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Instrumental data from the pre–Industrial Revolution period are important to -understand climate change. In this paper, the observations made by the French missionary J. Amiot in present-day central Beijing during 1757–62 were processed and analyzed. The observations represent the earliest continuous dataset of meteorological records found in China that have been digitized recently. Comparisons between the Amiot annual temperature range and extreme values with modern observations showed that the observations were read at approximately 0800 and 1500 local solar time (LST) in a well-ventilated outdoor site. The daily maximum, minimum, and mean temperatures (T-max, T-min, and T-mean, respectively) during 1757–62 were determined by examining the relationship between temperature at 0800 and 1500 LST and T-max, T-min, and T-mean in modern reference series. Nearly 260 years ago, Beijing's climate was typical of an inland temperate monsoon zone with annual T-mean, annual mean T-max, and annual mean T-min being 11.5°, 17.8°, and 6.1°C, respectively; further, the temperatures did not vary considerably from the 1951–1980 temperatures, but differed evidently compared to relatively recent decades (1981–2020). The difference was larger than the magnitudes of global and regional temperature changes. Thus, climate warming since the pre–Industrial Revolution period in the urban areas of Beijing has dominantly occurred over the last four decades. Uncertainties related to the thermometer and observational conditions 260 years ago and the interpolation method used have also been discussed in this paper. [ABSTRACT FROM AUTHOR]

Impending climate warming is expected to influence plant growth and distribution, and the distribution range limit of tree species is extremely sensitive to climate change. However, synchronous comparisons of responses of different tree species with overlapping ecological niches to climate at their distribution range limit in the same region have received little attention. In the present study, we assessed the discrepancy in radial growth responses of two dominant oak species to climate at their distribution range limit (southern range limit for Quercus mongolica, northern range limit for Quercus variabilis) in Beijing, China. Furthermore, growth-climate relationships were examined using linear mixed-effects models, and growth trends up to the year 2100 were forecast based on future climate scenarios (RCP2.6 and RCP8.5). Our results indicated that there were no significant differences in the growth response to climate between Q. variabilis at its northern limit and Q. mongolica at its southern limit, and the growth of the two tree species was positively correlated with the minimum temperature and negatively correlated with the climatic moisture deficit of autumn. However, the growth response to climate variables varied at different sites. Additionally, the model forecast showed an increase in radial growth of Q. variabilis at its northern limit and Q. mongolica at its southern limit up to the end of the present century. [ABSTRACT FROM AUTHOR]

Black carbon (BC) is one of the most important climate pollutants due to its strong positive radiative forcing on the climate system. However, long-term observation of BC is inadequate, and its trend remains unknown at both regional and global scales. In this study, using quality-controlled ground-based black carbon observations at 34 stations, the climatology of BC mass concentration during 2006–2017 in China was evaluated for the first time. The national annual average BC concentration was 3534 ng/m3, and the concentration exhibited large spatial variation, from a minimum of 272 ng/m3 to a maximum of 10,228 ng/m3. Significant seasonal variations were also observed. The peak BC concentration (4763 ± 3380 ng/m3) occurred during winter, followed by autumn (3752 ± 2623 ng/m3) and spring (3022 ± 2121 ng/m3). The lowest BC concentration occurred in summer (2583 ± 1780 ng/m3) due to decreased emissions, wet removal by precipitation, and diffusion induced by strong turbulent mixing. Additionally, the diurnal variability at about 80% of the stations in China showed a bimodal pattern. Daily maximum BC concentration during 0000–0600, 0600–1200, 1200–1800, and 1800–2400 local solar time accounted for 0, 41, 12, and 47% of the total, respectively. In particular, the diurnal and monthly variations in BC were explicitly analyzed at seven baseline stations. Surface BC has exhibited a significant declining trend across China, which is partly corroborated by the increase in single scattering albedo during the same period in Beijing. Also, the BC radiative forcing at the top of the atmosphere has declined at the rate of − 0.9 ± 0.1 W/m2/10 years over China, which differs from with the trend in the simulation using the CMIP6 emission. The decreasing BC has led to a larger reduction rate in atmospheric heating (− 3.7 ± 0.4 W/m2/10 years), implying a less stable atmosphere that facilitates the dispersion of air pollutants. The declining BC burden implies for both the air quality in China and regional climate change. [ABSTRACT FROM AUTHOR]

This study is responding to the recommendation made by IPCC’s fifth Assessment Report on establishing a standard for measuring and reporting climate risk and vulnerability. It exemplifies the assessment of urban vulnerability to climate change by an integrated approach. The results indicate that Beijing is highly exposed to multiple climate threats in the context of global climate change, specifically urban heat waves, urban drainage floods and drought. Vulnerabilities to the climatic threats of heat waves, drainage floods and droughts have increased by 5%–15% during the period of 2008–2016 in Beijing. High vulnerabilities to both heat waves and drainage floods have been observed in the urban downtown area and high vulnerability to droughts have been observed in the outskirts. This vulnerability assessment, which addressed climatic threats, provides a holistic understanding of the susceptibility to climate change that could facilitate adaptation to climate change in the future. The developments of threats like flooding, heat waves and droughts are analyzed separately for 16 districts and an integrated vulnerability index for all of Beijing is provided as well. [ABSTRACT FROM AUTHOR]

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Wetlands, and especially their littoral zones, are considered to be CH4 emissions hotspots. The recent creation of reservoirs has caused a rapid increase in the area of the world’s littoral zones. To investigate the effects of water depth and water level fluctuation on CH4 fluxes, and how these are coupled with vegetation and nutrients, we used static closed chamber and gas chromatography techniques to measure CH4 fluxes in the littoral zone of a large reservoir near Beijing, China, from November 2011 to October 2012. We found that CH4 flux decreased significantly along a transect from open water to dry land, from 3.1 mg m−2 h−1 at the deep water site to approximately 1.3 mg m−2 h−1 at the shallow water site, and less than 0.01 mg m−2 h−1 in the non-flooded area. Water level influenced CH4 flux by affecting soil properties including soil redox potential, soil carbon and nitrogen, and bulk density. The largest emission of all was from the seasonally flooded site after a flooding event (up to 21.1 mg m−2 h−1), which may have been caused by vegetation decomposition. Submerged sites had greater emissions, while the driest site had lower emissions. Immediately after the monthly measurements had been made, we removed the aboveground vegetation to enable an assessment of the gas transportation per unit of biomass. Removal of biomass decreased emissions by up to 53%. These results indicated the dominant effect of water depth on CH4 flux through effects of soil conditions, plant species composition and distribution. This study suggests that temporally flooded wetlands, including littoral zones, contribute significantly to the global CH4 burden. However, the current challenge is to capture their spatial extent and temporal variation in the fluxes. [ABSTRACT FROM AUTHOR]