Knowledge of the paleoclimatic record of the northeastern Tibetan Plateau (NETP) can potentially improve our understanding of the evolution of the Asian summer monsoon (ASM). However, the history of climate change and inferred spatial extent of the ASM on the NETP since the last deglaciation remain unclear. Here, we use several environmental proxies from the sediments of Hala Lake (beyond the modern limit of ASM), including chironomids, loss-on-ignition, grain size and element data, to explore the climatic history of the NETP and the northern boundary of the ASM since the last deglaciation. The results document a series of climatic events during the deglaciation, including Heinrich Event 1, the Bolling-Allerod interstadial and the Younger Dryas event. The records also reveal the timing of the megathermal and precipitation maximum, the lake-level maximum, and strongest chemical weathering, which occurred during similar to 10-7 ka. The inferred precipitation maximum during the early Holocene in the Hala Lake basin, which can be verified by the simulated precipitation change, is consistent with that in typical Indian summer monsoon (ISM) regions, suggesting that the ISM has penetrated into Hala Lake basin at that time. The monsoon-dominated climate in the Hala Lake basin during the early Holocene and the westerlies-dominated climate in the arid central Asia indicate that the maximum areal extent of the ASM on the NETP since the last deglaciation lay to the northwest of Hala Lake basin. In combination with other published records, the northernmost boundary of the ASM over China since the last deglaciation has been tentatively delineated, to shed some lights on this long-standing debate.

The northernmost margin of the East Asian summer monsoon (NMEASM) is the northernmost position that the East Asia summer monsoon (EASM) can reach. NMEASM has obvious multi-scale variability, and well reflects the wet/dry climate variability in northern China. Predicting the location change of the NMEASM is important for understanding future East Asian climate change. However, the variability of the NMEASM has not been studied extensively, and its underlying mechanisms have not been clarified. To explore the movement of the NMEASM and its causes, we use reanalysis datasets to evaluate the NMEASM index from 1979 to 2018. The NMEASM indicates a decreasing trend over 40 years and a significant abrupt point in 2000, which is positively correlated with the Tibetan Plateau snow cover before 2000 and the Siberian snow cover after 2000 in spring. The decreased Siberian snow cover increases the soil temperature and decreases the atmospheric baroclinicity over Mongolia and northern China after 2000. The decreased atmospheric baroclinicity induces the dipole mode of anticyclonic anomaly over Mongolia and northern China and the cyclonic anomaly over the Sea of Japan by modulating the wave activity flux (WAF). The WAF's southeastward propagation strengthens the anticyclonic anomaly over Mongolia and northern China and the cyclonic anomaly over the Sea of Japan, which weakens the upward movement and water vapor transport, respectively. Hence, the decreased Siberian snow cover in spring modulates the precipitation over Mongolia and northern China and the southward movement of NMEASM by turbulent westerly circulation.

Aerosol mixtures, which are still unclear in current knowledge, may cause large uncertainties in aerosol climate effect assessments. To better understand this research gap, a well-developed online coupled regional climate-chemistry model is employed here to investigate the influences of different aerosol mixing states on the direct interactions between aerosols and the East Asian summer monsoon (EASM). The results show that anthropogenic aerosols have high-level loadings with heterogeneous spatial distributions in East Asia. Black carbon aerosol loading accounts for more than 13% of the totals in this region in summer. Thus, different aerosol mixing states cause very different aerosol single scattering albedos, with a variation of 0.27 in East Asia in summer. Consequently, the sign of the aerosol instantaneous direct radiative forcing at the top of the atmosphere is changed, varying from - 0.95 to + 1.50 W/m(2) with increasing internal mixing aerosols. The influence of aerosol mixtures on regional climate responses seems to be weaker. The EASM circulation can be enhanced due to the warming effect of anthropogenic aerosols in the lower atmosphere, which further induces considerable aerosol accumulation associated with dynamic field anomaly, decrease in rainfall and so on, despite aerosol mixtures. However, this interaction between aerosols and the EASM will become more obvious if the aerosols are more mixed internally. Additionally, the differences in aerosol-induced EASM anomalies during the strongest and weakest monsoon index years are highly determined by the aerosol mixing states. The results here may further help us better address the environmental and climate change issues in East Asia.

Aeolian landscapes dominate the semiarid dune fields across the Asian summer monsoonal boundary (ASMB) of northern China, where the widespread palaeosols are usually regarded as indicators of enhanced monsoonal precipitation (moisture) during the Late Quaternary. However, the processes of palaeosol development, and their response to climate change, remain controversial due to the complex land-atmosphere interactions within different bioclimatic zones. Here, we review the patterns of palaeosol development, precipitation/moisture (P/ M) evolution, and lake level fluctuations across different sub-regions of the ASMB. With the aid of typical temperature and vegetation records, we qualitatively and quantitatively distinguish the contributions of different climatic factors to palaeosol development since 20 ka (1 ka = 1000 cal yr BP) and elucidate the underlying mechanisms. Our results indicate an asynchronous pattern of palaeosol development, with optimum develop-ment during 10-4, 8-4, and 6-2 ka in northeastern (NE) China, north central (NC) China, and on the NE Qinghai -Tibetan Plateau (QTP), respectively. This implies a transmeridional asynchronous pattern of palaeosol devel-opment on the scale of the ASMB. Our qualitative and quantitative analysis of the contributions of climatic variables elucidates the various relationships between palaeosol development and the climatic background across different sub-regions of the ASMB. The results demonstrate that temperature and precipitation are the dominant factors for palaeosol development in NE and NC China, respectively; whereas effective moisture, rather than temperature and precipitation alone, controls palaeosol development on the NE QTP, demonstrating different pedogenic responses against the same overall climatic background. These mechanisms are supported by the results of multiple studies of Holocene vegetation evolution and the associated climatic conditions. We conclude that the asynchronous pattern of palaeosol development across the ASMB was caused by variations in different dominant climatic factors, highlighting the diverse and complex interactions of climate change and Earth surface processes, even within the relatively uniform climatic environment of semiarid northern China. Our findings emphasize the differing responses of palaeosol development to regional climate change and provide new insights into the interactions of the land-atmosphere system in the critical zone of northern China.

Opposite anthropogenic aerosol emission trends in Asia can lead to different responses of the climate. Here, we examined the responses of the East Asian summer monsoon (EASM) to changes in Asian anthropogenic aerosol emissions during 2006-2014 using a global aerosol/atmospheric chemistry-climate coupled model (BCC_AGCM2.0_CUACE/Aero) with two sets of emission inventories: the Community Emissions Data System (CEDS) inventory adopted by the Coupled Model Intercomparison Project Phase 6 (CMIP6) and the inventory developed at Peking University (PKU). The changes in Asian anthropogenic aerosol emissions during 2006-2014 between the two inventories were remarkably different, particularly in eastern China where completely opposite trends were observed (i.e., increase in the CEDS inventory, but significant reduction in the PKU inventory). The perturbation simulations with the Asian anthropogenic aerosol forcing from the two inventories showed opposite changes in aerosol optical depth, aerosol effective radiative forcing, cloud liquid water path, and total cloud cover in eastern China. The simulated 'dipole-type' changes (i.e., increase in India but decrease in China) in Asian aerosols and the resulting changes in local radiation budget under the PKU inventory were consistent with the corresponding observations. The summer surface temperatures over eastern China decreased by 0-0.4 K because of the Asian anthropogenic aerosol forcing under the CEDS inventory, while they increased by 0.1-0.8 K under the PKU inventory. The weakening of the EASM index caused by the Asian aerosol forcing under the PKU inventory was twofold greater than that under the CEDS inventory (-0.4 vs. -0.2). The Asian 'dipole-type' aerosol forcing contributed to the observed summer 'southern drought and northern flood' phenomenon in eastern China during 2006-2014. The slow ocean-mediated response to the regional 'dipole-type' aerosol forcing dominated the weakening of the EASM circulation and the precipitation changes in eastern China in the total response. This study further confirms that the biases in anthropogenic aerosol emissions over Asia can affect the CMIP6-based regional climate attribution.

The response of vegetation to past global warming, as revealed by geological records, can provide insights into future changes. We used pollen records to reconstruct spatial changes in the boundary between steppe and forest/forest-steppe for the Last Glacial Maximum (LGM), mid-Holocene, Last Interglacial (LIG), and mid-Pliocene, representing major changes in global temperature. The results showed that in the region east of 110 degrees E, the trend of the boundary between steppe and forest/forest-steppe rotated anticlockwise by around 30 degrees, 5 degrees and 10 degrees, during the warm periods of the mid-Holocene, LIG, and mid-Pliocene, relative to the LGM, mid-Holocene, and LIG, respectively. However, in the region west of 110 degrees E, the boundary remained stationary during the mid-Holocene compared with the LGM, while it shifted northward during the LIG relative to the mid-Holocene, and it shifted southward during the mid-Pliocene relative to the LIG. Overall, our results indicate an enhanced east-west climatic contrast in northern China under past global warming. Climate simulation results showed that the warming-induced northward shift and westward extension of the western Pacific subtropical high promoted the northwestward displacement of the East-Asian monsoon rainfall belt. This suggests that in the future, under a warmer climate, the eastern region of northern China will become wetter, and that the extent of sandy desert will decrease.

Characterizing the vertical distribution of aerosol optical properties is crucial to reduce the uncertainty in quantifying the radiative forcing and climate effects of aerosols. The analysis of four-year (2007-2010) Cloud-Aerosol Lidar and Infrared Pathfinder Satellite Observation (CALIPSO) lidar measurements revealed the existence of tropospheric aerosol layers associated with the Asian summer monsoon. The measurements of five typical aerosol optical and microphysical parameters were used to explore the properties, spatial/vertical distributions, annual evolution of tropopause aerosols over the South Asia region. Results extracted from various latitude-height and longitude-height cross sections of aerosol extinction coefficient at 532 and 1064 nm, backscatter coefficient at 532 nm, and depolarization ratio at 532 nm demonstrated that a large amount of aerosols vertically extended up to the tropopause (12 km) during the monsoon season over the north Arabian Sea, India, north Bay of Bengal, and equatorial Indian Ocean, finally reaching the southeast of the Tibetan Plateau. Convective transport associated with Asian summer monsoon is an important factor controlling the vertical distribution of tropopause aerosols. The evolution of aerosol scattering ratio at 532 nm indicated that from equatorial Indian Ocean to South Asia, there exists an upward tilting and ascending structure of the aerosols layer during the monsoon season, which typically indicates enhanced aerosols over the Asian monsoon region. Information on aerosol size distribution and detailed composition are needed for better understanding the nature and origin of this aerosol layer. Enhancement of the tropopause aerosols should be considered in the future studies in evaluating the regional or global climate systems. Further satellite observations of aerosols and in-situ observations are also urgently needed to diagnose this aerosol layer, which likely originate from anthropogenic emissions. (C) 2019 Elsevier Ltd. All rights reserved.

The spatial distribution, radiative forcing, and climatic effects of tropospheric ozone in China during summer were investigated by using the regional climate model RegCM4. The results revealed that the tropospheric ozone column concentration was high in East China, Central China, North China, and the Sichuan basin during summer. The increase in tropospheric ozone levels since the industrialization era produced clear-sky shortwave and clear-sky longwave radiative forcing of 0.18 and 0.71 W m(-2), respectively, which increased the average surface air temperature by 0.06 K and the average precipitation by 0.22 mm day(-1) over eastern China during summer. In addition, tropospheric ozone increased the land-sea thermal contrast, leading to an enhancement of East Asian summer monsoon circulation over southern China and a weakening over northern China. The notable increase in surface air temperature in northwestern China, East China, and North China could be attributed to the absorption of longwave radiation by ozone, negative cloud amount anomaly, and corresponding positive shortwave radiation anomaly. There was a substantial increase in precipitation in the middle and lower reaches of the Yangtze River. It was related to the enhanced upward motion and the increased water vapor brought by strengthened southerly winds in the lower troposphere.

RegCM4.3, a high-resolution regional climate model, which includes five kinds of aerosols (dust, sea salt, sulfate, black carbon and organic carbon), is employed to simulate the East Asian summer monsoon (EASM) from 1995 to 2010 and the simulation data are used to study the possible impact of natural and anthropogenic aerosols on EASM. The results show that the regional climate model can well simulate the EASM and the spatial and temporal distribution of aerosols. The EASM index is reduced by about 5% by the natural and anthropogenic aerosols and the monsoon onset time is also delayed by about a pentad except for Southeast China. The aerosols heat the middle atmosphere through absorbing solar radiation and the air column expands in Southeast China and its offshore areas. As a result, the geopotential height decreases and a cyclonic circulation anomaly is generated in the lower atmosphere. Northerly wind located in the west of cyclonic circulation weakens the low-level southerly wind in the EASM region. Negative surface radiative forcing due to aerosols causes downward motion and an indirect meridional circulation is formed with the low-level northerly wind and high-level southerly wind anomaly in the north of 25 degrees N in the monsoon area, which weakens the vertical circulation of EASM. The summer precipitation of the monsoon region is significantly reduced, especially in North and Southwest China where the value of moisture flux divergence increases.

We quantified the impacts of variations in meteorological parameters and emissions on decadal, interannual, and seasonal variations of atmospheric black carbon (BC) in the Tibetan Plateau for 1980-2010 using a global 3-dimensional chemical transport model driven by the Modern Era Retrospective-analysis for Research and Applications (MERRA) meteorological fields. From 1980 to 2010, simulated surface BC concentrations and all-sky direct radiative forcing at the top of the atmosphere due to atmospheric BC increased by 0.15 mu g m(-3) (63%) and by 0.23 W m(-2) (62%), respectively, averaged over the Tibetan Plateau (75-105 degrees E, 25-40 degrees N). Simulated annual mean surface BC concentrations were in the range of 0.24-0.40 mu g m(-3) averaged over the plateau for 1980-2010, with the decadal trends of 0.13 mu g m(-3) per decade in the 1980s and 0.08 in the 2000s. The interannual variations were -5.4% to 7.0% for deviation from the mean, 0.0062 mu g m(-3) for mean absolute deviation, and 2.5% for absolute percent departure from the mean. Model sensitivity simulations indicated that the decadal trends of surface BC concentrations were mainly driven by changes in emissions, while the interannual variations were dependent on variations of both meteorological parameters and emissions. Meteorological parameters played a crucial role in driving the interannual variations of BC especially in the monsoon season.