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A CoCrCuFeNi high-entropy alloy was successfully welded in this study using fiber laser welding. The effects of the welding parameters on the microstructure and mechanical properties were studied. Three zones were formed: the fusion zone, partial melting zone, and base metal. The base metal exhibited a typical dendrite structure, and the Cu element segregated in the interdendrite. The fusion zone consisted of fine equiaxed crystals and columnar crystals with the same crystalline structure as the base metal. The fusion zone exhibited minimal compositional microsegregation after laser welding. Electron backscatter diffraction results showed that the low-angle grain boundary fraction in the fusion zone increased. Furthermore, some dislocations and dislocation pile-ups were present in the fusion zone, and the densities of the dislocations and dislocation pile-ups were higher than those of the base metal. The hardness of the fusion zone was considerably higher than that of the base metal, while the ultimate tensile strength and elongation values were lower than those of the base metal for all conditions. The ultimate tensile strength and the elongation increased gradually and then decreased with increasing laser power. The maximum ultimate tensile strength exceeded that of the base metal by 90%.

Positive flow characteristic is favorable in design of vertical water wall of large-scale once-through boilers, since it is beneficial for reducing potential temperature differences and thermal imbalance distribution across the water wall. The identification of the critical mass flux (G0) at which the flow characteristic transits from positive to negative is important for design of supercritical boilers with vertical water wall. In this paper, theoretical analysis was performed to investigate G0 under both supercritical and subcritical pressures. A theoretical solution of G0 was derived through thermal-hydraulic models. The impacts of operation parameters and tube structure parameters on G0 were quantified through numerical analysis. The results show that fluid outlet temperature, fluid pressure, tube inner diameter and tube friction factor have significant impacts on G0. G0 decreases as the increase of the fluid outlet temperature and the decrease of the fluid pressure. Under the condition of identical fluid inlet and outlet temperatures, operating pressure and tube length, G0 is proportional to D / λ . With the proposed model, G0 of a 600 MWe supercritical CFB boiler under different loads were calculated and validated.

Ultra-supercritical circulating fluidized bed (CFB) boilers have great commercial potential in large-scale clean utilization of low-quality fuels. Evaporator system is one of the keys in the combination of ultra-supercritical steam cycle with CFB combustion technology. Aiming at examining the thermal-hydraulic characteristic of the evaporator system of the conceptual design of a 660 MWe ultra-supercritical CFB boiler, a mathematical model was developed in this paper. A semi-empirical bed-to-wall heat flux model and a set of empirical correlations available for heat transfer and hydraulic resistance calculation were embedded in the thermal-hydraulic model. By iteratively solving the model, the thermal-hydraulic parameters of the evaporator system at different operating loads, including total pressure drops, mass flux distribution, and metal temperature were obtained. The results exhibit good flow distribution characteristic and low temperature deviations in the evaporator system. The outlet fluid temperature deviation and metal temperature in the evaporator system are both permissible, implying that the conceptual design of the evaporator system of the 660 MWe ultra-supercritical CFB boiler is acceptable.

Deep understanding of flow and heat transfer of supercritical fluids in rifled tubes with non-uniform heating is of great importance for the safety of modern supercritical steam power equipment. In this paper, the heat transfer of supercritical water flowing in a vertical one-side heated rifled tube was numerically investigated. The differences of flow and heat transfer between the circumferentially non-uniform heated rifled tube (NRT) and uniform heated rifled tube (URT) were investigated. The distributions of temperature field, thermophysical properties, axial velocity and turbulent kinetic energy were analyzed. The mechanism of heat transfer improvement of NRT was comprehensively revealed. Results showed that the maximum inner wall temperature in NRT (Tiw,N,max) was 10 K lower than that in URT for the simulation conditions. Both radial and circumferential heat transfers were improved in NRT due to the swirling flow. Under high q/G (ratio of heat flux to mass flux) conditions, the buoyancy effect was weakened in NRT comparing to that in URT. Flow turbulence in boundary layer of y+ > 30 was intensified in NRT, which was crucial for supercritical fluid heat transfer. The positions of Tiw,N,max were not always at the midpoint of the heated side. And a prediction method for Tiw,N,max was proposed.

The design and optimization of gas heater in supercritical carbon dioxide Rankine cycles faces some challenges, among which an urgent one is the effect of thermal boundary condition on the performance of gas heater. This work focused on performance comparison and effects of major operating parameters under two most common thermal boundary conditions regarding to low-grade heat sources, by employing a modified Shear-Stress Transport model where a variable turbulent Prandtl formulation was incorporated. Results show that in the pseudo-critical region thermal boundary condition obviously affected the performance of supercritical carbon dioxide gas heater. Compared with the uniform heat flux condition, at convective boundary condition impairment occurred in both the local enhancement at high mass flux and local deterioration at low mass flux, due to the self-regulation in local heat input. A nearly uniform thermal field under convective boundary condition was achieved by increasing the mass flux of heat source fluid, while increasing the inlet temperature of source fluid was ineffective to that end. Opposite to constant-property fluid heater, flow arrangement dramatically affected axial profiles of local heat transfer coefficient while had a much weaker effect on local heat flux in supercritical gas heater. Temperature distribution of supercritical carbon dioxide along the heater was insensitive to the flow arrangement. Further studies reveal that thermal boundary effect was closely related to the buoyancy effect. Thermal boundary condition has a minimal effect on heat transfer of supercritical carbon dioxide when buoyancy effect is negligible. Under heavy influence of buoyancy, thermal boundary effect was obvious in the form of much weaker local deterioration under convective boundary. Finally, the Jackson Nusselt correlation was found applicable to the prediction of overall heat transfer rate under convective boundary condition, with relative deviations within ±15%.

There has been significant effort devoted to investigating long-term trends in land surface air temperature over mainland China by Chinese scientists over the past 50 years, and much progress has been made in understanding dynamics of the changes. This review highlights research conducted by early Chinese climatologists, and particularly Professor Shaowu Wang from Peking University, with special focus on systematic work that has been conducted since the mid to late 1970s. We also discuss major issues that remain unresolved in past and current studies. The most recent analyses indicate that the country-average annual mean surface air temperature rose by 1.12°C over the past 115 years (1901–2015), with a rate of increase of about 0.10°C decade–1. Temperatures have risen more rapidly since the 1950s, with the rate of increase of more than 0.25°C decade-1. However, the recent increase in temperatures is in large part due to contamination by systematically biased data. These data are influenced by unprecedented urbanization in China, with a contribution of urbanization to the overall increase of annual mean temperatures in mainland China of about one third over the past half a century. If the bias is corrected, the rate of increase for the country-average annual mean surface air temperature is 0.17°C decade–1 over the last 50–60 years, which is approximately the same as global and Northern Hemispheric averages in recent decades. Future efforts should be focused towards the recovery and digitization of early-year observational records, the homogenization of observational data, the evaluation and adjustment of urbanization bias in temperature data series from urban stations, the analysis of extreme temperatures over longer periods including the first half of the 20th century, and the investigation of the observed surface air temperature change mechanisms in mainland China.

Deep understanding of nucleate boiling heat transfer mechanism of saline solution is of great importance for the design and safe operation of steam generation equipment. In this paper, the nucleate flow boiling process of saline solution in a vertical heated pipe was experimentally studied within the concentration range of 0 % ∼ 6 %. In order to realize the visualization, the vertical heated pipe was made of transparent silica glass and a transparent ITO heater was used to provide energy for boiling. The high-speed high-resolution camera was used to capture the vapor-liquid two-phase flow structure. The bubble behaviors such as bubble departure diameter, bubble departure frequency, bubble growth time and waiting time were investigated under different operating conditions. The experimental results showed that the heat transfer deterioration did not occur within the solution concentration of 6% in this work. Under some low heat flux conditions, the heat transfer coefficients of solution can be higher than those of pure water. The reason for this phenomenon can be explained by the different bubble behaviors. Comparing to pure water, the bubble departure diameter of saline solution is bigger and bubble departure frequency is lower. The influences of operating parameters, including concentration, mass flux (200 kg/m2s ∼ 600 kg/m2s), heat flux (30 kW/m2 ∼ 180 kW/m2) and subcooling of fluid (5 K ∼ 35 K), on the nucleate boiling heat transfer coefficients and bubble parameters were comprehensively studied.

Based on a dataset of national reference and basic stations, which have been quality controlled and inhomogeneity processed, updated surface air temperature (SAT) series of the past 67 (1951–2017) and 113 (1905–2017) years for mainland China are constructed and analyzed. The new temperature series show significant warming trends of 0.24°C/10yr and 0.09°C/10yr respectively for the two periods. The rapid regional warming generally begins from the mid-1980s, about a decade later than the northern hemisphere average SAT change. Warming during the period of 1951–2017 is larger and more significant in the northeast, north, northwest and the Qinghai-Tibetan Plateau, and the most significant SAT increase usually occurs in winter and spring except for the Qinghai-Tibetan Plateau where winter and autumn undergo the largest warming. The slowdown of the warming can be clearly detected after 1998, especially for autumn and winter. The effect of urbanization on trends of the region averaged annual and seasonal mean SAT as calculated from the national reference and basic stations has not been adjusted, despite it being generally large and significant. In north China, the increasing trend of annual mean SAT induced by urbanization for the national stations is 0.10°C/10yr for the period 1961–2015, accounting for at least 31% of the overall annual mean warming. The contribution of urbanization to the overall warming of the past half century in Mainland China has also been summarized and discussed referring to the previous studies.

In order to predict heat transfer deterioration (HTD) of supercritical pressure fluid correctly and to investigate the HTD mechanism, the effect of turbulent Prandtl number (Prt) on numerical simulation was theoretically analyzed. Based on such analysis, a new turbulent Prt model (TWL model) was proposed. Numerical simulations of the supercritical pressure CO2 heat transfer in vertical heated tubes were conducted with the proposed Prt model as well as two other previous Prt models and two constant Prt numbers. The performance of the new Prt model was validated by comparing with 14 reported heat-transfer experimental data, especially for the HTD cases. The comparison showed that a better prediction of wall temperature can be achieved with the proposed Prt model in most of the validations, especially for the HTD cases. When HTD occurs, turbulent mixing was restrained in the buffer layer since an “M” shape of velocity profile is formed under the buoyancy effect. The maximum predicted Prt value with TWL model also appears in the buffer layer, while the maximum predicted Prt value with other models appear in the viscous sub-layer. Such Prt profile restrains the turbulent mixing contribution to heat transfer further. Although the turbulent mixing contribution is still several times higher than molecular conduction contribution in the buffer layer when HTD occurs, it’s not strong enough to diffuse energy from near wall region to the bulk region.

To improve heat transfer performance of the gas heater in the supercritical CO 2 Rankine cycle, heat transfer characteristics of supercritical CO 2 heated in Internally Ribbed Tubes (IRT) was experimentally and numerically investigated over a wide range of buoyancy effect. Experiments reveal that for IRT with a geometric parameter of β = 109, serious local heat transfer deterioration did not occur and buoyancy consistently improved heat transfer. IRT showed far superior performance over smooth tubes. Empirical Nusselt correlations were recommended for both upward and downward flows. A numerical model was then developed and verified against experimental data from IRT with different geometries. Further numerical studies on 7 different IRT demonstrate that buoyancy effect relates closely to rib geometries. For IRT with β = 0.48–4, heat transfer to supercritical CO 2 in upward flow was impaired when Bo is around 10 −4 , though the impairment became weaker as β increased. When β reached 16, buoyancy-induced impairment disappeared and Nusselt number increased gradually as buoyancy became stronger. Further increase in β up to 109 didn’t lead to obvious heat transfer enhancement of supercritical CO 2 , indicating that rib geometries play a smaller role in heat transfer than buoyancy for IRT with β > 16. Finally, design strategy for IRT was provided for the optimization of gas heaters.

Heat transfer to supercritical water in vertical Internally Ribbed Tubes (IRT) with various geometries was numerically investigated in a range of p = 25 MPa, Tb = 590 ~ 700 K, G = 100 ~ 1000 kg⋅m−2⋅s−1, q = 200 ~ 800 kW/m2 and q/G = 0.33 ~ 3 kJ/kg. The Shear-Stress Transport k–ω (SST) model was employed to solve the turbulent flow and conjugate heat transfer. In IRT with different rib geometries, buoyancy-induced deterioration of heat transfer did not occur and buoyancy forces continuously enhanced heat transfer at Bo

A new homogenized temperature data set called the China Homogenized Historical Temperature Dataset (CHHTD-V1.0) has been developed, and it includes daily and monthly mean temperature series from 2419 national stations distributed throughout mainland China for the period from 1951 to the present. The inhomogeneities in individual station series were detected using a penalized maximum t-test (PMT) that accounted for the first-order autocorrelation. Detailed metadata information was applied to validate the changepoints caused by changes in local observation systems. Comparative analyses suggested that the quantile-matching (QM) adjustments that accounted for high-order discontinuities led to more reasonable results than the MEAN adjustments for the daily temperature series. Therefore, the QM method was applied to adjust the discontinuities caused by non-climate changes such as changing of observing site, instrumentation and observation environments. The physical consistency among the daily maximum, mean and minimum temperatures (Tmax, Tm and Tmin) was also checked for each station. Based on the new homogenized data set, linear trends in the annual and seasonal temperature series from 1960 to 2014 were calculated. In comparison with the original data set, the homogenized data set improves the geographical consistency of the long-term climate trends over the region. The updated nationwide mean warming rate reached 0.22 °C per 10 years for the Tmax, 0.27 °C per 10 years for the Tm and 0.38 °C per 10 years for the Tmin from 1960 to 2014, which are considerably larger than the previous estimates that were based on the more frequently used networks of a few hundred stations in China.

Ni-CeO2/SBA-15-V catalyst was prepared by the impregnation method with vacuum thermal treatment and used for CO2 methanation reaction. Compared with Ni-CeO2/SBA-15-air catalyst with thermal treatment in air, the reduced Ni-CeO2/SBA-15-V catalyst with vacuum thermal treatment exhibited higher Ni dispersion and smaller Ni particle size. In CO2 methanation reaction, the Ni-CeO2/SBA-15-V catalyst was more active and selective than the Ni-CeO2/SBA-15-air catalyst. The good activity and selectivity of Ni-CeO2/SBA-15-V catalyst should be due to highly dispersed Ni in contact with small CeO2 particles.

Numerical studies on heat transfer to supercritical water in an internally ribbed tube were performed and compared with those in a smooth tube. The Shear–Stress Transport k–ω model was adopted and validated against experimental data from tubes with different geometries. Comparisons between upward and downward flows show that the Jackson buoyancy criterion, which was proposed based on analysis and experiments in smooth tubes, can be used to evaluate effect of buoyancy in internally ribbed tubes. Radial profiles of turbulence and property reveal that in both smooth tube and internally ribbed tube, forced convection heat transfer is mainly influenced by specific heat, and effects of thermal conductivity and viscosity cancel each other out. As heat flux and bulk temperature increased, changes in the integral effect of specific heat resulted in variation in the heat transfer coefficient. The Jackson Nusselt correlation for smooth tubes can also accurately predict heat transfer coefficients of forced convection in an internally ribbed tube. Under conditions of mixed convection, buoyancy had a weaker impact on heat transfer in the internally ribbed tube. Detailed velocities and turbulence explained this weaker effect: the sharp drops in axial velocity gradient and turbulent kinetic energy, which occurred in a heated smooth tube at a radial position similar to the law of the wall region for isothermal flow, did not occur in a heated internally ribbed tube. Moreover, friction factors for internally ribbed tubes were always higher than that for smooth tubes in both forced convection and mixed convection.

Flow and heat transfer of supercritical water (SCW), which experiences dramatic thermophysical property variations and is regarded as Variable Property Fluid (VPF), was numerically studied in vertical upward internally ribbed tubes (IRT). The Shear-Stress Transport k-ω model was employed to solve the turbulent flow and conjugate heat transfer. After validating the model against experimental data from IRT with different geometries, effects of rib geometries on heat transfer to SCW were studied at a pressure of 25 MPa, mass velocity between 600 and 1000 kg/(m2s) and heat flux between 200 and 470 kW/m2. Impact of property variations in IRT is analyzed by comparing SCW flow and Constant Property Fluid (CPF) flow. For the CPF case, IRT always has superior performance over smooth tubes. As for SCW flow, rib geometries play only a small role in both average and local heat transfer under conditions of forced convection. While in mixed convection rib geometries have a significant effect on heat transfer by suppressing the buoyancy effect along the whole circumference to different extents, and by helping SCW recover its large cooling capacity. Internal ribs can more efficiently improve heat transfer to VPF when compared with CPF at the same Reynolds number.

For supercritical pressure fluid upward pipe flow, turbulent mixed convection heat transfer deterioration, which is generally considered to be caused by buoyancy, is often put a deep concern for safety issues. The deterioration is typically characterized by a localized wall temperature peak. Sometimes, there will be another moderate temperature peak after the first one. However, due to the lack of reliable measure method, the understanding of the flow structure for these two localized temperature peaks were still limited. In order to investigate the detailed mechanism for these two peaks and further understand the effect of buoyancy, a numerical study of supercritical pressure carbon dioxide pipe flow mixed convection heat transfer deterioration was conducted in this paper. The SST k-omega model was selected as turbulence model. A variable turbulent Prandtl number model was adopted in the study to improve simulation accuracy. The variation of flow field and turbulence behavior were carefully analyzed. The results show that, the localized wall temperature rise is due to the suppressed turbulence in the near wall region. For the first localized temperature peak, the suppressed turbulence is due to the acceleration of near wall fluid. While for the second one, the restrained turbulence is due to the acceleration of core flow fluid.

Monthly mean instrumental surface air temperature (SAT) observations back to the nineteenth century in China are synthesized from different sources via specific quality-control, interpolation, and homogenization. Compared with the first homogenized long-term SAT dataset for China by Cao et al (2013), which contained 18 stations mainly located in the middle and eastern part of China, the present dataset includes homogenized monthly SAT series at 32 stations, with an extended coverage especially towards western China. Missing values are interpolated by using observations at nearby stations, including those from neighboring countries. Cross validation shows that the mean bias error (MBE) is generally small and falls between 0.45 °C and −0.35 °C. Multiple homogenization methods and available metadata are applied to assess the consistency of the time series and to adjust inhomogeneity biases. The homogenized annual mean SAT series shows a range of trends between 1.1 °C and 4.0 °C/century in northeastern China, between 0.4 °C and 1.9 °C/century in southeastern China, and between 1.4 °C and 3.7 °C/century in western China to the west of 105 E (from the initial years of the stations to 2015). The unadjusted data include unusually warm records during the 1940s and hence tend to underestimate the warming trends at a number of stations. The mean SAT series for China based on the climate anomaly method shows a warming trend of 1.56 °C/century during 1901–2015, larger than those based on other currently available datasets.

Using the reconstructed continuous and homogenized surface air temperature (SAT) series for 16 cities across eastern China (where the greatest industrial developments in China have taken place) back to the nineteenth century, the authors examine linear trends of SAT. The regional-mean SAT over eastern China shows a warming trend of 1.52°C (100 yr)−1 during 1909–2010. It mainly occurred in the past 4 decades and this agrees well with the variability in another SAT series developed from a much denser station network (over 400 sites) across this part of China since 1951. This study collects population data for 245 sites (from these 400+ locations) and split these into five equally sized groups based on population size. Comparison of these five groups across different durations from 30 to 60 yr in length indicates that differences in population only account for between 9% and 24% of the warming since 1951. To show that a larger urbanization impact is very unlikely, the study additionally determines how much can be explained by some large-scale climate indices. Anomalies of large-scale climate indices such as the tropical Indian Ocean SST and the Siberian atmospheric circulation systems account for at least 80% of the total warming trends.

Concentrated salt solutions are used as working fluids in heat exchangers for heavy oil drilling to meet the requirements of environmental protection. Deep understanding the nucleate flow boiling heat transfer mechanism of salt solutions is of great importance for the design and safe operation of modern steam power equipment. In this work, the nucleate flow boiling for NaCl solution and pure water was experimentally studied within the concentration (C) range of 0%–6% in a vertical heated tube. To simultaneously obtain the heat transfer coefficient (HTC) and bubble parameters, the test section was built to be transparent and the energy for boiling was provided by a transparent ITO heater. The bubble parameters, including bubble departure diameter (Dw), bubble departure frequency (f), bubble growth time (tg) and waiting time (tw), were measured in the experiments. A wide range of operating conditions is considered in this study, covering the inlet fluid temperature (Tinlet) between 337 and 365 K, the mass flux (G) between 200 and 600 kg/m2s and the heat flux between 10 and 180 kW/m2. Based on the experimental results, the difference of nucleate flow boiling heat transfer performance between pure water and solutions was compared. It was found that the HTC of pure water was higher than that of salt solutions under the operating conditions of Tinlet 351 K and q > 180 kW/m2, in some cases, it was lower than that of solutions. Dw in the solution is bigger than that in pure water while f in the solution is lower. The corresponding reasons for those heat transfer differences between pure water and solutions were revealed by considering the differences in bubble behaviors, physical properties and mass transfer rate. In addition, the influences of operating parameters on the heat transfer characteristics and bubble behaviors of salt solution during nucleate flow boiling were demonstrated.

Highly dispersed Ni-based catalysts for CO2 methanation have been extensively studied over the last decade. However, a highly loaded Ni-based catalyst always results in a large Ni particle size and poor CO2 methanation activity. In this work, a colloidal solution combustion method was used to prepare a highly loaded Ni&ndash, La2O3 catalyst (50 wt % Ni) with a small Ni particle size and abundant metal&ndash, support interface. The characterizations demonstrated that a Ni&ndash, La2O3 catalyst prepared in this way has a mesoporous structure and a small Ni particle size. Due to the small Ni particle size and abundant metal&ndash, support interface, the highly loaded mesoporous Ni&ndash, La2O3 catalyst exhibits higher activity and selectivity in CO2 methanation compared to the Ni&ndash, La2O3 catalyst prepared by a conventional solution combustion method.

[1] In this study, we bring together different source data sets and use quality control, interpolation, and homogeneity methods to construct a set of homogenized monthly mean surface air temperature (SAT) series for 18 stations in eastern and central China from the late nineteenth century. Missing values are statistically interpolated, and cross validation is used to assess the accuracy of the interpolation approaches. Results show that the errors of interpolation are small, and the interpolated values are statistically acceptable. Multiple homogeneity methods and all available metadata are used to assess the consistency of the time series and then to develop adjustments when necessary. Thirty-three homogeneity breakpoints are detected in the 18 stations, and the time series is adjusted to the latest segment of the data series. The adjusted annual mean SAT generally shows a range of trends of 1.0° to 4.2°C/100 years in northeastern and southeastern China and a range of trends of −0.3° to 1.0°C/100 years in central China near 30°N. Compared to the adjusted time series, the unadjusted time series underestimates the warming trend during the past 100 years. The regional and annual mean SAT over eastern and central China agrees well with estimates from a much denser station network over this region of China since 1951 and shows a warming trend of 1.52°C/100 years during 1909–2010.

This essay discusses the Confucian humanistic values of the combination of "human being" and "benevolence", pointing out that Confucian humanistic values of the combination of "human being" and "benevolence" have introduced high, extensive, benevolent, modest, tolerant spiritual nature, which enabled the Chinese culture to possess a traditional spirit of cultural tolerance, cultural benefit and cultural equality since ancient civilizations. Between native culture and foreign culture, multi-ethnic country in between various e thnic cultures, are due to cultural differences and made into a cultural exchange and collision, will therefore lead to cultural integration or cultural diaphragm. We need a culture inclusive and equitable approach to the understanding of traditional and contemporary ethnic cultural integration experience, but also need to eliminate ethnic conflicts by virtue of the diaphragm caused due to culture. Since ancient times Chinese culture has been the multi-ethnic cultural integration of community of Chinese culture as the main body, this community long-term preservation, not broken, the Chinese nation has always played a powerful role in promoting the spirit. "Toynbee lists the 21 civilizations in world history, which has 20 civilizations have ever been interrupted, only the Chinese civilization has never been interrupted, the Chinese culture is rich and developed continuously in this historic process, this unique historical conditions that other cultures do not have. "(1) (P3) Confucian culture and multi-ethnic cultural fusion took place close relationship, Confucianism Humanism "human being", "benevolence "unity values play an important influence on such C hinese culture and minority cultures together constitute the great tradition and little tradition of mutual benefit, interdependent community. To Study the existence of the multi national cultural fusion community, and understand the relationship between Chinese culture as the main body of culture and minority culture which are equal communicated, mutual effect and inclusive with each other have significant meaning on drawing lessons from history, improving national cultural fusion, realizing the c ultural tradition in the contemporary society, and enhancing national unity in the view of scientific development.

An overview of basic research on climate change in recent years in China is presented. In the past 100 years in China, average annual mean surface air temperature (SAT) has increased at a rate ranging from 0.03°C (10 yr)−1 to 0.12°C (10 yr)−1. This warming is more evident in northern China and is more significant in winter and spring. In the past 50 years in China, at least 27% of the average annual warming has been caused by urbanization. Overall, no significant trends have been detected in annual and/or summer precipitation in China on a whole for the past 100 years or 50 years. Both increases and decreases in frequencies of major extreme climate events have been observed for the past 50 years. The frequencies of extreme temperature events have generally displayed a consistent pattern of change across the country, while the frequencies of extreme precipitation events have shown only regionally and seasonally significant trends. The frequency of tropical cyclone landfall decreased slightly, but the frequency of sand/dust storms decreased significantly. Proxy records indicate that the annual mean SAT in the past a few decades is the highest in the past 400–500 years in China, but it may not have exceeded the highest level of the Medieval Warm Period (1000–1300 AD). Proxy records also indicate that droughts and floods in eastern China have been characterized by continuously abnormal rainfall periods, with the frequencies of extreme droughts and floods in the 20th century most likely being near the average levels of the past 2000 years. The attribution studies suggest that increasing greenhouse gas (GHG) concentrations in the atmosphere are likely to be a main factor for the observed surface warming nationwide. The Yangtze River and Huaihe River basins underwent a cooling trend in summer over the past 50 years, which might have been caused by increased aerosol concentrations and cloud cover. However, natural climate variability might have been a main driver for the mean and extreme precipitation variations observed over the past century. Climate models generally perform well in simulating the variations of annual mean SAT in China. They have also been used to project future changes in SAT under varied GHG emission scenarios. Large uncertainties have remained in these model-based projections, however, especially for the projected trends of regional precipitation and extreme climate events.

Studies on the reconstruction of global mean temperature series are reviewed by introducing three series, HadCRUT3, NCDC, and GISS in details. Satellite data have been used since 1982 in NCDC and GISS series. NCDC series has the most complete spatial coverage among the three by using statistic interpolation technique. The weakened global warming in 2000–2009 as revealed in HadCRUT3 data is possibly caused by the lack of data coverage of this dataset over the Arctic. GISS and NCDC series showed much stronger warming trends during the last 10 years (~ 0.1 °C per 10 years). Three series yielded almost the same warming trend for 1910–2009 ( 0.70–0.75 °C per 100 years). Citation Wen, X., G. Tang, S. Wang, et al., 2011: Comparison of global mean temperature series. Adv. Clim. Change Res., 2(4), doi: 10.3724/SP.J.1248.2011.00187.

Temperature change plays a crucial role in global change sciences. In the past several decades, comprehensive findings have been achieved on temperature change in China for the past 100 years. Several time series have been created to illustrate the averaged surface air temperature for the country. The correlations of these series range from 0.73 to 0.97. It is also achieved in better data quality, wider spatial data coverage, improved homogeneity of time series, and enhanced reliability of findings. The results show an annual mean temperature increase by 0.78±0.27°C per 100 years in China for the period 1906–2005. After prolonging the period till 2007, it is found that 2007 is rated as the warmest year in the past 100 years. Although all the series, except one, reflect temperature changes in the eastern part of China before the 1930s, they represent the general temperature change in most parts of the country after the 1930s. Citation Tang, G., Y. Ding, S. Wang, et al., 2010: Comparative analysis of China surface air temperature series for the past 100 years. Adv. Clim. Change Res., 1, doi: 10.3724/SP.J.1248.2010.00011.

Issues related to the pause of global warming in the last decade are reviewed. It is indicated that: (1) The decade of 1999–2008 is still the warmest of the last 30 years, though the global temperature increment is near zero, (2) Natural factors such as volcanism, solar radiation, ENSO, and thermohaline circulation can have impact on the inter-annual and inter-decadal variability of global mean temperatures. However, it will not mask the global warming trend for a long time, (3) Temperatures of China continue to increase in 1999–2008 with an increment of 0.4–0.5°C per 10 years. Wang, S., X. Wen, Y. Luo, et al., 2010: Does the global warming pause in the last decade: 1999–2008? Adv. Clim. Change Res., 1, doi: 10.3724/SP.J.1248.2010.00049.

At present, 40% of the Earth’s land surface is managed for cropland and pasture (Foley et al., 2005). In developing countries, nearly 70% of people live in rural areas where agriculture is the largest supporter of livelihoods. For China, as such large developing country, the total population accounted to 13 billion with 73% of them pursuing agriculture, and the cropland was 1.3 billion ha in 2006 (CAY, 2007). About 20% of the global population lives in China supported only by 7% of the world’s cultivated land. Although Chinese agriculture has undergone tremendous structural changes over the last decades, the average staple crop productivity has doubled in 25 years while the population increased by 25 % (CSY, 2003), until now, agriculture is still the most important industry for China which can affect food supplies of 13 billion populations. Rice is one of China’s most important staple food crops, and it’s planting area amounted to 27.4% of all food crop area, and it’s production was 37.1% of total food production in China (CAY, 2007). Meanwhile, the production of rice was influenced strongly by climate (Olesen, 2002), so it’s confirmed that the agriculture will be affected greatly by climate change.