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To celebrate its 150 anniversary, Nature collected 10 extraordinary papers published on Nature in November, 2019. One of the papers is on the discovery of the Antarctic ozone hole, which was published by three British scientists, Joe C. Farman, Brian G. Gardiner, and Jonathan D. Shanklin, in 1985. They first showed observational evidence that Antarctic stratospheric ozone experienced drastic decrease in the early 1980s, by contrasting to the relative steady state in the 1970s. They also suggested that the ozone hole is due to human-made chlorofluorocarbons (CFCs). Nature invited Susan Solomon, who made outstanding contributions to our understanding of the ozone hole, to comment on the paper. She pointed out that “The unexpected discovery of a hole in the atmospheric ozone layer over the Antarctic revolutionized science—and helped to establish one of the most successful global environmental policies of the twentieth century.” The observational evidence by Farman et al. greatly confirmed earlier theoretical works by P. Cruzen, M. Molina, and F. Rowland who first emphasized in the 1970s that anthropogenic emissions of nitrogen oxides and CFCs would damage the ozone layer. Their observational confirmation led to the winning of the Nobel Prize in Chemistry by Cruzen, Molina, and Rowland in 1995. The discovery of the ozone hole also led to great international actions in reducing CFCs emissions and protecting the ozone layer, which is crucially important for screening solar ultraviolet radiation for surface life. A series of conventions has been organized by the United Nations, and the most successful one is the 1987 Montreal Protocol on Substances that Deplete the Ozone Layer. The Montreal Protocol and the succeeding amendments, adjustments, and decisions were subsequently negotiated to control the consumption and production of anthropogenic emissions of ozone-depleting substances (ODSs) and some hydrofluorocarbons (HFCs). Since then, ODSs emissions have been largely reduced and showed rapid decrease since the early 1990s. The global ozone layer and the ozone hole over Antarctic all have showed gradual increasing since the late 1990s. According to predictions of climate-chemistry models, the global total column ozone will return to its 1980 values by 2045 when ODSs decline to very low levels, and the Antarctic ozone hole will recover by 2060. The gradual recovery of the ozone hole, due to reducing anthropogenic emissions, from severe depletion also due to human emissions, is considered a successful story that human can protect their environment through self-efforts. It provides us with the confidence that we are able to reduce greenhouse gas emissions and to solve the problem of global greenhouse warming. In the present paper, we will first introduce the discovery of the Antarctic ozone hole by Farman et al. Then, we introduce the chemical mechanisms of the Chapman and the catalytic reactions that result in the formation of the ozone layer, and how anthropogenic perturbations caused the Antarctic ozone hole. We shall also introduce the actions that was taken by international communities to protect the ozone layer. In the final section, we point out the important implications of the discovery of the ozone hole.

The Tibetan Plateau (TP) is an important ecological security barrier for China and, indeed, for all Asia. Land use and land cover changes in the plateau not only affect the ecological environment and regional development of the plateau itself but also affect the stability and economic development of ecosystems in eastern China and other parts of Asia. This paper is based on an examination of the achievements of land use and cover change in the TP and a reanalysis of data including that of Climate Change Initiative Land Cover from 1992 to 2015; land use data provided by the Resource and Environmental Science Data Center of the Chinese Academy of Sciences for 1995, 2000, 2010 and 2015; and statistical data from Qinghai and Tibet. The paper analyzes the overall characteristics of land use and land cover changes in the TP and the spatial and temporal processes and their driving forces of land use and land cover change in typical regions and land types. This research is important not only for land change science and global change research but also for the promotion of the plateau and its adjacent areas. In recent decades, research has shown that the land use and land cover structure of the TP is stable, and the proportion of first-level land use type change was less than 7% from 1992 to 2015. Most of these changes are single time changes, with multiple land change occurring only in 1.85% of the total change area. The quality of land cover has been improved in areas where no land type change occurred. The Normalized Difference Vegetation Index (NDVI) showed an increasing trend in 24.45% of the area and a decreasing trend in only 1.31% of the area. The area of cultivated land, forest, grassland, wetland, and construction land on the plateau has increased, whereas bare land, glacier, and snow cover area has decreased. In most parts of the TP, the quality of alpine grassland has improved; however, in some areas, it has degraded at a local scale. Most of the woodland has recovered well after phased changes. Prior to 1980, there was a rapid increase in cultivated land area, but this has since become stable with only minor increases. However, the utilization intensity of cultivated land has increased significantly in recent years. Construction land has expanded significantly, and the recent growth rate has accelerated since 2010. Both the increasing speed of change and the construction land area in Qinghai Province are higher than in Tibet. There has been a general trend of a slight decrease in bare land change. In densely populated areas in the Yellow River-Huangshui River Valley and the One-River-Two-Tributaries area, land types that are closely related to human utilization such as construction land, cultivated land, and artificial woodland have undergone obvious changes. In pastoral areas, such as the Northern Tibetan Plateau and the Source Regions of The Three Rivers, overgrazing and ecological construction have significantly affected land cover. In the Qomolangma National Nature Preserve, land use types are diverse; changes are complex; and land cover is more sensitive to both climate change and human activity. There are limitations to the study of land change in the plateau, such as the difficulty of meeting the needs of ecological construction with existing data and the lack of in-depth understanding of the process of land use change and its environmental effects. Field monitoring and remote sensing techniques must be strengthened in order to clarify the process of land use intensity change and its impact on the ecological environment of the TP. These improvements will better serve the construction of an ecological security barrier and the sustainable development of the region.

Typhoon is one of the most destructive natural disasters on the earth. A lot of fruitful research has been conducted, especially from the perspective of atmospheric sciences. During a typhoon, the ocean also undergoes dramatic variabilities, which can have significant feedbacks to the atmosphere and typhoon. Generally, the sea surface temperatures (SST) decrease and inertial oscillations are greatly enhanced. The fingerprints of typhoon on the ocean are not constrained to the local sea surface, but can be extended to the ocean interior and remote areas, which play an important role in the climate change on a much longer and larger spatiotemporal scales. In addition, the mesoscale eddy accounts for a large amount of kinetic energy in the ocean. Much progress has been achieved on the responses and feedbacks of ocean eddy to typhoon, but it remains a large uncertainty for the ocean-typhoon interaction. Particularly, the three-dimensional structure of ocean eddy during typhoon is unclear due to the lack of observations. Overall, so far, there have been no comprehensive understandings of the ocean-typhoon interactions, which are believed to be a bottleneck for improving the typhoon prediction. Therefore, the mechanisms of ocean-typhoon interactions at various spatiotemporal scales, as well as their contributions to the short-term and long-term typhoon forecast, have become a hot and challenging topic for both the oceanic and the atmospheric sciences. In this paper, recent progress in the ocean-typhoon interactions is reviewed, based on several collaborative projects in China. The foci are on the local responses and feedbacks between mesoscale variabilities in the upper ocean and typhoon, the ocean-typhoon interactions at low frequency and the impacts on global climate, data assimilation during typhoon, and typhoon forecast in the ocean-atmosphere coupled framework. The major challenge to the ocean-typhoon interactions resides in the lack of persistent and reliable observations, especially the synchronized observations in both the ocean and the atmosphere. Some valuable experiments have been conducted recently and are summarized in this study. For example, mooring/buoy arrays are carefully designed and deployed in the northern South China Sea consecutively from 2014 up to now. The monitoring for a long period accumulates very useful in-situ data for the study on the ocean-typhoon interactions. In addition, several novel technics are also proposed and tested recently, such as the one using rocket-deployed dropsondes to obtain vertical profiles in the atmosphere within a typhoon, and the Iridium Argo the sampling frequency of which can be remotely and manually increased when a typhoon is coming. On the mechanisms of ocean-typhoon interaction, a hypothesis of cold suction in the ocean is proposed and examined, which is another avenue for the typhoons impacts on the subsurface in the ocean, except for the traditional concept of heat pump. Evidence for cold suction is found in in-situ observations. The new concept makes the theory for ocean-typhoon interactions more comprehensive. For the practical application, the improvement of typhoon prediction is the golden goal. A lot of efforts have been put into the data assimilation, which synthesizes data from different resources, such as the remote sensing data of the sea surface properties and the Argo data for the ocean interior. Improved data assimilation methods are proposed to facilitate the extreme conditions during typhoon. Until now, most operational typhoon forecast still rely on the atmosphere-only model. Nevertheless, the atmosphere-ocean-wave coupled systems have been established and evaluated. Some improvement has been shown for the operational typhoon forecast. Finally, some key scientific problems and technical challenges are raised in this paper, which are expected to shed light on the future studies on the ocean-typhoon interaction.

Palynology is a branch of botany with an increasingly important role in the development of modern nature science. It was originally established in Europe during the early twentieth century and has flourished in China since the 1950s. This paper discusses the development of palynology in China from the historical, contemporaneous, and future perspectives. Specifically, we focus on the development of Quaternary palynology since 1979. Quaternary palynology involves six research fields: plants and environment, Loess Plateau, ocean, the uplift of the Tibetan Plateau, global climate change, and environmental archaeology in this paper. Palynologists who study environmental changes mainly focus on the relationships among pollen, vegetation, and environment. The high-resolution analyses of pollen records in the surface soil and sediment profiles of Loess Plateaus have promoted the development of information about paleovegetation and paleoenvironment and enabled the comparison of past climate changes and effects of human activities with global changes. By analyzing pollen data from surface water samples and marine drilling cores, palynologists have made significant progress in elucidating the high-resolution evolutionary history of paleovegetation, paleoclimate, and paleomonsoon in South China Sea and its surrounding regions on the time scales of several million years. Such progress has benefitted research on global sea level changes. The uplift of the Tibetan Plateau has been a hot area of research for several years. Palynologists have explored the vegetational, climatic, and environmental features of different periods, such as the Late Glacial, the Last Glacial Maximum, the Younger Dryas, and the Holocene Megathermal, to reveal the mechanism and process of the uplift of the Tibetan Plateau. The application of Quaternary palynology to environmental archeology not only facilitates understanding of the needs of the economic life and food structure of ancestral humans, the evolution of paleoenvironment and the rise and fall of culture, but also promotes current research on the origin of human, agricultural and civilization. Although Quaternary palynology has made remarkable achievements in many research fields, three problems require urgent solutions. First, the low magnification and resolution of optical microscopy complicate palynological identification on the species level and introduce a degree of uncertainty to the reconstruction of paleovegetation, paleoenvironment and paleoclimate. Second, pollen does not show a simple linear relationship with vegetation. Thus, a reliable pollen-vegetation relationship model remains to be established. Third, research on modern pollen processes, which includes pollen production, transportation, source, deposition, and preservation, has a crucial role in the correct explanation of pollen data and quantitative reconstruction of the paleovegetation and paleoenvironment. Global changes and the impact of environmental evolution have provided excellent opportunities and new challenges for the development of Quaternary palynology in the new century. These opportunities and challenges are as follows: First, the accuracy of pollen identification must be improved to establish a reliable pollen-vegetation relationship model. Second, systemic theoretical studies on modern pollen processes, such as pollen production, transportation, source, deposition, and preservation, should be conducted using surfaces, atmosphere, water, and rock as media. Third, the reconstruction of paleovegetation and paleoclimate from the qualitative and quantitative analyses of high-resolution pollen assemblages should receive additional efforts. Pollen records should be analyzed using various mathematical methods. Finally, to distinguish the role of climate change and human activities in vegetation and climate dynamics, human land use data, surface and fossil pollen data, and meteorological data can be combined to quantify paleovegetation and land use patterns using appropriate mathematical models. Therefore, only by relying on the integration of multidisciplinary data and academic cooperation with colleagues at home and abroad can we further improve the Quaternary palynological research in China and better serve the needs of our society and national strategies.

At the beginning of 21st century, a study suggested that Northwest China’s climate is becoming warmer and more humid. However, there were doubts about this conclusion because the humidification changes on a small scale only last for a short period, and also suspicions about the development, duration, and impact of the warming-wetting trend in this region. This paper sets out several factors, such as the area, intensity of humidification, and comprehensiveness of the wetness index, to characterize the wetting degree. Furthermore, by using measured climate data, CRU data, climate scenario predictions, and ecological and hydrological data, we systematically analyze temporal and spatial evolution of the warming-wetting trend in Northwest China. Studies have shown that Northwest China has experienced two warming periods during the last century, i.e., the 1940s, and the period from the 1960s to the present (the current warming period). The latter is more substantial. The precipitation in the west and east part of Northwest China has a seesaw change process in many periods. However, humidification has simultaneously occurred in both regions since the beginning of this century. The current precipitation in the west part of Northwest China has far exceeded any period over the past 100 a. In contrast, the east part’s recent rainfall is still currently lower than that of the 1950s and 1960s. Since 1961, Northwest China’s west region has experienced consistent humidification, which has been more pronounced since 1987. Simultaneously, the east part was drying from 1961 to 1997, and has become humid since 1997. The temperature, precipitation, and aridity index changes in the west part show the same patterns. In most periods, the west part was either cold-dry or warm-wet. In comparison, such consistency of the temperature, precipitation, and aridity changes does not exist in the east region. Before this century, warm-wet climates rarely occurred in the east region, having become more frequent. This is probably due to the different dominant temperatures and precipitation processes in the west and east regions. From a spatial point of view, the temperature increases in the whole of Northwest China, and the precipitation increases in the west region and decreases in the east region. The area with increasing rainfall has become larger during the past three climatic periods, and currently covers the whole of Northwest China. The precipitation, aridity index, and comprehensive humidity index in Northwest China have a non-linear increasing trend. The expanding humidity trend has been significant since the beginning of this century. The current warming and humidification have not changed the basic climate pattern in Northwest China. However, if the current trend continues, they would change the climate pattern in the future. Such climate change may result from the simultaneous enhancement of the westerly circulation and the East Asian summer monsoon circulations in this century. The climate warming and humidification in Northwest China significantly impacted extreme weather events, water resources, ecological environment, and agriculture during this century. This research will provide a basis for decision-making on issues such as implementing the Western development strategy in the new era, the ecological protection and high-quality development of the Yellow River Basin, environmental construction planning, and water resources management policies in Northwest China.

Climate change, sea-level rise, land subsidence, and rapid urbanization are likely to increase flood risk in low-lying coastal cities in the future, posing serious challenges to urban sustainability. To quantitatively assess the future trends of flood risks and to carry out effective adaptation measures are among the hot topics for flood risk management. A sound answer needs fine-scale data to support an integrative analysis of hydrology-hydrodynamic processes, socio-economic impacts, and adaptation measures. In this regard, this paper puts forward a set of multidisciplinary and comprehensive methods to address the frontier scientific issues. First, internet big data and machine learning methods were adopted to map the building footprint, height, and its economic values, providing a fine-scale spatial and economic information of elements at risk. The residential building footprint was mapped with an accuracy of 92.8%, and the housing price was derived via web crawler from different online real estate websites. Second, the hydrology-hydrodynamic models of TOMAWAC, TELEMAC and MIKE 1D/2D were integrated to simulate four storm-surge flooding scenarios. The scenarios are based on the real Typhoon event TC9711 on August 18, 1997, whereby the wind, wave, tide, 1D flood, and 2D flood processes are simulated and flood scenarios of four different return periods are extrapolated. Especially, for future scenarios in 2050, sea level rise and land subsidence are also considered. Third, the expected annual damage (EAD) is estimated via risk analysis technique with combination of flood maps in the four return periods and the fine-scale exposure data. Finally, a cost-benefit analysis was done to evaluate the cost-effectiveness of two flood adaptation measures, i.e., dry flood-proofing and wet flood-proofing measures, for residential buildings. Taking Shanghai as an example, the above methods were applied to comprehensively assess the storm-caused flood risk of residential buildings, its future trends to 2050, and the costs and benefits of two adaptation measures. The results show that: (1) Sea-level rise and land subsidence will significantly exacerbate the flood risks in Shanghai. (2) Under the three Representative Concentration Pathways (RCP4.5, RCP8.5 and RCP8.5 High-end), the area of exposed residential buildings in Shanghai by 2050 may reach 31−49 km2 (4%–6% of total building area) for a 1/200-year storm flood event and 180–206 km2 (14%–16%) for a 1/5000-year event. (3) The EAD of residential buildings in 2017 is 440 million CNY (65.4 million USD), which can increase 1.6–2.0 times and reach to CNY 700 million–900 million (104.0 million–133.8 million USD) in 2050. (4) The implementation of both dry and wet flood-proofing measures could potentially reduce the EAD by 76%–79% and 88%–90%, respectively. Both measures are considerably cost-effective: the net present values of dry and wet flood-proofing measures are 2.84 billion–5.53 billion CNY (0.4 billion–0.8 billion USD) and 5.85 billion–9.94 billion CNY (0.9 billion–1.5 billion USD), and the benefit/cost ratios are 1.9–2.4 and 7.9–9.8 respectively. This indicates that the cost-effectiveness of dry flood-proofing measures is less than that of wet measure. Our findings can provide both scientific understanding and effective adaptation measures for mitigating the future flood risk in Shanghai. These multidisciplinary methods could also be applied to assess flood risk and adaptation strategies in other coastal cities.

Ecological meteorology is an emerging earth science subject in response to the current environmental crisis and has become a secondary subject of atmospheric sciences. It encompasses meteorological science and technological support for national ecological civilization construction, especially national environmental protection and sustainable development. Accelerating ecological meteorology monitoring and research and establishing an operational brand is critical. The origin, concept, and primary research areas of ecological meteorology are hereby reviewed. Ecological meteorology studies the relationship between ecosystem and meteorological conditions (the core of multiple earth system sphere interactions) and serves the harmonious development of humans and nature. It includes six main aspects: (1) The patterns and laws of meteorologically induced ecosystem types and their geographical distribution; (2) the measurement of ecosystem temporal and spatial changes due to variable meteorological conditions; (3) the meteorological contribution and attribution analyses to ecological changes; (4) the feedback of ecosystem changes to the earth system; (5) the numerical modeling of ecological meteorology; (6) the interaction between meteorological conditions and ecosystems, and the principles that promote the harmonious development of humans and Nature. Compared with ecology and meteorology, ecological meteorology research has the following characteristics: (1) The time scale ranges from seconds to millennia; (2) the spatial scale ranges from the stomatal scale to the global scale; (3) the driving forces include weather, climate, atmospheric composition, climate change, and ecological and environmental changes; (4) the content emphasizes multiple earth system sphere interactions and disaster risk management; (5) the methods and technologies focus on satellite-ground integration monitoring systems and data-model fusion analyses; (6) the goal is to understand the relationship between humans and nature based on the sustainable development of the earth system. Ecological meteorology observations come from typical ecosystem research stations and regional-scale field investigations, and the operational services include assessing the ecological carrying capacity of climate resources and monitoring, evaluating, and warning for ecological meteorology disasters. This paper explains the relationship between ecological meteorology and ecological civilization construction, disaster prevention and mitigation, and how to address climate change. The primary and urgent ecological meteorology research tasks are extracting relevant information for analysis using big data and artificial intelligence, investigating ecosystem adaptations to climate change and their change attributions, exploring an ecosystem’s main meteorological disaster processes and critical meteorological conditions, analyzing the eco-physiological mechanisms of key terrestrial ecosystem phenological periods and developing simulation models of them based on multiple environmental factors, developing an eco-meteorological numerical model coupling the biological, physical, and chemical, management processes, and understanding how terrestrial ecosystem changes and sustainable development countermeasures affect the climate system. Ecological meteorology is a new and promising field that is expected to provide valuable information for the future.

Climate change in the 21st century over China and its different sub-regions is investigated in the study, based on the ensemble of a set of dynamical downscaling experiments over East Asia. The model employed in the experiments is the International Center for Theoretical Physics’ Regional Climate Model, version 4 (RegCM4), at 25-km grid spacing, driven by five different CMIP5 (phase 5 of the Coupled Model Intercomparison Project) global models under the Representative Concentration Pathways RCP4.5 and RCP8.5. The model version used was customized for better performance over the region. Ten sub-regions of China were defined, with consideration paid to local economic and societal developments, vulnerability of ecosystems, and sensitivity to future climate changes. A substantial warming in the future in China is projected, and this warming is more pronounced over the Tibetan Plateau during DJF (December-January-February) and Northwest China (where dry climate prevails) during JJA (June-July-August). A broad increase in temperature extreme indices—Namely, TXx (annual maximum daily maximum surface air temperature) and TNn (annual minimum daily minimum surface air temperature)—is reported, along with increased mean temperature. The results suggest more frequent and intense heat waves in the warm seasons, and thus more risks in terms of human health and mortality, over the sub-regions of Beijing-Tianjin-Hebei, the Yangtze Delta, the Guangdong-Hong Kong-Macao Greater Bay Area, and the Cross-Taiwan Strait Coasts, with their dense cities and populations. Meanwhile, the warming over the Tibetan Plateau may lead to degradation of frozen soil and glacial melt, and thus a greater frequency of related geological hazards, while increased evapotranspiration following the warming over the Arid and Semi-arid Northwest and Losses Plateau sub-regions may worsen the situation with respect to water resource shortages. Precipitation change in DJF shows a prevailing increase in northern China, with good agreement among the ensemble members. The increase is largest in the Northwest China sub-region. In southern China, small changes with a slight decrease in the southern part of the Yunnan-Guizhou Plateau are found. In JJA, precipitation increases over western China, the northern part of Northeast China, and the Yellow-Huai River basins, and shows small changes over other areas. A general increase in the precipitation extreme index (RX1day, the annual maximum 1-day precipitation) is found over the whole country, indicating more extreme precipitation events in the future. For the CDD index (the largest number of consecutive days when the daily precipitation amount is less than 1 mm), a general increase in the north and a decrease in the south are found. Regarding the increases of heavy precipitation events, the Arid and Semi-arid Northwest and Losses and Tibetan Plateau sub-regions, with their fragile ecosystems, may experience relatively more landslide and debris flow events; while over the more populated sub-regions, special concern is needed with respect to the likely greater frequency and more intense nature of flooding and urban-flooding events. Quantitatively, the increases in annual mean temperature, TXx, and TNn in the mid-21st (2041–2060) century relative to the present day (1986–2005) over the whole of China under RCP4.5/RCP8.5 are 1.6/2.2°C, 1.7/2.2°C, and 1.9/2.7°C, respectively. For precipitation, RX1day, and CDD, the values of change are 4%/5%, 9%/12%, and both around −2 d, respectively. The changes become more pronounced with time. By the end of the 21st century (2081–2098), under the higher scenario of RCP8.5, the changes in annual mean temperature, TXx, TNn, precipitation, RX1day and CDD are 4.6, 4.7, 5.5°C, 12%, 25%, and −4 d, respectively. Finally, the deficiencies and uncertainties that remain in projecting the future climate over the region are also outlined and discussed in the paper.

Fitting of the historic climate change with multiple linear regression (MLR) models often encounters the problem of residual autocorrelation and multiple correlation among the dependent factors, which leads the model not to be the Best Linear Unbiased Estimator (BLUE). To solve these problems, a set of sophisticated statistical modeling procedures are developed in this paper to detect the contributions of the external forcing to the global and regional land precipitation changes during the recent century. The radiative forcing (effective radiative forcing) data of multiple natural and anthropogenic factors are taken as independent variables and a combined model of MLR and Autoregressive Integrated Moving Average (ARIMA) is first used to separate the impacts of natural forcing and human activities (signals) and internal variability (noise) due to land precipitation changes since the start of the 20th century. Based on the results, a partial least squares regression (PLSR) model is further adopted to quantify the respective contributions of the each components of anthropogenic forcing. Some preliminary conclusions were drawn: (1) The combined model of MLR and ARIMA has clearly separated the influence of anthropogenic forcing signals in the global and regional (middle and high latitude in Northern Hemisphere) land precipitation anomaly at 5% significance level, and the explained variance is relatively large. (2) The PLSR model overcomes the morbidity of ordinary linear regression equations to a certain extent, and better separated the respective impact (contribution) of various natural and anthropogenic forcing factors on global and regional (middle and high latitude in Northern Hemisphere) land precipitation anomaly; and the relative strength of each factor’s contribution are determined. It has good application value for modeling and impact studies with multiple correlations among different independent variables. (3) The above combined model explains about 40% of the total variance of land precipitation anomalies change over global and middle latitude regions in Northern Hemisphere, and nearly 60% of the total variance in high latitude regions. Based on the fitting results, both the human activities and natural forcing are the deterministic impact factors of global land precipitation variations. But the natural forcing’s contribution is not significant, while human activities still explain a large part of the variance and thus have high significance for the regional land precipitation variations. In addition, the autocorrelation should also be considered as one of the important impact factors for global and regional land precipitation anomaly changes. (4) The anthropogenic aerosol and contrails have clear and significant positive contributions to the global and regional land precipitation anomalies, while the contributions of the remaining factors show obvious positive and negative differentiation, indicating that there is certain degree of uncertainty. Therefore, it is necessary to further optimize and improve the factors and models based on more accurate factor datasets for each region. (5) The modeling approach described above is primarily based on the idea to decompose and model the historical climate series. On one hand, it may put forward certain requirements for the “integrity” of the observational data; while on the other hand, it is not restricted by the study domains, climate variables and the independent variables. Moreover, it may even model/separate the anthropogenic/natural effects of climate changes in local scales. In addition, it can independently detect and analyze the relative contribution and significance of human activities or natural forcing to climate change in the historical observational series without using the climate system model. Therefore, it is proved to be a convenient approach for detecting the causes of climate change and a powerful supplement to model attribution.

The Qinghai-Tibet Plateau (QTP), also often called the Third Pole, is considered the Water Tower of Asia because it is the source of many major Asian rivers. The environmental change on the QTP can affect the climate system over the surrounding area, and the changes in glacier and river streamflow on the QTP will lead to cascading impacts in downstream area where billions of people live. This paper reviews the hydrological observations and streamflow changes of the major Asian rivers originating from the QTP. From the 1950s to the beginning of the 21st century, streamflow on the QTP overall shows large interannual variations but no significant trends. The monthly mean streamflows during the flooding seasons are the largest in the 1960s for the outlet stations on the QTP. Annual streamflow in the source region of the Yellow River decreased while that in the source region of the Yangtze River increased slightly. No significant trends of annual streamflow have been reported for the other river source regions. The mean streamflows during peak season are relatively large in the 2000s at the river source region (upper reaches) of most rivers on the QTP. An increasing trend of streamflow in spring has been found in the upper reaches of the Yellow River, the Lancang River, the Tuotuo River (of the Yangtze River), and the Lhasa River (of the Yarlung Zangbo River). The largest month of streamflow often appears in July for most stations, but in August at the Lhasa and Nuxia stations which are located in the Yarlung Zangbo River. Streamflow changes on the QTP could be mainly attributed to changes in snow and ice, as little influence from direct human activities were found. However, the examination of the streamflow changes largely relies on the hydrological observations. So far, due to data unavailability, we are still unclear about the long-term change in the streamflow on the QTP, especially the changes in recent years. The changes in ice and snow pack on the QTP could have significant impact on the downstream water resources and ecosystem. As more water resources have been generated from ice/snow melting, from a long-term perspective, water resources would be reduced along with shrinking and disappearing glaciers. Hydrological projections under future climate change suggest that streamflow in most river source regions would increase along with precipitation and increases in ice/snow melting, and hydrological extremes such as flooding would occur more frequently. Large uncertainties across Generic Circulation Models (GCMs) and hydrological models have been found in future projections of streamflow on the QTP. Reduction of ice/snow melting would aggravate the water stress conditions for both the ecosystem and human society on the QTP and its downstream areas. Sparse hydrometeorological observations in the past, particularly in the remote region of the QTP, are a major limiting factor to studies on streamflow change and its impacts. Further efforts are urgently needed to combine the advanced observation and modeling technologies to improve the observation and simulation capabilities of the water cycle over the QTP, and to provide scientific and technological support for coping with the accelerated ice/snow melting, increasing hydrological extremes and their impacts over the QTP.

Under the influence of recent global warming, the Arctic climate is continuing to experience unprecedented changes. Surface temperatures in the Arctic are increasing at a rate double that of the global average, known as the Arctic amplification. The Arctic amplification has led to a series of consequences locally such as the accelerated sea ice retreat, the continuous permafrost melting and methane release, and the marine and terrestrial ecological dynamics. It also might cause an increased frequency of extreme weather event in mid-latitudes via perturbing the strength of the polar vortex. The Arctic warming is mainly resulted from the imbalance of energy budget at both surface and top of atmosphere. In order to explore the driving mechanism of Arctic amplification, lots of efforts have been made based on model simulations and observations. Several major competing theories and related evidences have been proposed to explain their contributions to the imbalance of energy budget over the Arctic. The sea-ice albedo feedback, caused by the continuously shrinking summer sea ice potentially increasing the absorption of shortwave radiation, is believed to play a critical role in recent Arctic amplification. But certain model simulations have indicated that sea-ice albedo feedback was likely not the dominant factor—robust warming amplification still occurs in the Arctic in the absence of albedo feedback. The positive lapse rate feedback, is also thought to cause greater warming at the Arctic surface through damping the deep convection process at the bottom atmosphere because of the strong temperature inversion in the cold Arctic. However, whether the lapse rate feedback plays a dominant role in the Arctic amplification has not been widely accepted. The Planck feedback—cold region requires larger temperature increase than warm area to balance certain external radiative forcing, is also believed to contribute to the Arctic amplification. But the magnitude of its contribution remains to be further quantified. An enhanced Atlantic meridional overturning circulation (AMOC) transporting extraordinary amounts of heat northward to the Arctic Ocean has been hypothesized to substantially amplify Arctic warming and accelerate summer sea-ice melting in this region. However, evidence has instead shown significant slowing of the AMOC over the last few decades. The enhanced greenhouse effect, resulted from the increased water vapor and cloudiness, has been suggested as an important driver of the Arctic winter warming and summer sea-ice dynamics. However, whether the increased water vapor comes from the strengthened sea surface evaporation or from an enhanced atmospheric northward transportation, is still unclear. This paper elucidates the theoretical basis of all potential mechanisms, and systematically reviews the research progress of these theories. Based on the comprehensive analysis of these studies, we point out that due to the limitation of current study approaches, the data quality problems such as scarce in situ measurements, difficulty in discriminating clouds from snow cover for some remote sensing products, problematic parameterization schemes and model inputs in some reanalsysis and GCM projects, and the lack of systematic analysis for investigating the internal relations between different climate variables, the conclusions from different studies are discrepant, or even contradictory. The causes of the unprecedented climate change in the Arctic remain unclear and are still under heated debate. Therefore, the development of high quality, long-term radiative product, the optimization of the researching approaches and more accurate quantification of these feedback mechanisms, and the systematic analysis of the potential linkage between different climate variables, will help to advance the study of the Arctic amplification and climate change.

The Belt and Road Initiative was first proposed by Chinese President Xi Jinping during his visit to Kazakhstan in 2013 in order to strengthen economic ties, deepen mutual cooperation, and widen the field of development. The Silk Road Economic Belt has cultural connotations of the ancient Silk Road, a regional cooperation strategy between the Asian and African continents. This belt is important for the promotion of the Chinese economy and the development of economic and trade cooperation between China and countries located along the route. However, the Silk Road Economic Belt passes through the harshest geographical and climatic conditions in the world. The region contains complex geological structures, and is characterized by frequent earthquake activity, large differences in terrain elevation, poor engineering geological conditions, as well as intensive rainfall caused by a monsoon climate. As a result, different kinds of natural disasters, such as earthquakes, geo-hazards, floods, droughts, and dammed lakes, seriously hinder in-depth cooperation and communication between countries located along the Silk Road Economic Belt. This paper presents research on the Silk Road Economic Belt. Primary and secondary natural hazards related to geological events and climate change, such as earthquakes, climatic hazards, and geo-hazards triggered by earthquakes and extreme climatic changes, are analyzed. According to the inventory map of earthquakes, droughts, and geo-hazards, the earthquake-prone areas in this region include Central and Western Asia, the Sino-Pakistan Economic Corridor, the Sino-Mongol-Russia Junction Belt, and the New Euro-Asian Continental Bridge. The flood-prone region is located mainly in Southeastern Asia, in countries such as India, Bangladesh, and Myanmar, while the drought-prone region is located primarily in Inner Asia. The region most susceptible to geo-hazards is the mountainous area around the Tibet Plateau. The tendency of frequent natural hazards to develop and their effects on major projects along the Silk Road Economic Belt are discussed in detail. The results show that seismic activity is likely to be high until approximately 2050 and will become relatively quiescent in the second half of the 21st century. Precipitation will increase by 2%–3% until 2020, and by 5%–7% until 2050. Three high-frequency snow hazard regions are formed, including the central area of Inner Mongolia, the northern region of the Xinjiang Tianshan Range, and the Northeastern Tibet Plateau. Although the inter-annual variability of snow hazards changes significantly, the general trend shows an increase. Drought hazards have become more severe in the Qinghai-Tibet Plateau and have expanded in recent years due to global climate change and other factors. Secondary natural hazards have increased due to the rise in earthquake activity and extreme climatic changes. Strategies for disaster mitigation and natural hazards risk analysis are proposed for major projects such as high-speed railways, oil and gas pipelines, and water and electricity infrastructure. In order to reduce the risk of natural hazards and major construction, six countermeasures are proposed: (1) to perform detailed field investigations and build a database of hazards and related data, including climatic, hydrological, topographical, and geological settings; (2) to integrate engineering protection techniques against natural hazards and develop new mitigation techniques; (3) to develop a space-, sky-, and earth-based real-time monitoring and early warning system; and (4) to comprehensively assess the risk of natural hazards and major project construction. In addition, we face five key scientific and administration challenges regarding the safety of major project construction along the Silk Road Economic Belt: (1) formation mechanisms of large-scale natural hazards; (2) trend and forecast of natural hazards along the Silk Road Economic Belt in the context of climatic change; (3) dynamic and quantitative risk assessment of mega-hazards triggered by the coupling of endogenic and exogenic forces; (4) key techniques and an integrated system for risk reduction for major projects; and (5) coordination mechanism for information sharing and mitigation against mega-hazards among multiple countries.

The issue of the global climate change as well as the climate change in China is of increasingly great concern for various governments, scientific and technological communities and public. Among them, the climate change evidence, mechanism and attribution, climate change impact, as well as climate change prediction and projection have been studied intensively in China. The present paper will concisely review and assess contributions and achievement made by Chinese scientists from the international perspective, which include the following six aspects: (1) the characters tics of regional surface air temperature and tropospheric temperature in China have shown significant increasing trends. The warming rate of the surface temperature is about 1.2℃ per hundred year with its uncertainty ranging of 0.9–1.52℃. (2) The researches of water cycle have indicated that regional precipitation change has had no obvious trend at a hundred-year scale. However, the precipitation pattern has changed since 1970s with more precipitation in western China, whereas in eastern China the pattern of “drought in North and flood in South” has been observed. The annual surface humidity has taken on increasing trend. Both the small pan evaporation and potential evaporation have appeared decreasing trends. The annual runoff of most rivers in eastern China has shown decreasing trends, while that in western China has shown increasing trends. (3) It is indicated that the anthropogenic forcing has produced significant effect on the long-term variation of the East Asian monsoon. The intensity of the East Asian summer monsoon will become stronger and the monsoonal rain belt will migrate northward. (4) The sea level has been affected by the global warming. Since 1980, the rising rate of sea level in China is about 2.9 mm/a, being higher than that of the global mean. (5) The attribution of the climate change has suggested that the surface temperature variation for the last 100 years is the result of the superimposition between the global warming and the natural Pacific Decadal Oscillation (PDO) or other oceanic phenomena. The fast warming rate and the intensity as well as the frequency of some extreme events (such as heat waves) in china are consistent with the global counterparts, mainly influenced by the increase of the green-house gases. (6) The model projections have stated that by the end of 21st century, the global surface temperature will possibly increase by 1.0–3.7℃. The increasing amplitude of surface temperature in China will be 1.3–5.0℃. The precipitation will increase by 5%–14% and the extreme events will more frequently occur.

Based on all (ALL) forcing and single-forcing runs from CMIP5 (Coupled Model Intercomparison Project Phase 5) simulations, the present paper examines the anthropogenic influence of greenhouse gases (GHG), anthropogenic aerosols (AA), land use (LU) and combined anthropogenic (Ant) effects on climate change in global arid and semiarid regions. Significant warming is a robust feature over the global land as a response to Ant and GHG forcings, and the warming rate from the latter forcing is two to three times that of ALL forcing results over the past 60 years. AA produces remarkable cooling over the global land surface, whereas LU leads to slight cooling in most arid and semiarid areas. GHG-and Ant-driven increases of precipitation are found in most land areas, especially in arid and semiarid regions. AA and LU produce substantial variation of precipitation over various areas, and current uncertainties are relatively great in AA and LU forcing runs. Ensemble Empirical Mode Decomposition (EEMD) is used to analyze temporal scales of annual temperature and precipitation. The results show that interdecadal and multidecadal variations of temperature and precipitation are attributable to combined natural and anthropogenic forcings in most arid and semiarid regions, where AA dominates variations of both temperature and precipitation on multidecadal timescales. Both GHG and LU have positive effects on multidecadal changes of precipitation over arid and semiarid regions globally. However, the latter significantly prevents multidecadal changes of temperature over arid and semiarid regions of Australia.