precession cycles. Further analyses revealed that although the precession-induced insolation variation was the ultimate cause of the δ18Op variation in all three regions, the dominant mechanisms and the involved physical processes were distinct among them. For the CA region, the rainy-season (November–March) temperature effect and water vapour transport by the westerly circulation were identified as the key precession-scale processes linking the October–February boreal mid-latitude insolation to the rainy-season or annual δ18Op. In the SA region, the rainy-season (June–September) precipitation amount effect and upstream depletion of the monsoonal water vapour δ18O served as the main mechanisms linking the rainy-season or annual δ18Op to the April–July insolation variation at the precession scale. For the EA region, however, the precession-scale annual δ18Op was mainly controlled by the late-monsoon (August–September) and pre-monsoon (April–May) water vapour transport patterns, which were driven by the July–August insolation and the global ice volume, respectively. These results suggest that the climatic implications of the orbital-scale Asia δ18Op variations are sensitive to their geographic locations as determined by the combined effects of insolation and regional circulation patterns associated with the respective rainy seasons. This study provides new insights into understanding the regional differences and formation mechanisms of the Asian orbital-scale δ18Op variations. [ABSTRACT FROM AUTHOR]

Robust and uncertain sea-level pressure patterns over summertime East Asia in the future global warming projections and their causes are studied by applying the inter-model empirical orthogonal function (EOF) analysis to the multi-model experiments in the sixth phase of the Coupled Model Intercomparison Project (CMIP6) and focusing on common features with the previous CMIP5 analysis. The ensemble average and the first to third EOF modes associated with future pressure changes are similar to the corresponding modes from CMIP5. The first and second modes represent strengthened and weakened high-pressure systems in subtropical and northern East Asia, respectively. The third mode is the reverse anomaly of the climatological pressure pattern over summertime East Asia, which indicates weakened southerly monsoon winds. The second mode pattern makes positive contributions to almost all the CMIP6 future pressure changes, representing a robust future projection pattern. The robust mode is the result of surface warming over the northern continents and neighboring seas that is stronger than the global average. The first and third modes are considered to be uncertain (but major) patterns in the ensemble projections as the signs of their contributions to the future changes are dependent on the model used. Suppressed vertical motion over the equatorial (northern) Indian Ocean caused by the vertically stabilized atmosphere under the global warming scenario is the source of the first (third) mode, together with the counter vertical motion anomaly over the equatorial (northern) Pacific. The aforementioned characteristics of the modes are essentially similar to those identified in the CMIP5 analysis, whereas the different sea surface temperature anomalies are related to the secondary structures of the modes. Some uncertainties in the future projections can be attributed to the systematic differences in the model climatology of the present-day precipitation, which determines the distribution of the suppressed vertical motion under the future warmer climate. [ABSTRACT FROM AUTHOR]

The monsoon development in the early rainy season in East Asia is analysed by the evolution of daily weather types (WTs). The WTs are classified by a k‐means clustering analysis based on 850 hPa winds from April 1 to July 31 in the 40‐year period of 1979–2018. Five WTs are identified, typifying the progression of weather regimes in the monsoonal evolution. WTs 1 and 2, with easterly winds in the South China Sea (SCS), occurs mostly in April and early May, corresponding to typical WTs before the SCS monsoon onset. In WT3, winds in the SCS turns westerly, and a rain band emerges in South China, extending east‐northeastward to the Pacific Ocean south of Japan, which signifies the May–June Mei‐yu in South China. Then, with the rain band moved to Yangtze River Valley (YRV) in WT4, this WT corresponds to the June–July Mei‐Yu in central and eastern China along the YRV. Finally, WT5 occurs more frequently towards the end of July, and corresponds to the post‐Mei‐Yu WT, indicating the ending of the early summer rainfall season in East Asia. The evolution of the WTs is gradual but intermittent, representing the weather‐within‐climate information. Each WT likely persists to itself. But WT1 and WT2 also progress to each other. The long persistence of WT3 and WT4 up to several weeks indicates the quasi‐stationary Mei‐Yu in South China and the YRV, respectively. The year‐to‐year variability of the WTs is also evident in the WTs. The El Niño–Southern Oscillation (ENSO) impact on the precipitation in the East Asian region is analysed for three types of ENSO: Eastern Pacific, Central Pacific, and mixed El Niño and La Niña. The seasonal mean precipitation anomalies can be interpreted by the frequencies of the daily WTs under different ENSO conditions. [ABSTRACT FROM AUTHOR]

Stalagmite is one kind of secondary carbonates formed in limestone caves (speleothem). After cave water droplets containing Ca2+ and H C O 3 − drip onto floor, carbonate in the water might become supersaturated due to CO2 degassing under certain conditions, resulting in the formation of stalagmite in a process year after year. Stalagmite is one of important geological archives for paleoclimate research. The advantages include wide spatial distribution, suitable for U-Th and U-Pb dating, enriched in climate proxies, continuity, long time span, comparability and lower sampling cost etc. These factors have propelled stalagmite paleoclimate research to the forefront of global paleoclimatology with an irreplaceable role. The stalagmite paleoclimate study started in the western countries, mainly in Europe and America in 1960s–1970s, while the relevant research in China was progressively developed in the 1980s–1990s after the Reform and Opening up. Although there was a huge gap between the overall research level in China and western countries, a solid research foundation, as well as a number of talent teams were established during the period. In the 21st century, starting from the publication of stalagmite records from Hulu Cave in Nanjing in 2001, the stalagmite paleoclimate research in China has ushered in a flourishing development and a real leap on the basis of international cooperation, resulting in significant international impacts. The landmark achievements, including establishment of the world's longest (640000 years) East Asian monsoon stalagmite record, as well as the longest Indian monsoon (280000 years), South American monsoon (250000 years), North American westerly climate (330000 years), Central Asian westerly climate (135000 years), and northwestern China westerly climate (500000 years), have laid a milestone in the paleoclimate study in these climate domains. Importantly, these stalagmite records have revealed the relationship of Asian monsoon variations with solar insolation climate change in polar regions, and the South American monsoon changes on orbital-suborbital timescales, which have provided new geological observations for the development of orbital-suborbital climate theory; elaborated coupling and differentiation relationships between the Asian monsoon and the westerly climate; reconstructed the history of Asian monsoon changes in the Holocene in detail, and thus the hydrological and climate variances behind Chinese and Indian civilization-cultural evolutions. Furthermore, a large number of high-resolution stalagmite records over the past 2000 years have been reconstructed, which are important for understanding short-term climate variability and magnitude, events, cycles, and thus the future climate projection. The achievements have also involved the improvements of a number of important techniques, such as U-Th dating method, the establishments of various hydroclimatic proxies, as well as the contributions to the reconstruction of the atmosphere 14C variation history over the past ∼54000 years. On the perspective of the future, the Chinese stalagmite community should continue to develop key techniques, further clarify the hydroclimatic significance of stalagmite proxies, impel the integration of related disciplines, and concentrate on key scientific issues in global climate change and major social demands. [ABSTRACT FROM AUTHOR]

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This work investigates the variability of extreme weather events (drought spells, DS15, and daily heavy rainfall, PR99) over East Asia. It particularly focuses on the large scale atmospheric circulation associated with high levels of the occurrence of these extreme events. Two observational datasets (APHRODITE and PERSIANN) are compared with two high-resolution global climate models (HiRAM and HadGEM3-GC2) and an ensemble of other lower resolution climate models from CMIP5. We first evaluate the performance of the high resolution models. They both exhibit good skill in reproducing extreme events, especially when compared with CMIP5 results. Significant differences exist between the two observational datasets, highlighting the difficulty of having a clear estimate of extreme events. The link between the variability of the extremes and the large scale circulation is investigated, on monthly and interannual timescales, using composite and correlation analyses. Both extreme indices DS15 and PR99 are significantly linked to the low level wind intensity over East Asia, i.e. the monsoon circulation. It is also found that DS15 events are strongly linked to the surface temperature over the Siberian region and to the land-sea pressure contrast, while PR99 events are linked to the sea surface temperature anomalies over the West North Pacific. These results illustrate the importance of the monsoon circulation on extremes over East Asia. The dependencies on of the surface temperature over the continent and the sea surface temperature raise the question as to what extent they could affect the occurrence of extremes over tropical regions in future projections. [ABSTRACT FROM AUTHOR]