In the context of China's dual carbon goal, emissions of air pollutants are expected to significantly decrease in the future. Thus, the direct climate effects of black carbon (BC) aerosols in East Asia are investigated under this goal using an updated regional climate and chemistry model. The simulated annual average BC concentration over East Asia is approximately 1.29 mu g/m(3) in the last decade. Compared to those in 2010-2020, both the BC column burden and instantaneous direct radiative forcing in East Asia decrease by more than 55% and 80%, respectively, in the carbon peak year (2030s) and the carbon neutrality year (2060s). Conversely, the BC effective radiative forcing (ERF) and regional climate responses to BC exhibit substantial nonlinearity to emission reduction, possibly resulting from different adjustments of thermal-dynamic fields and clouds from BC-radiation interactions. The regional mean BC ERF at the tropopause over East Asia is approximately +1.11 W/m(2) in 2010-2020 while negative in the 2060s. BC-radiation interactions in the present-day impose a significant annual mean cooling of -0.2 to -0.5 K in central China but warming +0.3 K in the Tibetan Plateau. As China's BC emissions decline, surface temperature responses show a mixed picture compared to 2010-2020, with more cooling in eastern China and Tibet of -0.2 to -0.3 K in the 2030s, but more warming in central China of approximately +0.3 K by the 2060s. The Indian BC might play a more important role in East Asian climate with reduction of BC emissions in China.

Aerosols in Southeast Asia (SEA) are entangled with complex land-sea-atmosphere-human interactions, and it is difficult for scientists to understand their dynamic behaviors. This study aims to provide an insightful understanding of aerosols across SEA with respect to their radiative properties using several lines of evidence obtained from remote sensing instruments, including those from onboard Earth observation satellites (MODIS/Terra and MODIS/Aqua, CALIOP/CALIPSO) and from ground-based observation (AERONET). The findings, obtained from cluster analysis of aerosol optical properties, showed seven aerosol types which were dominant across the country, exhibiting diverse radiative forcing potentials. The light-absorbing (prone to warm the atmosphere) aerosols were likely found in mainland SEA, both for background and high-aerosol events. The light-scattering aerosols were associated with aging processes and hygroscopic growth. The neutral potential, which comprised a mixture of oceanic and local anthropogenic aerosols, was predominant in background aerosols in insular SEA. Further studies should focus on carbonaceous aerosols (organic carbons, black carbon, and brown carbon), the aging processes, and the hygroscopic growth of these aerosols, since they play significant roles in the regional aerosol optical properties.

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.

A comprehensive study on classifying the aerosol types and absorbing aerosol types, and quantifying the effect of absorbing aerosols on aerosol optical and radiative properties using four years (2015-2016, 2018-2019) of high-quality Aerosol Robotic Network (AERONET) datasets over Kanpur (urban) and Gandhi College (rural) in the Indo-Gangetic Plain (IGP) region is conducted on a seasonal scale, for the first time. Biomass burning (BB), urban-industrial, and mixed aerosol types are always present, whereas dust aerosol and mostly dust absorbing aerosol types are only present in pre-monsoon and monsoon seasons. During winter and post-monsoon seasons, BB aerosols andmostly black carbon (MBC) absorbing aerosols dominate, and the contribution of aerosol optical depth (AOD) and single scattering albedo (SSA) corresponding to MBC to total AOD and SSA are higher. SSA for MBC varies over a broader range due to mixing of BC with water-soluble aerosols. During pre-monsoon and monsoon seasons, mixing of dust with anthropogenic aerosols increases the amount of mixed aerosol type. Surface cooling and atmospheric heating efficiency for mixed aerosols are higher than MBC and dust aerosols due to enhancement in aerosol absorption over both locations. Seasonal analysis of aerosol radiative properties showed that during winter and post-monsoon, MBC absorbing aerosols are the major contributor in controlling/influencing the total aerosol radiative forcing (ARF) and heating rate (HR). During the other seasons, each absorbing aerosol type significantly influences ARF depending on their AOD and SSA values. In addition to Kanpur and Gandhi College, data from seven other AERONET sites located at Karachi, Lahore, Jaipur, Lumbini, Pokhara, Bhola, and Dhaka in South Asia are analysed to conduct a regional-scale examination of aerosol optical parameters and radiative effects due to different absorbing aerosol types. As the aerosol characteristics and trends are similar over these sites, the findings from such a regional-scale analysis can be an appropriate representative for the South Asian region. The regional analysis revealed that the annual mean atmospheric ARF (ARF(ATM)) and ARF efficiency (ARFE(ATM)), and HR are higher for MBC, followed by mixed and MD aerosols over South Asia due to higher AOD, and higher absorbing efficiency of MBC aerosols. In comparison, mixed aerosols exhibit higher ARF(ATM) over East Asia. This quantification of absorbing aerosol types over a global aerosol hotspot will be useful for an accurate quantification of climate impacts of aerosols.

To establish the direct climatic and environmental effect of anthropogenic aerosols in East Asia in winter under external, internal, and partial internal mixing (EM, IM and PIM) states, a well-developed regional climate-chemical model RegCCMS is used by carrying out sensitive numerical simulations. Different aerosol mixing states yield different aerosol optical and radiative properties. The regional averaged EM aerosol single scattering albedo is approximately 1.4 times that of IM. The average aerosol effective radiative forcing in the atmosphere ranges from -0.35 to +1.40 W/m(2) with increasing internal mixed aerosols. Due to the absorption of black carbon aerosol, lower air temperatures are increased, which likely weakens the EAWM circulations and makes the atmospheric boundary more stable. Consequently, substantial accumulations of aerosols further appear in most regions of China. This type of interaction will be intensified when more aerosols are internally mixed. Overall, the aerosol mixing states may be important for regional air pollution and climate change assessments. The different aerosol mixing states in East Asia in winter will result in a variation from 0.04 to 0.11 K for the averaged lower air temperature anomaly and from approximately 0.45 to 2.98 mu g/m(3) for the aerosol loading anomaly, respectively, due to the different mixing aerosols.

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.

With global warming, the probability of summer compound hot and dry extreme (CHDE) days, which are higher risk compared with single-factor extreme events, increases in some regions. However, there have been few studies on the winter precursor signals of such events. In this study, we found that summer CHDEs have generally increased in the last 20 years, with the increases in the middle and lower reaches of the Yangtze River region and Southwest China being more than double those in other regions of China. The dominant mode of summer CHDEs in China is characterized by more hot-dry days in the Yangtze-Huaihe River Basin (YHRB). Importantly, we found that there is an obvious cross-seasonal relationship between the first mode of winter snow cover in the Northern Hemisphere (NH) and summer CHDEs in China. When the mode of winter snow cover in the NH is in a positive phase with a negative-phase Arctic Oscillation (AO), i.e., more snow cover in Europe, Northeast China, and the northern United States, and less snow cover in central Asia and the midlatitudes in winter, more CHDEs in China in the following summer. Compared with the signals from the AO, these signals from winter snow can be better stored and transmitted into summer through the snow, soil and ocean, inducing a northward shift of the upper-level westerly jet and strengthening of South Asia high. Through the strong dynamic forcing of negative vorticity advection with the change of westerly jet, the subsidence movement in the western Pacific subtropical high (WPSH) region is strengthened, resulting in the stable maintenance of the WPSH in the YHRB. Under the synergy of a remote mid- and high-latitude wave train in summer, which also relates closely to winter snow cover, more CHDEs ultimately occur in the YHRB of China.

Chiang Mai suffers from adverse haze associated with heavy biomass burning (BB) during almost every dry season (February to April). As an important source of light-absorbing carbonaceous aerosols (black carbon and brown carbon), BB can have strong radiative effects on local and regional climate. However, studies on characterizing the impacts of BB aerosols on climate in Chiang Mai are quite limited. In this study, we use a global chemical transport model (GEOS-Chem) coupled with the rapid radiative transfer model for GCMs (RRTMG) to estimate the radiative forcing (RF) of BB aerosols in Chiang Mai. Brown carbon (BrC) is included as an absorber and treated as an individual tracer in the model. To our best knowledge, this is the first study to estimate the BrC RF in Chiang Mai. As evaluated, our simulations that were assigned with medium- and high-absorbing kBrC (BrC imaginary refractive index) well reproduces the absorption coefficient of ambient BrC in Chiang Mai. Based on our estimations, 33-40% of total carbonaceous aerosol absorption at 440 nm is attributed to BrC and 60-67% to BC during dry season. As estimated, BrC contributes 14 +/- 3% to the instantaneous RF of total carbonaceous aerosol (IRFCAs) at the top of atmosphere (TOA) and 16 +/- 3% to IRFCAs at surface. Moreover, including BrC in model strengthens (reduces) the surface (TOA) cooling effect of total organic carbon by 9 +/- 5% (9 +/- 3%), indicating the warming effect of BrC in the atmosphere in Chiang Mai.