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As a vital freshwater resource for one-sixth of the world's population, snowmelt provides great convenience for residents in terms of livelihood and production, agricultural irrigation, and hydroelectric power generation. However, snowmelt can also have an important impact on the formation of surface runoff and the process of soil erosion. In contrast to glacier melt, snowmelt erosion has received relatively little attention in the past. This paper reviewed the generation of snowmelt runoff, the characteristics of erosion and sediment yield during snowmelt, the snowmelt erosion mechanism, and the applications of snowmelt modeling. The published results of sediment yield driven from snowmelt runoff ranged from 1 to 300 t km−2 a−1, with the largest value of 1114 t km−2 a−1. Snowmelt erosion is extremely sensitive to warming climate. With global warming, there is a trend towards earlier snowmelt periods and a significant increase in runoff volume, as well as a significant increase in sediment yield from snowmelt in most of the study cases. Moreover, snowmelt erosion compared to rainfall erosion has more complex mechanistic processes which can be influenced by various factors such as snowfall, freeze-thaw, topography, etc. In particular, the occurrence of rain-on-snow events will lead to more severe soil erosion. In addition, current studies of sediment yield from snowmelt erosion account for a small percentage of snowmelt, and snowmelt erosion modeling is rarely applied in practical studies. In future research, the field monitoring of snowmelt erosion in the context of climate change needs to be further strengthened and the effects of multiple factors on snowmelt erosion need to be investigated. The inclusion of rain-on-snow and specific erosion types in the model will improve the applicability of models under climate change scenarios and in multi-scale environments. This paper is intended to show the achievements as well as the limitations of snowmelt erosion research, while suggesting future research directions that need to be further explored and developed for better understanding and forecasting of snowmelt erosion. [ABSTRACT FROM AUTHOR]

Radon can pose a serious risk on human health. At present, radon has been considered as the second leading cause of lung cancer after smoking. The potential risk of radon exposure in cold regions of Northern Hemisphere is increasing due to climate-induced permafrost degradation. In this paper, we took permafrost regions in the Northern Hemisphere as our study area. We performed an extensive literature review on the Web of Science (WoS), China National Knowledge Infrastructure (CNKI), and Google Scholar (GS). We divided these selected literatures into three groups: Group uranium, Group radon and Group permafrost and tried to reveal the impacts of distribution of uranium deposits/u-rich rocks and permafrost/permafrost degradation on radon concentration/migration in permafrost regions. Based our research, it is evident that uranium deposits or U-rich rocks provides an abundant source of U (Ra) for soils and groundwaters in permafrost regions, resulting in abnormally high concentrations of radioactive elements in soils and groundwaters. As a natural barrier, permafrost soils could screen the radon gas from migrating into underground dwellings and work-space in cold regions. However, permafrost degradation has been extensively observed and this trend is projected to continue under a warming climate. Permafrost degradation and ground ice melting, water exchange, gas emissions and thaw settlement have enhanced the ability of radon migration into dwellings and work space, which substantially endangers human health if long exposed. Our synthesis results also underline that the related research of radon migration and relation in permafrost regions are grossly inadequate and urgently needed. Research priorities include the mechanisms of radon migration in freezing, frozen, thawing and thawed soils/rocks, responses of release of radon sequestered in permafrost soils and radon migration in groundwater systems, among many others, to permafrost degradation. [ABSTRACT FROM AUTHOR]

Urban evapotranspiration (ET) is one of the most important components of water and energy balance, and carbon cycle in urbans. It is also a natural process that is powerful enough to possibly mitigate the negative effects caused by urbanization and global warming. Increasing or regulating urban ET could possibly be a solution to overcome the negative impacts caused by urbanization and global warming. Since 2000, researches on urban ET have been increasing and significant progresses have been achieved. A review of these progresses will certainly further promote the related researches and social practices, however, there is yet no such a review article available. Therefore, this article reviewed almost all the published papers on urban ET over the world, summarized its current progresses, scientific understandings, and forecasted the possible challenges in the future. Results achieved from this review would be helpful to use the power of ET to improve the livability of cities, guide the practices of sponge city construction and low impact development, mitigate the negative effect of urban heat island, and reduce urban carbon emission. [ABSTRACT FROM AUTHOR]

Abstract Global warming has already had a significant impact on social ecosystems. The Tibetan Plateau (TP), which is characterized by a cryosphere, is also recognized to have a profound influence on regional and global climate systems, as well as the ecological economy. Therefore, research on the cryosphere is of significant importance. This paper comprehensively reviews the current status and recent changes of the cryosphere (e.g., glacier, snow cover, and frozen ground) in the TP from the perspectives of observations and simulations. Because of enhanced climate warming in the TP, a large portion of glaciers have experienced significant retreat since the 1960s, with obvious regional differences. The retreat is the smallest in the TP interior, and gradually increases towards the edges. Glacier simulations are comparatively few and still under development. Snow cover is a highly sensitive element of the cryosphere and decreases with large interdecadal variations from the 1960s to the 2010s in general. Simulations of snow cover mostly focus on the mutual feedback between the snow cover anomaly, climate and atmospheric circulation. In situ observations and simulations both indicate that the mean annual temperature of frozen ground increases, causing permafrost thaw and degradation and decreasing the seasonal freeze depth of seasonally frozen ground. Under future climate warming, the cryospheric elements in the TP will continue to diminish on the whole. Studies of climate and the cryosphere are ongoing. To date, the lack of observations is the biggest challenge on the TP, resulting in a divergence of cryosphere dynamics and its simulation being a bottleneck. To overcome these issues, a strategy that combines sets of in situ and remote sensing measurements and improved numerical models is of great importance for achieving breakthroughs with respect to research on the TP cryosphere and its interaction with climate. [ABSTRACT FROM AUTHOR]

Abstract Most estimates of Chinese regional Surface Air Temperatures since the late-19th century have identified two relatively warm periods – 1920s–40s and 1990s–present. However, there is considerable debate over how the two periods compare to each other. Some argue the current warm period is much warmer than the earlier warm period. Others argue the earlier warm period was comparable to the present. In this collaborative paper, including authors from both camps, the reasons for this ongoing debate are discussed. Several different estimates of Chinese temperature trends, both new and previously published, are considered. A study of the effects of urbanization bias on Chinese temperature trends was carried out using the new updated version of the Global Historical Climatology Network (GHCN) – version 4 (currently in beta production). It is shown that there are relatively few rural stations with long records, but urbanization bias artificially makes the early warm period seem colder and the recent warm period seem warmer. However, current homogenization approaches (which attempt to reduce non-climatic biases) also tend to have similar effects, making it unclear whether reducing or increasing the relative warmth of each period is most appropriate. A sample of 17 Chinese temperature proxy series (12 regional and 5 national) is compared and contrasted specifically for the period since the 19th century. Most proxy series imply a warm early-20th century period and a warm recent period, but the relative warmth of these two periods differs between proxies. Also, with some proxies, one or other of the warm periods is absent. [ABSTRACT FROM AUTHOR]

China is the country with the most population in the world, and its climate is extremely diverse due to tremendous differences in latitude, longitude, and altitude, ranging from tropical in the far south to subarctic in the far north and alpine in the higher elevations of the Qinghai-Tibetan Plateau. Accurate assessment of its modern climate change is conductive to addressing global warming threat. Along with the development of Past Global Changes (PAGES) research, the focus has changed from paleo-climate reconstructions to using paleo-data for assessing the present and predicting the future. Previous studies have been devoted to climate change assessment using modern climate observations and simulations. This paper presents a new assessment approach based on the mid-Holocene, which provides a naturally oriented warming that can be compared to modern human-made global warming. A variety of climatic data, including modern observations, paleo-climate records, CMIP5 (Coupled Model Intercomparison Project Phase 5) and PMIP3 (Paleoclimate Modelling Intercomparison Project 3) simulations, as well as lake level models, were applied in this synthesis. Numerical climate classification was introduced to evaluate climate change impacts to Chinese climate zones on various time scales. The results show that winter and summer seasons have different response to the naturally oriented mid-Holocene warming but human-made global warming makes the warming trend appear in all seasons. Temperate and continental dry winter climates expand dramatically during the mid-Holocene warm period; however, the future global warming could have few impacts to Chinese climate zones. Furthermore, the East Asian summer monsoon was strengthened obviously by the mid-Holocene warm climate and strong low-latitude insolation. There is no consistent trend both for the winter and summer monsoon on the background of human-made global warming. In this study, a new benchmark was established based on paleo-climate to evaluate the impacts of human-made global warming. [ABSTRACT FROM AUTHOR]

The late Palaeozoic is a pivotal period for the evolution of terrestrial ecosystems. Generalised warming and aridification trends resulted in profound floral and faunal turnover as well as increased levels of endemism. The patchiness of well-preserved, late Permian terrestrial ecosystems, however, complicates attempts to reconstruct a coherent, global scenario. In this paper, we provide a new reconstruction of the Bletterbach Biota (Southern Alps, NE Italy), which constitutes a unique, low-latitude record of Lopingian life on land. We also integrate floral, faunal (from skeletal and footprint studies), and plant–insect interaction data, as well as global climatic interpretations, to compare the composition of the 14 best-known late Permian ecosystems. The results of this ecosystem-scale analysis provide evidence for a strong correlation between the distribution of the principal clades of tetrapod herbivores (dicynodonts, pareiasaurs, captorhinids), phytoprovinces and climatic latitudinal zonation. We show that terrestrial ecosystems were structured and provincialised at high taxonomic levels by climate regions, and that latitudinal distribution is a key predictor of ecosystem compositional affinity. A latitudinal diversity gradient characterised by decreasing richness towards higher latitudes is apparent: mid- to low-latitude ecosystems had the greatest amount of high-level taxonomic diversity, whereas those from high latitudes were dominated by small numbers of higher taxa. The high diversities of tropical ecosystems stem from their inclusion of a mixture of late-occurring holdovers from the early Permian, early members of clades that come to prominence in the Triassic, and contemporary taxa that are also represented in higher latitude assemblages. A variety of evidence suggests that the Permian tropics acted as both a cradle (an area with high origination rates) and museum (an area with low extinction rates) for biodiversity. [ABSTRACT FROM AUTHOR]

Floods do have multiple aspects: they are integral phenomena by nature. In this paper we deal with the meteorological aspects, which need to be adequately understood in order to understand the occurrence and development of floods. This holds the more as different meteorological environments and accompanying mechanisms can result in different types of heavy precipitation and so in different flood responses. In this paper, the meteorological aspects of floods are described from the perspective of a precipitation event. The characteristics, the categorisations and the ingredients of the storm systems are presented. The influences of global warming on heavy precipitation events will be discussed as well. The sequence of these aspects reads as a logical succession of the distinct topics of the meteorological aspects of a heavy precipitation event. Since floods commonly have a profound impact on environment and society, the understanding of the meteorological aspects is a first and necessary step in a challenge of dealing with floods. The ultimate goal of this step is to diminish the harmful consequences of floods as adequately as possible. [ABSTRACT FROM AUTHOR]

The Early 20th Century Warming (ETCW) in the northern high latitudes was comparable in magnitude to the present-day warming yet occurred at a time when the growth in atmospheric greenhouse gases was rising significantly less than in the last 40 years. The causes of ETCW remain a matter of debate. The key issue is to assess the contribution of internal variability and external natural and human impacts to this climate anomaly. This paper provides an overview of plausible mechanisms related to the early warming period that involve different factors of internal climate variability and external forcing. Based on the vast variety of related studies, it is difficult to attribute ETCW in the Arctic to any of major internal variability mechanisms or external forcings alone. Most likely it was caused by a combined effect of long-term natural climate variations in the North Atlantic and North Pacific with a contribution of the natural radiative forcing related to the reduced volcanic activity and variations of solar activity as well as growing greenhouse gases concentration in the atmosphere due to anthropogenic emissions. [ABSTRACT FROM AUTHOR]

Recent research shows increasing decadal ice mass losses from the Greenland and Antarctic Ice Sheets and more generally from glaciers worldwide in the light of continued global warming. Here, in an update of our previous ISMASS paper (Hanna et al., 2013), we review recent observational estimates of ice sheet and glacier mass balance, and their related uncertainties, first briefly considering relevant monitoring methods. Focusing on the response to climate change during 1992–2018, and especially the post-IPCC AR5 period, we discuss recent changes in the relative contributions of ice sheets and glaciers to sea-level change. We assess recent advances in understanding of the relative importance of surface mass balance and ice dynamics in overall ice-sheet mass change. We also consider recent improvements in ice-sheet modelling, highlighting data-model linkages and the use of updated observational datasets in ice-sheet models. Finally, by identifying key deficiencies in the observations and models that hamper current understanding and limit reliability of future ice-sheet projections, we make recommendations to the research community for reducing these knowledge gaps. Our synthesis aims to provide a critical and timely review of the current state of the science in advance of the next Intergovernmental Panel on Climate Change Assessment Report that is due in 2021. [ABSTRACT FROM AUTHOR]