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As large-scale ocean circulation is a key regulator in the redistribution of oceanic energy, evaluating the multi-decadal trends in the western Pacific Ocean circulation under global warming is essential for not only understanding the basic physical processes but also predicting future climate change in the western Pacific. Employing the hydrological observations of World Ocean Atlas 2018 (WOA18) from 1955 to 2017, this study calculated the geostrophic currents, volume transport and multi-decadal trends for the North Equatorial Current (NEC), the North Equatorial Countercurrent (NECC), the Mindanao Current (MC), the Kuroshio Current (KC) in the origin and the New Guinea Coastal Undercurrent (NGCUC) within tropical western Pacific Ocean over multi-decades. Furthermore, this study examined the contributions of temperature and salinity variations. The results showed significant strengthening trends in NEC, MC and NGCUC over the past six decades, which is mainly contributed by temperature variations and consistent with the tendency in the dynamic height pattern. Zonal wind stress averaged over the western Pacific Ocean in the same latitude of each current represents the decadal variation and multi-decadal trends in corresponding ocean currents, indicating that the trade wind forcing plays an important role in the decadal trend in the tropical western Pacific circulation. Uncertainties in the observed hydrological data and trends in the currents over the tropical western Pacific are also discussed. Given that the WOA18 dataset covers most of the historical hydrological sampling data for the tropical western Pacific, this paper provides important observational information on the multi-decadal trend of the large-scale ocean circulation in the western Pacific. [ABSTRACT FROM AUTHOR]

This paper reviews the three-pattern decomposition of global atmospheric circulation (3P-DGAC) developed in recent years, including the decomposition model and the dynamical equations of global horizontal, meridional, and zonal circulations. Compared with the traditional two-dimensional (2D) circulation decomposition method, the 3P-DGAC can effectively decompose the actual vertical vorticity into two components that are caused by the horizontal circulation and convergent/divergent movement (associated with the meridional and zonal circulations). It also decomposes the vertical velocity into the components of the meridional vertical circulation and the zonal vertical circulation, thus providing a new method to study the dynamical influences of convergent/divergent motions on the evolution of actual vertical vorticity and an accurate description of local vertical circulations. The 3P-DGAC is a three-dimensional (3D) circulation decomposition method based on the main characteristics of the actual atmospheric movements. The horizontal, meridional, and zonal circulations after the 3P-DGAC are the global generalization of Rossby waves in the middle-high latitudes and Hadley and Walker circulations in low latitudes. Therefore, the three-pattern decomposition model and its dynamical equations provide novel theoretical tools for studying complex interactions between middle-high and low latitude circulations as well as the physical mechanisms of the abnormal evolution of large-scale atmospheric circulations under the background of global warming. [ABSTRACT FROM AUTHOR]

The traditional dynamical downscaling (TDD) method employs continuous integration of regional climate models (RCM) with the general circulation model (GCM) providing the initial and lateral boundary conditions. Dynamical downscaling simulations are constrained by physical principles and can generate a full set of climate information, providing one of the important approaches to projecting fine spatial-scale future climate information. However, the systematic biases of climate models often degrade the TDD simulations and hinder the application of dynamical downscaling in the climate-change related studies. New methods developed over past decades improve the performance of dynamical downscaling simulations. These methods can be divided into four groups: the TDD method, the pseudo global warming method, dynamical downscaling with GCM bias corrections, and dynamical downscaling with both GCM and RCM bias corrections. These dynamical downscaling methods are reviewed and compared in this paper. The merits and limitations of each dynamical downscaling method are also discussed. In addition, the challenges and potential directions in progressing dynamical downscaling methods are stated. [ABSTRACT FROM AUTHOR]

Air temperature feedback results from the thermal-radiative coupling between the atmosphere and the surface and plays an important role in surface energy balance. This paper reveals the contribution of air temperature feedback to the global warming from 1980 to 2000. The air temperature feedback kernel, evaluated using the ERA-Interim reanalysis data, is used to discuss the physical mechanism for air temperature feedback, the dependency of the strength of air temperature feedback on the climatological spatial distributions of air temperature, water vapor and cloud content, and the contributions of air temperature feedback to rapid global warming. The coupling between temperature feedback and each of the external forcings and individual feedback processes will amplify the anomaly of direct energy flux convergence at the surface induced by the external forcings and individual processes. The air temperature feedback amplifies the initial surface warming due to the increase in CO2 concentration, ice and snow melting, increase in water vapor, and change in ocean heat storage. It also amplifies the surface warming due to the longwave radiaitve forcing associated with the increase in cloud cover, which acts to suppress the cooling of the shortwave effect of cloud forcing. Overall, temperature feedback plays an important role in the global warming from 1980 to 2000, as the net positive contribution to the perturbation of global mean energy flux at the surface from the air temperature feedback is larger than the net negative contribution from external forcing and all non-temperature feedbacks. [ABSTRACT FROM AUTHOR]

The two leading modes of winter surface air temperature (SAT) over China during 1961–2017 are a spatially consistent pattern and a north-south dipole pattern. Based on the two leading modes, the characteristics of the extreme cold and warm days in the two patterns, defined by the standard deviation larger than 1.28 or smaller than −1.28 in the time series of the two leading modes, are analyzed. With the increase of winter SAT during 1961–2017, the number of spatially consistent extreme cold days decreased and their occurrence was restricted to late December to early January, whereas the number of spatially consistent extreme warm days increased significantly in January and February. Global warming is associated with an increase in the spatially consistent extreme warm days and a decrease in spatially consistent extreme cold days, but has little relation to the sum of extreme cold and warm days of either the spatially consistent or north-south dipole pattern. The Siberian High (SH) is the main factor controlling the sum of spatially consistent extreme warm and cold days. The strong (weak) SH before (after) the 1990s corresponds to an increase (decrease) in the sum of the spatially consistent extreme warm and cold days. The occurrences of extreme south-cold-north-warm and extreme south-warm-north-cold days are related to the north-south difference of the SH. When the center of the SH is in mid-high latitudes, the extreme south-warm-north-cold (south-cold-north-warm) days occur more (less) often. During the winters of 1961–2017, the total number of extreme cold and warm days of the north-south dipole pattern changes negligibly. The North Atlantic meridional overturning circulation (AMOC) may be the main factor affecting the sum of the extreme cold and warm days of the two types of SAT pattern in China. [ABSTRACT FROM AUTHOR]

The Fourth Assessment Report (AR4) of the Intergovernmental Panel of Climate Change (IPCC) concluded that the climate projection using climate models that took account of both human and natural factors provided credible quantitative estimates of future climate change; however, the mismatches between the IPCC AR4 model ensembles and the observations, especially the multi-decadal variability (MDV), have cast shadows on the confidence of the model-based decadal projections of future climate. This paper reports an evaluation of many individual runs of AR4 models in the simulation of past global mean temperature. We find that most of the individual model runs fail to reproduce the MDV of past climate, which may have led to the overestimation of the projection of global warming for the next 40 years or so. Based on such an evaluation, we propose an alternative approach, in which the MDV signal is taken into account, to project the global mean temperature for the next 40 years and obtain that the global warming during 2011-2050 could be much smaller than the AR4 projection. [ABSTRACT FROM AUTHOR]

The estimation of the global warming mitigation potential in terrestrial ecosystems is of great importance for decision makers to adopt measures to increase soil organic carbon (SOC) as well as to reduce greenhouse gas (GHGs) emissions. In this paper, we compiled data published in peer-reviewed journals, and conducted a holistic analysis of the effects of organic matter amendment on soil organic carbon sequestration, methane (CH) and nitrous oxide (NO) emissions in paddy and upland systems. Results showed that organic matter amendment increased soil organic carbon content, and apparent conversion rate of organic matter carbon to soil organic carbon in paddies was constant, while that in uplands decreased along with amendment years at 25 years time scale. Organic matter amendment during the rice season led to large CH-C emissions, e.g on average 99.5 g CH-C per kg organic carbon input under intermittent flood conditions, and 191.7 g CH-C per kg organic carbon input under continuous flood conditions, respectively. By alteration of organic matter amendment from rice season to off-rice upland crop season, estimated CH-C emissions in China could be cut by 3.5 Tg yr, accounting for 63% of current CH-C emissions (5.5 Tg). If organic matter amendment percentage was increased from current 30% to future 50% of organic matter production and by alteration of organic matter amendment from rice season to off-rice upland crop season, the equivalent CO-C mitigation potential in farmland of China would be 49.2 Tg yr at the 10th year organic matter amendment and 36.0 Tg yr at the 30th year amendment. These findings are important not only for China but also for the other rice production countries to increase farmland global warming mitigation. [ABSTRACT FROM AUTHOR]

The climate warming is mainly due to the increase in concentrations of anthropogenic greenhouse gases, of which CO is the most important one responsible for radiative forcing of the climate. In order to reduce the great estimation uncertainty of atmospheric CO concentrations, several CO-related satellites have been successfully launched and many future greenhouse gas monitoring missions are planned. In this paper, we review the development of CO retrieval algorithms, spatial interpolation methods and ground observations. The main findings include: 1) current CO retrieval algorithms only partially account for atmospheric scattering effects; 2) the accurate estimation of the vertical profile of greenhouse gas concentrations is a long-term challenge for remote sensing techniques; 3) ground-based observations are too sparse to accurately infer CO concentrations on regional scales; and 4) accuracy is the primary challenge of satellite estimation of CO concentrations. These findings, taken as a whole, point to the need to develop a high accuracy method for simulation of carbon sources and sinks on the basis of the fundamental theorem of Earth's surface modelling, which is able to efficiently fuse space- and ground-based measurements on the one hand and work with atmospheric transport models on the other hand. [ABSTRACT FROM AUTHOR]

The question of whether or not global warming has paused since more than ten years ago, namely 'warming hiatus', has attracted the attention of climate science community including the IPCC. Some authors have attributed the 'warming hiatus' to the internal changes in the climate system, i.e., the recombination of ocean-atmosphere circulations. Therefore, it is necessary to propose higher requirements on reconstructing circulation background of climate change for the past millennium. However, the analyses of changes in atmospheric circulation over the last millennium as well as the conclusions of related regional climate patterns are so widely different and contradictory, bringing uncertainties to our understanding of regional even global climate change to a great extent. On the other hand, in the last 10 years the high-precision U/Th-dated stalagmite oxygen isotope ratio ( δO) sequences provided an accurate chronological frame for the paleoclimate study of the middle and late Pleistocene, in which all authors from China took the Chinese stalagmite δO as the summer monsoon index without exception. However, this point of view misleads the climate scientists into thinking that the stalagmite δO can be as the proxy of precipitation amount. Nevertheless, it is well known that all of these records have a lot in common in the low frequency trend. However, most sequences cannot be calibrated by instrumental precipitation records, and thus the uncertainty of the climate research framework of China and even of the world has increased. Therefore, it is imperative for climatology to clarify the origin of contradiction and to reduce the uncertainty as early as possible. On the basis of analyzing the significance of stalagmite δO in the monsoon regions of China, the author tries to propose a new circulation proxy in this paper: integrating the Chinese stalagmite oxygen isotope sequence to reconstruct the tropical Pacific sea surface temperature gradient, i.e., the large-scale ENSO-like state over the past millennium. Furthermore, the author speculates that it was warm in the modern times and the Medieval Period, but the circulation recombination was different in both periods. And this inference could be supported by the longer record since Last Glacial Maximum. In other words, the attribution analysis of the identical low-frequency trends of Chinese stalagmite δO on a large scale shows that the ENSO-like state controls the climate change in the monsoon regions of China at different time scales (from interannual to century or even longer time scales). Wherein the important connection of circulations is the western Pacific subtropical high (WPSH), that is to say, besides the interannual and decadal time scales, the WPSH would possess the circulation mode on longer timescales. For example, we may discuss the change of the WPSH in the whole Holocene epoch, i.e., the half precession period. These discussions could make sense to the study of not only the paleoclimate but also the modern climate. [ABSTRACT FROM AUTHOR]

Global climate change and its possible ecological consequences have become the focused issue (IPCC, 2007; Mann et al., 2008; Ding et al., 2009). The Holocene contains the analogous characteristic of future climatic change and the continuous agriculture activity, providing the ideal “similar pattern” for studying the climate change and human adaption and impact in the future. Based on the recent studies of stalagmite, ice core, ocean, and lake etc., the paper introduces the new progress in the Holocene climate and agriculture research in China as follows: (1) Discuss the variability, amplitude, and unstable characteristic of climate, as well as the abrupt events and mechanisms of climate. (2) Analyze the botanical index records for studying the early agriculture. (3) Review the agricultural origin, expanding, and development. (4) Reveal the style and intensity of early agriculture and understand the agricultural impact and adaption to the environmental changes. (5) Introduce ongoing research projects in China and emphasize the significance of increasing the dating precision and the indicative effectiveness of proxies. (6) Realize how the ecosystem and environmental factors respond to the increasing temperature process, understand how the human adapt to the rapid climate change, and provide the scientific basis for assessing the effects of climate change and the human adaption in the future. [ABSTRACT FROM AUTHOR]

This paper reviews both the recent and longer-term (Holocene) ecological history of coral reefs in the South China Sea (SCS). (1) Local ecological monitoring since the 1960s shows that the coral reefs in the South China Sea have declined dramatically, reflecting the rapid decrease of living coral cover and the great loss of symbiotic zooxanthellae. Collectively, this has led to a significant decrease of annual CaCO production. Heavy anthropogenic activities and global warming are recognized as major triggers of the observed coral reef degradation. Observations show that the modern coral reefs in the SCS are a source of atmospheric CO in summer. (2) Coral reefs of the SCS have been widely used to reveal longer-term environmental variations, including Holocene high-resolution sea surface temperature (SST) and abrupt climate events, millennial-scale El Niño variations, millennial- and centennial-scale sea level oscillations, strong and cyclic storm activities, East Asian monsoon intensities, variation in seawater pH, and recent seawater pollution. (3) Coral reefs of the southern SCS have experienced repeated episodes of bleaching over the last 200 years due to high SST and intense El Niño events; coral reefs of the northern SCS suffered high levels of mortality during several abrupt winter cold-water bleaching events during the middle Holocene warm period. On average, recovery after the middle Holocene cold-bleaching took 20-30 years; recovery following other middle Holocene environmental stresses took approximately 10-20 years. Such findings have significantly contributed to the understanding of the present ecological pressures faced by the coral reefs in the SCS, the histories of Holocene climate/environment changes, and the long-term models of coral reef responses to various past environmental changes. [ABSTRACT FROM AUTHOR]

The Holocene, the most recent interglacial, provides an important time window for evaluating current global warming and predicting future temperature changes. With the development of new temperature proxies and improvements in climate models, significant progress has been made in understanding Holocene temperature changes. However, a major debate persists about whether global temperatures during the Holocene followed a pattern of gradual warming from the end of the Last Glacial Maximum, which culminated in a temperature maximum in the early to middle Holocene, followed by gradual cooling in the late Holocene (the thermal maximum mode); or whether there was a continuous warming trend that continued to the present day (the continuous warming mode). Significant discrepancies exist between different proxy records as well as between proxy records and models, which have resulted in the "Holocene temperature conundrum" that has challenged paleoclimatologists for the past decade. Here, we summarize the progress made to date in the study of Holocene temperature change via proxy reconstructions, climate model simulations, and paleoclimate data assimilation. We emphasize that the current research has limitations in terms of the multiplicity and seasonality of proxy records, the spatial heterogeneity of temperature records, and the incorporation of feedback processes (e.g., vegetation, cloud-radiation feedback) in climate models. These limitations have hindered a comprehensive understanding of the processes and mechanisms of Holocene temperature changes. To solve the "Holocene temperature conundrum", it is necessary to strengthen theoretical research on climate proxies from the perspective of the underlying processes and mechanisms, elucidate the seasonal response of various temperature proxies, emphasize regional differences in temperature changes, and expand quantitative temperature reconstructions to areas with limited records. However, it is also necessary to improve the simulation performance of complex feedback processes in climate models, reduce simulation errors, and advance the research on data assimilation of Holocene continental temperature records, which may ultimately lead to the optimal integration of paleoclimate records and simulations. [ABSTRACT FROM AUTHOR]

Since Shi et al. proposed that the climate in the drylands of Northwest China experienced a significant transition from a "warming and drying" trend to a "warming and wetting" trend in the 1980s, researchers have conducted numerous studies on the variations in precipitation and humidity in the region and even in arid Central Asia. In particular, the process of the "warming and wetting" trend by using obtained measurement data received much attention. However, there remain uncertainties about whether the "warming and wetting" trend has paused and what its future variations may be. In this study, we examined the spatiotemporal variations in temperature, precipitation, the aridity index (AI), vegetation, and runoff during 1950–2019. The results showed that the climate in the drylands of Northwest China and the northern Tibetan Plateau is persistently warming and wetting since the 1980s, with an acceleration since the 1990s. The precipitation/humidity variations in North China, which are mainly influenced by summer monsoon, are generally opposite to those in the drylands of Northwest China. This reverse change is mainly controlled by an anomalous anticyclone over Mongolia, which leads to an anomalous easterly wind, reduced water vapor output, and increased precipitation in the drylands of Northwest China. While it also causes an anomalous descending motion, increased water vapor divergence, and decreased precipitation in North China. Precipitation is the primary controlling factor of humidity, which ultimately forms the spatiotemporal pattern of the "westerlies-dominated climatic regime" of antiphase precipitation/humidity variations between the drylands of Northwest China and monsoonal region of North China. The primary reasons behind the debate of the "warming and wetting" trend in Northwest China were due to the use of different time series lengths, regional ranges, and humidity indices in previous analyses. Since the EC-Earth3 has a good performance for simulating precipitation and humidity in Northwest and North China. By using its simulated results, we found a wetting trend in the drylands of Northwest China under low emission scenarios, but the climate will gradually transition to a "warming and drying" trend as emissions increase. This study suggests that moderate warming can be beneficial for improving the ecological environment in the drylands of Northwest China, while precipitation and humidity in monsoon-dominated North China will persistently increase under scenarios of increased emissions. [ABSTRACT FROM AUTHOR]

The Marine Isotope Stage (MIS5e) is characterized by a warmer climate than that of the pre-industrial period, and serves as an analog for the Current Warm Period (CWP). However, uncertainties persist regarding its climatic stability. Here, we retrieved a stalagmite (WXB075) from Wanxiang Cave in the eastern Qinghai-Tibetan Plateau, and employed absolute 230Th dating and relative annual layer data to establish a high-precision chronological framework for reconstructing the history of the Asian summer monsoon (ASM) and environmental evolution during early MIS5e with multiple proxies. The findings indicate that the annually laminated stalagmite was formed during Cooling Event 27 (C27). The deposition of WXB075 experienced a hiatus (∼125.58 ka BP) due to a significant cooling event in the North Atlantic, which may be linked to the unstable climate in the Northern Hemisphere. Additionally, the impact of meltwater discharge in high northern latitudes results in a two-phase evolution of the ASM, i.e., an initial weaker stage followed by a gradual increase (with the exception of deposition hiatus). The climatic instability of ASM is generally characterized by a quasi-60 year cycle that affects vegetation conditions, biological productivity, and karst hydroclimate dynamics. However, the increase in meltwater and decrease in temperature in the Northern Hemisphere have led to a weakened ASM and subsequent reduction in precipitation. Consequently, vegetation degradation above the cave has occurred along with a slowdown of karst hydroclimate. The vegetation conditions, organic matter content, and wet/drought of the karst hydroclimate were affected by both the large-scale monsoon circulation and local environment during extreme weakening (strengthening) of the monsoon when high-frequency climatic events of ASM occurred. A comparison of δ18O records between early MIS5e and the past 2000 years reveals that the climate during early MIS5e differed significantly from that of CWP, Medieval Warm Period (MWP), and Dark Age Cold Period (DACP) but was similar to Little Ice Age (LIA). Comparison with other geological records from the Northern Hemisphere indicates that climate instability was a widespread phenomenon during MIS5e. The power spectrum analysis of WXB075 δ18O reveals significant quasi-60 and 35 a cycles during the early MIS5e, which is consistent with the Atlantic Multidecadal Oscillation (AMO). The comprehensive results demonstrate that the ASM in the early MIS5e was closely linked to solar activity, Intertropical Convergence Zone (ITCZ) position, and Atlantic Meridional Overturning Circulation (AMOC). [ABSTRACT FROM AUTHOR]

Global warming has altered the thermodynamic and dynamic environments of climate systems, affecting the biogeochemical processes between the geosphere and atmosphere, which has significant impacts on precipitation extremes and the terrestrial carbon budget of ecosystems. Existing studies have reported a hook structure for precipitation extreme-temperature relationships but have rarely examined the underlying physical mechanisms. Previous studies have also failed to quantify the impact of precipitation on ecosystem productivity, hindering the assessment of future extreme climatic hazards and potential ecosystem risks. To reveal the thermodynamic driving mechanisms for the formation of global precipitation extremes and ecohydrological effects, this study utilizes over ten multisource datasets (i.e., satellite, reanalysis, climate model, land surface model, machine learning reconstruction, and flux tower measurements). We first assess the response of water-heat-carbon flux to precipitation extremes and explain the underlying physical mechanisms behind the hook structures in terms of atmospheric thermodynamics and dynamics. Based on outputs from five global climate models (GCMs) under ISIMIP3b, we project future changes in the hook structures as well as their impacts on precipitation extremes. Finally, we discuss the impact of precipitation on the terrestrial carbon budget by using outputs from the CLM4.5 model. The results show that precipitation extremes are usually accompanied by strong exchanges of water and heat and demonstrate a nonlinear relationship between precipitation and ecosystem productivity. The intensity (duration) of extreme precipitation is intensifying (decreasing) over most areas of the globe, whereas three-dimensional precipitation events are becoming more concentrated. Atmospheric dynamics play a key role in shaping the hook structure. The structure is not stable; it shifts under climate change and is projected to result in a 10–10% intensification in precipitation by the end of this century. Moderate levels of precipitation contribute to carbon assimilation in ecosystems, and the response of the carbon budget to precipitation is relatively stable under climate change. [ABSTRACT FROM AUTHOR]

Droughts are one of the climate extremes that occur frequently in drylands, constraining the terrestrial carbon uptake and water cycle processes. Studies about the long-term changes in the effect of drought stress on dryland ecosystems under global warming are still insufficient so far. Here we comprehensively investigate long-term changes in droughts and the effect of drought stresses on ecosystems across global drylands for 1982–2015, and further reveal changes in the configurations of the key meteorological and ecological factors of droughts, by using observation and reanalysis datasets. Climatically, the spatial patterns of intensity, occurrence, duration and severity of all drought categories across global drylands are highly consistent with each other. Associated with severe droughts, drylands witness insufficient precipitation (−12.4 mm mon−1 area-averaged over global drylands), warmer temperature (0.6°C), water deficit (−19.0 mm mon−1), higher atmospheric aridity (0.06 kPa), lower soil moisture (−0.03 m3 m−3), suppressed vegetation growth and declined carbon uptake (−0.13 g C m−2 d−1). The affected area, occurrence, duration and severity for mild to severe droughts in drylands and the anomalies of meteorological and ecological factors for all drought categories have increased significantly during 1982–2015. Specifically, when droughts occur, the precipitation deficit is weakened at a rate of 3.7–9.6 mm mon−1 (30 yr)−1, the higher temperature (atmospheric aridity) is further intensified at 0.71–0.87°C (30 yr)(39–47 Pa (30 yr)−1), the water (soil moisture) deficit is relieved at 1.7–5.1 mm mon−1 (30 yr)−1 (4.1×10−3–7.4×10−3 m3 m−3 (30 yr)−1), and the suppressed vegetation growth is generally alleviated at 0.98×10−2–1.2×10−2 (30 yr)−1. Since the 2000s, the increasing trend in the suppressed vegetation growth during droughts tends to stagnate over about 50% of the dryland area. By checking the probability density function, the configurations of the key meteorological and ecological factors of droughts show significant differences between the periods before and after 2000. The probability of drought stress caused by precipitation and soil moisture deficit has decreased by 20% and 10%, respectively, while that caused by higher temperature and atmospheric aridity has been doubled, and increased by 26% and 15%, respectively. Thus, the impact of drought stress on dryland ecosystems caused by atmospheric aridity are increasing under global warming. [ABSTRACT FROM AUTHOR]

In this study, we investigate the climate attribution of the 21·7 Henan extreme precipitation event. A conditional storyline attribution method is used, based on simulations of the event with a small-domain high-resolution cloud-resolving model. Large-scale vertical motion is determined by an interactive representation of large-scale dynamics based on the quasi-geostrophic omega equation, with dynamical forcing terms taken from observation-based reanalysis data. It is found that warming may lead to significant intensification of both regional-scale (10–14% K−1, depending on convective organization) and station-scale precipitation extremes (7–9% K−1). By comparing clustered convection organized by a localized surface temperature anomaly and squall-line convection organized by vertical wind shear, we further explored how convective organization may modify precipitation extremes and their responses to warming. It is found that shear convective organization is much more sensitive to large-scale dynamic forcing and results in much higher precipitation extremes at both regional and station scales than unorganized convection is. The clustered convection increases station-scale precipitation only slightly during heavy precipitation events. For regional-scale extreme precipitation sensitivity, shear-organized convection has a larger sensitivity by 2–3% K−1 than that of unorganized convection, over a wide temperature range, due to its stronger diabatic heating feedback. For the station-scale extreme precipitation sensitivity, no systemic dependence on convective organization is found in our simulations. [ABSTRACT FROM AUTHOR]

In the context of global warming, glaciers in the Asian High Mountains (AHMs) are shrinking at an accelerating rate. Projecting their future change is helpful for understanding the hydrological and climatic effects related to glacier retreat. Here, we projected glacier change in the AHMs from 1979 to 2100 under shared socioeconomic pathway (SSP) scenarios from the perspective of temperature, equilibrium-line altitude (ELA), and accumulation area. The annual mean temperature in the AHMs increased by 1.26°C from 1979 to 2014, corresponding to an increase of 210 m in the mean ELA and a decrease of 1.7×104 km2 in the glacier accumulation area. Under the SSP2-4.5 (SSP5-8.5) scenario, the annual mean temperature in the AHMs would increase by 2.84°C (3.38°C) in 2040–2060 relative to that in 1850–1900, leading to the mean ELA reaching an elevation of 5661 m (5777 m). The accumulation area in the AHMs decreased by 46.3% from 1995 to 2014 and was projected to decrease by 60.1% in 2040–2060. Moreover, the annual mean temperature in the AHMs was projected to increase by 3.76°C (6.44°C) in 2080–2100 relative to that in 1850–1900, corresponding to the ELA reaching an elevation of 5821 m (6245 m) and the accumulation area decreasing to 1.8×104 km2 (0.5×104 km2). These data suggest that the conditions for glacier development will disappear in most of the AHMs, except for extreme high-altitude regions in the Tianshan, Pamir, and Himalaya Mountains. Under the SSP2-4.5 (SSP5-8.5) scenario, when the global mean temperature increases 1.5°C (2°C) above pre-industrial levels, the annual mean temperature will increase by 2.12°C (2.86°C) and the accumulation area will decrease by 15% (48%) in the AHMs compared with that in 1995–2015. Therefore, a 1.5°C increase in global warming would keep 40% more of the glacial accumulation area (1.5×104 km2) in the AHMs compared to a 2°C increase in global warming. [ABSTRACT FROM AUTHOR]

Permafrost is a potential mercury (Hg) pool released by thawing, which can raise the risk of Hg pollution under global warming. Tree rings are useful archives of environment-specific Hg exposure over long periods. We determined Hg concentrations in tree rings of two dominant tree species (Larix gmelinii Rupr. and Pinus sylvestris var. mongolica) at permafrost sites in northeastern China. The biweighted mean Hg concentrations ranged from 0.36 to 3.96 ng g−1 from 1840 to 2014. The tree-ring width had no significant influence on the Hg concentration. Larch Hg increased slightly before the 1970s and peaked in the 1990s. However, the pine Hg concentration increased continuously until the 1930s, decreased rapidly until the 1970s, then rose to a peak in the late 1980s. The change of Hg concentrations in larch and pine revealed a time offset of 4 to 5 years, which implied possibly high mobility of Hg in pine tree rings. Higher Hg concentrations from 1920 to 1960 and subsequent decreases in isolated permafrost forests revealed the local geographical Hg cycling history. Lower Hg concentrations and faster increases in larch suggest the role of additional winter Hg loading for the evergreen pine and species-specific differences in root absorption in response to melting permafrost. Our results highlight possible geographical impacts on tree-ring Hg records, improve understanding of Hg cycles in permafrost forest, and suggest a need to sample additional species in a range of permafrost environments. [ABSTRACT FROM AUTHOR]

Understanding hydroclimatic patterns and their possible driving mechanisms during distinct climate periods over the last 1500 years—such as the Medieval Warm Period (MWP), the Little Ice Age (LIA), and the Current Warm Period—is crucial for predicting future changes to monsoon precipitation in southwest China under global warming scenarios. In this study, based on 210Pb and 137Cs dating of surface sediments and AMS 14C dating of terrestrial plant residues, we establish a robust age model that covers the last ∼1500 years (AD 439–2012) at Lake Yihai in southwest China. We use analyses of multiple geochemical proxy indices, including loss on ignition at 550°C, total organic carbon, total nitrogen, C/N ratios, and stable carbon isotopes of organic matter to reconstruct changes in summer monsoon precipitation at Lake Yihai during the last ∼1500 years. The results show that, over southwest China, warm and dry climate conditions prevailed during the MWP (AD 1000–1400) and the past 200 years, whereas conditions during the LIA (AD 1400–1800) were cold and wet. This is consistent with evidence from other geological records over southwest China, such as stalagmite and lake sediment data. Similar hydroclimatic patterns have occurred over the last 1500 years in adjacent tropical/subtropical monsoon regions where the climate is similarly dominated by the Indian summer monsoon (e.g., South China, the South China Sea, Southeast Asia, Northeast India). We suggest that the meridional migration of the mean position of the Inter-tropical Convergence Zone, and El Niño/Southern Oscillation conditions which are linked to tropical Pacific sea surface temperature, are responsible for centennial-scale hydroclimatic patterns over southwest China and adjacent areas during the last 1500 years. [ABSTRACT FROM AUTHOR]

In this study, the long-term trend of water vapor over the Tibetan Plateau (TP) in boreal summer is investigated by using observation and reanalysis data from 1979 to 2019. The historical experiment simulations of 19 models that participated in the Coupled Model Intercomparison Project phase 6 (CMIP6) are evaluated, and the future variation tendency under four emission scenarios is projected. The results indicate that the water vapor content and the net water vapor budget over the TP show notable increasing trends, which are mainly manifested by a significant increase in the net water vapor import and a significant decrease in the water vapor export on the eastern boundary of the TP. This is mainly due to an anomalous anticyclone from Lake Baikal to the Mongolian Plateau. The CMIP6 multi-model ensemble can well simulate the variation characteristics of the TP net water vapor budget. The projection results indicate that by the end of the twenty-first century, the water vapor content, the net water vapor import and precipitation over the TP will increase. Under a high-emissions scenario and compared with the current period (1991–2014), these three variables will increase by 47.99%, 59.77% and 18.59% in the long term (2081–2100), respectively. The significant enhancement of meridional water vapor transport over the northern TP may be the main reason for the increase in humidity over the TP. [ABSTRACT FROM AUTHOR]

Global warming and its climatic and environmental effects have mainly been investigated in terms of the absolute warming rate. Little attention has been paid to the contribution of absolute warming rate to variability on various time scales of surface air temperature (SAT), which may be a more direct index for measuring the ecoclimatic effect of warming trend. The present study analyzed the role of secular warming trend in the variations of global land SAT for 1901–2016. Less than one-third of annual SAT variations were contributed by the warming trend over large parts of the globe generally. The ratios were up to two-thirds over eastern South America, parts of South Africa and the regions around the southwestern Mediterranean and Sunda islands where the absolute warming rate was moderate but the endemic species were undergoing exceptional loss of habitat. The ratios also exhibited smallest seasonal difference over these regions. Therefore, the ratio of the warming trend to the SAT variations may be a better measure compared to the absolute warming rate for the local ecoclimate. We should also pay more attention to the regions with high ratio, not only the regions with the high absolute warming rate. [ABSTRACT FROM AUTHOR]

The unexpected global warming slowdown during 1998–2013 challenges the existing scientific understanding of global temperature change mechanisms, and thus the simulation and prediction ability of state-of-the-art climate models since most models participating in phase 5 of the Coupled Model Intercomparison Project (CMIP5) cannot simulate it. Here, we examine whether the new-generation climate models in CMIP6 can reproduce the recent global warming slowdown, and further evaluate their capacities for simulating key-scale natural variabilities which are the most likely causes of the slowdown. The results show that although the CMIP6 models present some encouraging improvements when compared with CMIP5, most of them still fail to reproduce the warming slowdown. They considerably overestimate the warming rate observed in 1998–2013, exhibiting an obvious warming acceleration rather than the observed deceleration. This is probably associated with their deficiencies in simulating the distinct temperature change signals from the human-induced long-term warming trend and or the three crucial natural variabilities at interannual, interdecadal, and multidecadal scales. In contrast, the 4 models that can successfully reproduce the slowdown show relatively high skills in simulating the long-term warming trend and the three key-scale natural variabilities. Our work may provide important insight for the simulation and prediction of near-term climate changes. [ABSTRACT FROM AUTHOR]

The history and mechanisms of dust storms in northern China remain unclear owing to the paucity of reliable long-term, high-resolution geological records. In this study, we reconstructed the dust storm history of the last ~500 years in northern China, based on sedimentary coarse fraction (>63 µm) of a well-dated core from Lake Daihai, Inner Mongolia. The high-resolution data reveal three intervals of frequent dust storms: AD 1520–1580, AD 1610–1720, and AD 1870–2000. The dust storm events in the Lake Daihai area were broadly synchronous with those inferred from other historical or geological records and generally occurred during cold intervals. Changes in the intensity of Siberian High and the westerlies modulated by temperature variations are the likely major factors controlling dust storm dynamics. An interesting feature is that although the intensities of dust storms have been systematically increased during the recent warming period, a clear decreasing trend within this period is evident. The recent increase in average dust storm intensity may be ascribed to an increase in particle supply resulting from a rapid increase in human activity, whereas the weakening trend was likely caused by decreases in average wind speed resulting from the recent global warming. [ABSTRACT FROM AUTHOR]

The impact of global warming on the climate of northern China has been investigated intensively, and the behavior of the East Asian monsoon during previous intervals of climatic warming may provide insight into future changes. In this study, we use paleovegetation records from loess and lake sediments in the marginal zone of the East Asian summer monsoon (EASM) to reconstruct the EASM during the interval of warming from the Last Glacial Maximum (LGM) to the Holocene. The results show that during the LGM, desert steppe or dry steppe dominated much of northern China; in addition, the southeastern margin of the deserts east of the Helan Mountains had a distribution similar to that of the present-day, or was located slightly further south, due to the cold and dry climate caused by a strengthened East Asian winter monsoon (EAWM) and weakened EASM. During the last deglaciation, with the strengthening of the EASM and concomitant weakening of the EAWM, northern China gradually became humid. However, this trend was interrupted by abrupt cooling during the Heinrich 1 (H1) and Younger Dryas (YD) events. The EASM intensified substantially during the Holocene, and the monsoon rain belt migrated at least 300 km northwestwards, which led to the substantial shrinking of the desert area in the central and eastern part of northern China, and to the large expansion of plants favored by warm and humid conditions. Paleoclimatic records from the marginal zone of the EASM all show that the EASM reached its peak in the mid-Holocene, and past global climatic warming significantly strengthened the EASM, thereby greatly improving the ecological environment in northern China. Thus, northern China is expected to become wetter as global warming continues. Finally, high resolution Holocene vegetation records are sparse compared with the numerous records on the orbital timescale, and there is a need for more studies of Holocene climatic variability on the centennial-to-decadal scale. [ABSTRACT FROM AUTHOR]

We report a 1556 year-long tree-ring width chronology for the Hexi Corridor, in the arid Northwestern China, established by applying the signal-free regional curve standardization method to 416 juniper ring-width series. We found that drought in early summer (May–June) is the primary controlling factor for tree growth in this area. We then developed an early summer moisture (i.e., scPDSI) reconstruction from 455 CE to present. Our reconstruction captures multi-centennial scale moisture variations, showing two long-term dry periods during 800–950 CE and 1000–1200 CE, and two long-term wet periods during 1200–1450 CE and 1510–1620 CE. We found strong similarities between hydroclimatic changes in the Hexi Corridor and Qaidam Basin from interannual to centennial timescales; however, at multi-centennial (>300 years) timescales, hydroclimatic variations in the two regions showed significant regional differences. The Hexi Corridor witnessed a generally dry Medieval Climate Anomaly (MCA, here 800–1200 CE) and the drying 20th century, whereas the Qaidam Basin experienced high-precipitation periods during the MCA and 20th century. The different correlation pattern with Northern Hemisphere temperature suggest that the Qaidam Basin will receive more precipitation under global warming, whereas the Hexi Corridor will become dryer in the future. [ABSTRACT FROM AUTHOR]

The two key mechanisms for biologically driven carbon sequestration in oceans are the biological pump (BP) and the microbial carbon pump (MCP); the latter is scarcely simulated and quantified in the China seas. In this study, we developed a coupled physical-ecosystem model with major MCP processes in the South China Sea (SCS). The model estimated a SCS-averaged MCP rate of 1.55 mg C m−2 d−1, with an MCP-to-BP ratio of 1:6.08 when considering the BP at a depth of 1000 m. Moreover, the ecosystem responses were projected in two representative global warming scenarios where the sea surface temperature increased by 2 and 4°C. The projection suggested a declined productivity associated with the increased near-surface stratification and decreased nutrient supply, which leads to a reduction in diatom biomass and consequently the suppression of the BP. However, the relative ratio of picophytoplankton increased, inducing a higher microbial activity and a nonlinear response of MCP to the increase in temperature. On average, the ratio of MCP-to-BP at a 1000-m depth increased to 1:5.95 with surface warming of 4°C, indicating the higher impact of MCP in future ocean carbon sequestration. [ABSTRACT FROM AUTHOR]

Global warming, the most severe faunal mass extinction and the shift of biogeochemical cycles were observed in the ocean across the Permian-Triassic boundary about 252 million years ago, providing an analog to understanding the modern oceans. Along with the progressive global warming, the biogeochemical cycle was documented to show a shift from the decoupled processes of carbon, nitrogen and sulfur prior to the mass extinction to the coupled biogeochemical processes during faunal mass extinction. The coupled biogeochemical cycle was further observed to shift from the coupled C-N processes during the first episode of the faunal mass extinction to the coupled C-N-S processes during the second episode, diagnostic of the progressive development of more deteriorated marine environmental conditions and the more severe biotic crisis across the Permian-Triassic boundary. The biogeochemical cycles could thus be an indication to the progressive collapse of marine ecosystems triggered by the global warming in Earth history. In modern oceans, the coupled C-N cycle triggered by the global warming was observed in some regions. If these local C-N processes develop and expand to the global oceans, the coupled C-N-S processes might be brought into existence and the marine ecosystems are inevitable to suffer from complete collapse as observed at 252 million years ago. [ABSTRACT FROM AUTHOR]

Solar geoengineering has been proposed as a potential mechanism to counteract global warming. Here we use the University of Victoria Earth System Model (UVic) to simulate the effect of idealized sunshade geoengineering on the global carbon cycle. We conduct two simulations. The first is the A2 simulation, where the model is driven by prescribed emission scenario based on the SRES A2 CO2 emission pathway. The second is the solar geoengineering simulation in which the model is driven by the A2 CO2 emission scenario combined with sunshade solar geoengineering. In the model, solar geoengineering is represented by a spatially uniform reduction in solar insolation that is implemented at year 2020 to offset CO2-induced global mean surface temperature change. Our results show that solar geoengineering increases global carbon uptake relative to A2, in particular CO2 uptake by the terrestrial biosphere. The increase in land carbon uptake is mainly associated with increased net primary production (NPP) in the tropics in the geoengineering simulation, which prevents excess warming in tropics. By year 2100, solar geoengineering decreases A2-simulated atmospheric CO2 by 110 ppm (12%) and causes a 60% (251 Pg C) increase in land carbon accumulation compared to A2. Solar geoengineering also prevents the reduction in ocean oxygen concentration caused by increased ocean temperatures and decreased ocean ventilation, but reduces global ocean NPP. Our results suggest that to fully access the climate effect of solar geoengineering, the response of the global carbon cycle should be taken into account. [ABSTRACT FROM AUTHOR]

Using high-resolution ice core and tree ring proxies for sea ice extent (SIE), we reconstructed a robust time series of autumn SIE over the Barents-Kara (B-K) sector of the Arctic from AD1289-1993. After intercomparing the results and statistical parameters using the ordinary least squares regression (OLSR), the principle component regression (PCR) and the partial least squares regression (PLSR) methods, SIE time series were synthesized into a more robust series using the weighted average method, which used the explained variances as weights. The results showed that from the end of the 13th century to the end of 18th century, the autumn B-K SIE was large, with large variations and a slightly expanding trend overall. This reflected significant multidecadal oscillations under the Little Ice Age (LIA) background. The B-K SIE began to decrease at the end of the 18th century, and a shrinking trend became significant during the second half of the 19th century, which lasted into the 1930s-1940s. The 1930s-1940s was a period with a relatively low SIE in the B-K Sea, and the SIE had a short period of expansion from the 1940s-1970s. However, the B-K SIE has continuously and significantly shrank since the 1970s. The reduction in the B-K SIE since the end of the 18th century has been unprecedented in both duration and speed over the last 700 years. The B-K SIE has retreated significantly since the 1970s, with a speed 6.18 times greater than the former mean retreating speed. The industrial revolution may be a dominant factor in this result. The Arctic SIE in recent years may be the lowest it has been over the last millennium. [ABSTRACT FROM AUTHOR]

Based on Marx-Planck coupled model simulations and in situ hydrography measurements, the volume transport of ocean currents and associated carbon fluxes across the continental margin from the continental shelf to the deep ocean in the East China Sea during winter are estimated. Because cross-shelf currents in the Yellow and East China seas are much stronger in winter than in other seasons and are subducted into the subsurface Kuroshio, the cross-shelf burial of carbon takes place mainly in winter. The analyses show prominent cross-shelf transports during winter in the Yellow and East China seas, with annual mean offshore transport across a section from Taiwan to Cheju at 3.92 Sv (1 Sv=106 m3 s−1). Net transport across the section was 0.82 Sv off the shelf, determined by the difference between Taiwan and Cheju strait transports. Net cross-shelf transports of dissolving inorganic carbon (DIC), dissolved organic carbon (DOC), and particulate organic carbon (POC) in winter were 98, 12, and 0.1 million tons, respectively. Under global greenhouse gas emission reduction (RCP4.5) and continuous increase (RCP8.5) scenarios, this cross-shelf transport has an increasing trend. The transports across the Taiwan-Cheju section in winter are predicted to increase by 0.54 and 0.65 Sv from 2006 to 2099, with rates of increase 15.3% and 19.6%, respectively. Associated with the transport increase, the cross-shelf fluxes of DIC, DOC and POC increase by as much as 15.4-25.2%. Cross-shelf carbon fluxes in the East China Sea during winter are evaluated for the first time under the global warming scenarios, showing the importance of cross-shelf transport in the carbon cycle of the China marginal seas. [ABSTRACT FROM AUTHOR]

This study quantitatively investigates the long-term dynamics of the association between natural disasters and the migration of agriculturists in historical China. Population pressure is also studied because migration is a population density-dependent phenomenon. This study has adopted correlation analysis, multivariate linear/Poisson regression analyses, and Granger causality analysis to verify the linkages of natural disaster-migration and population-migration in historical China by collecting updated datasets. This study is the first attempt to reveal that the duration effects of natural disasters on the migration of agriculturalists are short-term and almost instantaneous. Although the agrarian society has a low buffering capacity, the effects of natural disasters within a short-term scale could be relieved to some extent. However, population pressure can push migration on a long-term scale despite its limited forcefulness. [ABSTRACT FROM AUTHOR]

The tropical Pacific experienced a sustained warm sea surface condition that started in 2014 and a very strong El Niño event in 2015. One striking feature of this event was the horseshoe-like pattern of positive subsurface thermal anomalies that was sustained in the western-central equatorial Pacific throughout 2014-2015. Observational data and an intermediate ocean model are used to describe the sea surface temperature (SST) evolution during 2014-2015. Emphasis is placed on the processes involved in the 2015 El Niño event and their relationships with SST anomalies, including remote effects associated with the propagation and reflection of oceanic equatorial waves (as indicated in sea level (SL) signals) at the boundaries and local effects of the positive subsurface thermal anomalies. It is demonstrated that the positive subsurface thermal anomaly pattern that was sustained throughout 2014-2015 played an important role in maintaining warm SST anomalies in the equatorial Pacific. Further analyses of the SST budget revealed the dominant processes contributing to SST anomalies during 2014-2015. These analyses provide an improved understanding of the extent to which processes associated with the 2015 El Niño event are consistent with current El Niño and Southern Oscillation theories. [ABSTRACT FROM AUTHOR]

The Coupled Model Inter-comparison Project Phase 5 (CMIP5) contains a group of state-of-the-art climate models and represents the highest level of climate simulation thus far. However, these models significantly overestimated global mean surface temperature (GMST) during 2006-2014. Based on the ensemble empirical mode decomposition (EEMD) method, the long term change of the observed GMST time series of HadCRUT4 records during 1850-2014 was analyzed, then the simulated GMST by 33 CMIP5 climate models was assessed. The possible reason that climate models failed to project the recent global warming hiatus was revealed. Results show that during 1850-2014 the GMST on a centennial timescale rose with fluctuation, dominated by the secular trend and the multi-decadal variability (MDV). The secular trend was relatively steady beginning in the early 20th century, with an average warming rate of 0.0883°C/decade over the last 50 years. While the MDV (with a ~65-year cycle) showed 2.5 multi-decadal waves during 1850-2014, which deepened and steepened with time, the alarming warming over the last quarter of the 20th century was a result of the concurrence of the secular warming trend and the warming phase of the MDV, both of which accounted one third of the temperature increase during 1975-1998. Recently the slowdown of global warming emerged as the MDV approached its third peak, leading to a reduction in the warming rate. A comparative analysis between the GMST time series derived from HadCRUT4 records and 33 CMIP5 model outputs reveals that the GMSTs during the historical simulation period of 1850-2005 can be reproduced well by models, especially on the accelerated global warming over the last quarter of 20th century. However, the projected GMSTs and their linear trends during 2006-2014 under the RCP4.5 scenario were significantly higher than observed. This is because the CMIP5 models confused the MDV with secular trend underlying the GMST time series, which results in a fast secular trend and an improper MDV with irregular phases and small amplitudes. This implies that the role of atmospheric CO in global warming may be overestimated, while the MDV which is an interior oscillation of the climate system may be underestimated, which should be related to insufficient understanding of key climatic internal dynamic processes. Our study puts forward an important criterion for the new generation of climate models: they should be able to simulate both the secular trend and the MDV of GMST. [ABSTRACT FROM AUTHOR]

Climate warming, one of the main features of global change, has exerted indelible impacts on the environment, among which the impact on the transport and fate of pollutants has aroused widespread concern. Persistent organic pollutants (POPs) are a class of pollutants that are transported worldwide. Determining the impact of climate warming on the global cycling of POPs is important for understanding POP cycling processes and formulating relevant environmental policies. In this review, the main research findings in this field over the past ten years are summarized and the effects of climate warming on emissions, transport, storage, degradation and toxicity of POPs are reviewed. This review also summarizes the primary POP fate models and their application. Additionally, research gaps and future research directions are identified and suggested. Under the influence of climate change, global cycling of POPs mainly shows the following responses. (1) Global warming directly promotes the secondary emission of POPs; for example, temperature rise will cause POPs to be re-released from soils and oceans, and melting glaciers and permafrost can re-release POPs into freshwater ecosystems. (2) Global extreme weather events, such as droughts and floods, result in the redistribution of POPs through intense soil erosion. (3) The changes in atmospheric circulation and ocean currents have significantly influenced the global transport of POPs. (4) Climate warming has altered marine biological productivity, which has changed the POP storage capacity of the ocean. (5) Aquatic and terrestrial food-chain structures have undergone significant changes, which could lead to amplification of POP toxicity in ecosystems. (6) Overall, warming accelerates the POP volatilization process and increases the amount of POPs in the environment, although global warming facilitates their degradation at the same time. (7) Various models have predicted the future environmental behaviors of POPs. These models are used to assist governments in comprehensively considering the impact of global warming on the environmental fate of POPs and therefore controlling POPs effectively. Future studies should focus on the synergistic effects of global changes on the cycling of POPs. Additionally, the interactions among global carbon cycling, water cycling and POP cycling will be a new research direction for better understanding the adaptation of ecosystems to climate change. [ABSTRACT FROM AUTHOR]

The Pinus taiwanensis trees of a Chinese endemic species form pure forests at infertile sites in humid subtropical China, which can aid soil reservation and ecological resiliency at such sites. Herein, we used dendrochronological methods to investigate the growth patterns and their relationship with climate by analyzing 158 cores of 79 P. taiwanensis trees at 4 sites in their southernmost distribution in mainland China at Daiyun Mountain in Fujian Province. Tree growths at sites with favorable conditions generally showed an age-related growth trend, which decreased from approximately 5 mm to 0.5 mm in about a century. Trees in moderately stressed environments established high growth in their juvenile periods but were highly susceptible to environmental stresses such as a sharp growth decline in the 1990s. The temperature in February and the moisture in July are the major limiting factors for most of the tree growths, except for a few extremely stressed P. taiwanensis trees. The growth of the dwarf P. taiwanensis trees, with all ring diameters of the first 20 years less than 4 mm, is mainly limited by the dry climate in May. Under the potential future warming trend, drought stress can be particularly threatening to these dwarf P. taiwanensis trees, which are likely to be the germplasm resources for this species in this region. [ABSTRACT FROM AUTHOR]

The association of seasonal timing of stratospheric final warming events (SFWs) in spring and the occurrence of major and minor stratospheric sudden warming events (SSWs) in midwinter were investigated through statistical analysis, parallel comparison, and composite analysis, based on the NCEP-NCAR reanalysis dataset covering 1958-2012. It was found that the intensity and occurrence of winter SSW events can largely affect the timing of spring SFWs. Specifically, the SFW onset dates tend to be later (earlier) after the occurrence (absence) of winter major SSWs. However, the occurrence or absence of minor SSWs does not change the frequency of early and late SFWs. A parallel comparison of the temporal evolution of the anomalous circulation and planetary-waves between major SSW and minor SSW winters indicates that the stratospheric polar vortex (polar jet) will keep being anomalously stronger 30 days after major SSW onset. And the associated significant negative Eliassen-Palm (EP) flux anomalies can persist for as long as 45 days after major SSW events. In contrast, the circulation anomalies around the occurrence of minor SSW events can last only a few days. To further verify the possible influence of the occurrence of major SSWs on the seasonal timing of SFWs, composite analysis was performed respectively for the 21 major-SSW years, 15 minor-SSW years, and the 15 non-SSW years. Generally, planetary-wave activity in the extratropical stratosphere tends to be stronger (weaker) and the westerly polar jet is anomalously weaker (stronger) in major-SSW (non-SSW) winters. But in the following spring, the planetary-wave activity is weaker (stronger) accompanied with an anomalously stronger (weaker) stratospheric polar vortex. In spring after minor-SSW years, however, the stratospheric polar vortex and the westerly polar jet exhibit a state close to climatology with relatively gentle variations. [ABSTRACT FROM AUTHOR]

With the influence of global warming, the global climate has undergone significant inter-decadal variation since the late 1970s. Although El Niño-Southern Oscillation (ENSO) has been the strongest signal for predicting global climate inter-annual variability, its relation with the summer rainfall in China has significantly changed, and its indicative function on the summer rainfall in China has weakened. This has led to a significant decrease in the accuracy rate of early conceptual prediction models for the Three Rainfall Patterns in the summer of eastern China. On the basis of the difference analysis of atmospheric circulation system configuration in summer, as well as the interaction of ocean and atmospheric in previous winter between two phases, i.e. before and after the significant global warming (1951 to 1978 and 1979 to 2012, respectively), we concluded that (1) Under different inter-decadal backgrounds, the atmospheric circulations that impacted the Three Rainfall Patterns in the summer of eastern China showed consistency, but in the latter phase of the global warming, the Western Pacific Subtropical High (WPSH) was on the strong side, the position of which was in the south, and the blocking high in the Eurasia mid-high latitudes was active, while the polar vortex extended to the south, and meridional circulation intensified. This circulation background may have been conducive to the increase of the circulation frequency of Patterns II and III, and the decrease of the circulation frequency of Pattern I, thus leading to more Patterns II and III and fewer Pattern I in the summer rainfall of eastern China. (2) In the former phase, the corresponding previous winter SST fields of different rainfall patterns showed visible differences. The impact of ENSO on North Pacific Oscillation (NPO) was great, and the identification ability of which on Patterns I and II of summer rainfall was effective. In the latter phase, this identification ability decreased, while the impact of ENSO on the Pacific/North American (PNA) teleconnection pattern increased, and the identification ability of the PNA on Patterns II and III also increased. Based on the new inter-decadal climate background, this study reconstructs the conceptual prediction model for the Three Rainfall Patterns in summer of eastern China by using the previous winter PNA and the Eurasian (EU) teleconnection indexes. The fitting effect was satisfying, though it is necessary to be further tested. [ABSTRACT FROM AUTHOR]

Changes in the hydrological processes in alpine soil constitute one of the several key problems encountered with studying watershed hydrology and ecosystem stability against the background of global warming. A typically developing thermokarst lake was chosen as a subject for a study using model simulation based on observations of soil physical properties, infiltration processes, and soil moisture. The results showed that the selected thermokarst lake imposed certain changes on the soil infiltration processes and, with the degree of impact intensifying, the initial infiltration rate decreased. The greatest reduction was achieved in the area of moderate impact. However, the stable infiltration rate and cumulative infiltration gradually increased in the surface layer at a depth of 10 and 20 cm, both decreasing initially and then increasing, which is correlated significantly with soil textures. Moreover, the cumulative infiltration changed in line with steady infiltration rate. Based on a comparative analysis, the Horton model helps better understand the effect on the soil infiltration processes of the cold alpine meadow close to the chosen thermokarst lake. In conclusion, the formation of the thermokarst lake reduced the water holding capacity of the alpine meadow soil and caused the hydraulic conductivity to increase, resulting in the reduction of runoff capacity in the area of the thermokarst lake. [ABSTRACT FROM AUTHOR]

How would typhoon activity over the western North Pacific change for various scenarios of future global warming? Using the model projections of the Coupled Model Intercomparison Project phase 3 (CMIP 3) under the SRES A1B scenario, we generated summer (September) ice-free Arctic conditions, also referred to as Blue Arctic conditions, and then used the corresponding monthly sea surface temperature (SST) and a set of CO concentrations to drive an AGCM model to simulate the resulting changes in background conditions affecting typhoon activity over the western North Pacific. Our results show that, during typhoon season (June to October), atmospheric and ocean circulations over the western North Pacific would be significantly different from the present circulations. Changes in the vertical shear of zonal wind and outgoing longwave radiation (OLR) in the western North Pacific are favorable for westward and northward shift, respectively, of the location of typhoon genesis. Moreover, changes in the above fields over the key area may be conducive to less frequent typhoons. In addition, the tropical cyclone genesis potential index (GPI) over the western North Pacific would decrease (increase) east (west) of 150°E (140°E). [ABSTRACT FROM AUTHOR]

Based on the daily NCEP/DOE reanalysis II data, dates of the boreal spring Stratospheric Final Warming (SFW) events during 1979-2010 are defined as the time when the zonal-mean zonal wind at the central latitudes (65°-75°N) of the westerly polar jet drops below zero and never recovers until the subsequent autumn. It is found that the SFW events occur successively from the mid to the lower stratosphere and averagely from the mid to late April with a temporal lag of about 13 days from 10 to 50 hPa. Over the past 32 years, the earliest SFW occurs in mid March whereas the latest SFW happens in late May, showing a clear interannual variability of the time of SFW. Accompanying the SFW onset, the stratospheric circulation transits from a winter dynamical regime to a summertime state, and the maximum negative tendency of zonal wind and the strongest convergence of planetary-wave are observed. Composite results show that the early/late SFW events in boreal spring correspond to a quicker/ slower transition of the stratospheric circulation, with the zonal-mean zonal wind reducing about 20/5 m s at 30 hPa within 10 days around the onset date. Meanwhile, the planetary wave activities are relatively strong/weak associating with an out-of-/in-phase circumpolar circulation anomaly before and after the SFW events in the stratosphere. All these results indicate that, the earlier breakdown of the stratospheric polar vortex (SPV), as for the winter stratospheric sudden warming (SSW) events is driven mainly by wave forcing; and in contrast, the later breakdown of the SPV exhibits more characteristics of its seasonal evolution. Nevertheless, after the breakdown of SPV, the polar temperature anomalies always exhibit an out-of-phase relationship between the stratosphere and the troposphere for both the early and late SFW events, which implies an intimate stratosphere-troposphere dynamical coupling in spring. In addition, there exists a remarkable interdecadal change of the onset time of SFW in the mid 1990s. On average, the SFW onset time before the mid 1990s is 11 days earlier than that afterwards, corresponding to the increased/decreased planetary wave activities in late winter-early spring before/after the 1990s. [ABSTRACT FROM AUTHOR]

The projected temporal evolution in the interannual variability of East Asian summer rainfall in the 21st century is investigated here, by analyzing the simulated results of 18 coupled models under the 20th century climate experiment and scenario A1B. The multi-model ensemble (MME) mean projects two prominent changes in the interannual variability of East Asian summer rainfall in the 21st century under scenario A1B. The first change occurs around the 2030s, with a small change before and a large increase afterward. The intensity of the interannual variability increases up to approximately 0.53 mm/d in the 2070s, representing an increase of approximately 30% relative to the early 21st century. The second change happens around the 2070s, with a decrease afterward. By the end of the 21st century, the increase is approximately 12% relative to the early 21st century. The interannual variability of two circulation factors, the western North Pacific subtropical high (WNPSH) and the East Asian upper-tropospheric jet (EAJ), are also projected to exhibit two prominent changes around the 2030s and 2070 under scenario A1B, with consistent increases and decreases afterward, respectively. The MME result also projects two prominent changes in the interannual variability of water vapor transported to East Asia at 850 hPa, which occurs separately around the 2040s and 2070s, with a persistent increase and decrease afterward. Meanwhile, the precipitable water interannual variability over East Asia and the western North Pacific is projected to exhibit two prominent enhancements around the 2030s and 2060s and an increase from 0.1 kg/m in the early 21st century to 0.5 kg/m at the end of the 21st century, implying a continuous intensification in the interannual variability of the potential precipitation. Otherwise, the intensities of the three factors' (except EAJ) interannual variability are all projected to be stronger at the end of the 21st century than that in the early period. These studies indicate that the change of interannual variability of the East Asian summer rainfall is caused by the variability of both the dynamic and thermodynamic variables under scenario A1B. In the early and middle 21st century, both factors lead to an intensified interannual variability of rainfall, whereas the dynamic factors weaken the interannual variability, and the thermodynamic factor intensifies the interannual variability in the late period. [ABSTRACT FROM AUTHOR]