Meteorological drought is a precursor of hydrological drought. Understanding the propagation from meteorological to hydrological drought is important for the early warning of hydrological drought. Based on the meteorological and hydrological data from 1901 to 2020 in the upper Yangtze River basin, the characteristics of meteorological and hydrological droughts were firstly analyzed by using the standardized precipitation evapotranspiration index (SPEI) and standardized runoff index (SRI), respectively. The tempo-spatial propagation time from meteorological to hydrological drought for each month were then calculated by the Spearman correlations and sliding window algorithm. The impacts of climate change and human activities on the propagation from meteorological to hydrological drought were finally evaluated by the humidity index (HI) and reservoir index (RI). Results are as follows. Meteorological and hydrological droughts tend to aggravate, and the larger time scale, the longer duration of both droughts. There are obvious spatio-temporal heterogeneity in propagation time from meteorological to hydrological drought, which is long in winter/in northwest, whilst short in spring, summer and autumn/in southeast. The overall drought propagation tends to be faster in spring and summer while it tends to be slower in autumn and winter, and its changes are related to both dry/wet pattern change and intensive hydropower development in the upper Yangtze River basin.

The Planetary Boundary Layer (PBL) is the site of a spatial area of human activity, and the associated environmental problems occurring within the Atmospheric Boundary Layer are closely related to human health and survival. PM2.5 has an important impact on the regional environment and human health. There is a close relationship between the height of the atmospheric boundary layer (Planetary boundary layer height, PBLH) and PM2.5. The analysis of the height of the atmospheric boundary layer and its relationship with PM2.5 has a more comprehensive understanding of PBLH changes in Yunnan province, and has important significance for local air pollution prevention and control. Based on ERA5 PBLH dataset, PM2.5 observation data, temperature, relative humidity and other meteorological observation data, statistic methods were used to systematically analyze the change characteristics and trend of PBLH in Yunnan province from 1980 to 2020, and the correlation between PM2.5 concentration change and PBLH. The results show that affected by the change of direct solar radiation in a day, the PBLH in Yunnan changes steadily at night and fluctuates strongly during the day. The interdecadal variation of the temperature difference between the ground and the atmosphere is in good agreement with the PBLH. From the 2000s to the 2010s, the PBLH in Yunnan showed a steady upward trend. The annual distribution of rainfall, the particularity of geographical location and the difference of weather system make smaller annual PBLH difference in high altitude areas of Yunnan, and the PBLH in dry season is still significantly lower than that in medium and low altitude areas. The PBLH maximum value centers in Yunnan in the four seasons are mostly located from Kunming to Chuxiong, and the percentage change shows an increasing trend. The overall increasing trend is the most obvious in spring, and the spatial distribution difference of the percentage change is the strongest in winter. The low temperature, high humidity and weak wind in the near surface layer cause the rapid decrease of PBLH from 18:00 to 01:00 in the four seasons, causing PM2.5 to accumulate in the near surface layer, and the influence of PBLH on the PM2.5 concentration increases accordingly. The correlation between PBLH and PM2.5 vary with seasons and times. At 02:00 and 08:00, the correlation between PBLH and PM2.5 is basically negative, and the degree of correlation is higher than that at 14:00 and 20:00; Kunming and Qujing, which have more human activities, has a higher negative correlation in summer, autumn and winter.

This paper takes the agricultural economy of Ningxia as an example, integrates the interdisciplinary theories of climatology and economics, quantitatively assesses the differential impacts of historical climate change and extreme events on the agricultural economic output of Ningxia from 1991 to 2020 based on micro-econometric methods, and then the potential impacts of climate change under the SSP3-RCP8.5 and SSP2-RCP6.0 scenarios are estimated, respectively. The results show that both mean temperature and precipitation affect the agricultural economy non-linearly, extreme weather and climate events significantly inhibit agricultural economic growth, and extreme high temperature and heavy drought do not form a “hot-dry” compound hazard impact. The SSP2-RCP6.0 development pathway significantly mitigates the potential negative impacts of future warming relative to the SSP3-RCP8.5 pathway. The results of this assessment reveal the complex impacts of warming and wetting on the agricultural economy in Northwest China, and help to provide a scientific basis for optimal regional adaptation to climate change.

The building sector of China is in urgent needs of low-carbon transition for achieving the national carbon peaking and carbon neutrality goals. Sweden has the second lowest carbon emission intensity in Organization for Economic Co-operation and Development (OECD) countries, counted in the unit of either per total primary energy supply or per GDP, and thus the low-carbon transitional pathways of the Swedish building sector are worthwhile to be investigated. In this paper, the final energy use intensity and the carbon emission intensity are calculated for the operation stage of the building sector in Sweden. The calculation results show that, although the Swedish building sector features a higher final energy use intensity per floor area, 1.3 times higher than that of China, the carbon emission density of the former is only one tenth of the latter. Furthermore, comparisons are made between Sweden and China from a variety of perspectives such as the category of the buildings and the type of the energy use activities. For providing insights on planning the low-carbon transition strategies for the building sector of China, the technological paths and policy frameworks adopted along the low-carbon energy transition of the Swedish building sector are analyzed. Policy suggestions under the scopes of cultivation energy-saving mindset, building electrification, reducing heating demands, and setup of carbon-free heat source are provided for the issue of decarbonization of the building sector of China. Some specific suggestions are given, such as to promote a green lifestyle and to advocate the improvement-oriented design concept of indoor built environment for preventing the rapid increase in energy consumption of buildings, to limit the thermal performance of new buildings and to renovate existing buildings for reducing heating demands, and to promote collection and utilization of surplus heat and biomass fuels for reaching low-carbon heating.

Carbon emissions trading scheme (ETS) has become an important market means to reduce greenhouse gas emissions and an effective policy tool to achieve the goal of “double carbon”. Using airlines as the research object and 2013-2022 as the time window, the difference in differences (DID) model was used to test the impact of China’s pilot ETS policy on the green total factor productivity (GTFP) of airlines. Research has found that even under loose regulations dominated by free quotas, ETS still has a significant effect in curbing aviation carbon emissions and increasing GTFP, especially for low-cost carrier, private aviation, and dual carbon market regulations. For airlines to reduce emissions, a strict benchmark quota allocation method has a better forcing effect than a relaxed grandfather system. ETS mainly enhances airline GTFP by promoting environmental investment and refined management. The research conclusions provide academic reference and quantitative solutions for scientifically evaluating the policy effects of carbon trading pilot projects, improving the total factor productivity of civil aviation, and promoting green development of the industry.

Based on the current situation of China’s coal power and the development trend of carbon market and power market, the impact of carbon allowance allocation rules on power generation revenue of 1000 MW, 600 MW and 300 MW coal-fired units under six carbon prices and three pass-through rates were simulated with economic dispatch model. The results show that the 300 MW units are sensitive to the change in carbon allowance baseline and auction ratio. At the initial period of the coupling between carbon market and power market with carbon price of CNY 50.0 yuan/t, CNY 79.9 yuan/t and a pass-through rate of 20%, if allowances baseline drops to 0.74 t CO₂/(MW∙h) or the auction ratio rises to 50%, 300 MW and 600 MW units will have negative returns. However, when the carbon price and its pass-through rate increase, the negative effect on coal power units caused by the change in carbon allowance baseline and auction ratio is more manageable. The expansion of certified emission reduction ratio has little effect on the improvement of unit revenue, which can be a beneficial supplement to carbon market and be controlled. Therefore, after full consideration of coal power capacity and competitiveness, it is necessary to formulate carbon allowance allocation rules to adapt to the development stages of carbon market and power market, actively promote the coupling of the two markets to pass through carbon costs and cooperate with the offset mechanism to accelerate carbon emission reduction.

To address the problem of unclear boundary, scope and method of carbon emission accounting in China’s transport sector, a combination of top-down and bottom-up approaches was used, through the decomposition of transport modes, to establish a transportation carbon emission measurement model with clear statistical caliber and comparable with international. The CO₂ emissions of China’s transport sector and transport modes in 2019 were measured, and the carbon emission structure and intensity of different modes of transport were analyzed, so as to provide a theoretical basis for the development of carbon emission reduction paths in China’s transport sector. The results show that CO₂ emissions from China’s transport sector in 2019 is 1274 million t, second only to the United States (1788 million t), accounting for 12.42% of the country’s total CO₂ emissions and 14.82% of the world’s total transport CO₂ emissions. The structure of China’s transport carbon emissions is more fragmented, with the share of road transport emissions (79.15%), which is the mainstay of carbon emissions, being lower than that of European countries such as Germany and France and so on (85.19%-96.69%). While the shares of carbon emissions from aviation, waterways and rail transport are higher, at 9.13%, 7.06% and 4.39% respectively. The carbon emission intensity of each mode of transport ranks from the largest to the smallest: aviation, highway, railway and waterway, with the unit conversion turnover carbon emission factors being 899.48, 102.81, 11.33 and 8.65 g/(t∙km) respectively. The Chinese government should guide the transfer of passenger transport from aviation to railway, and insist on promoting the policy of “highway to railway” and “highway to waterway” for freight transport. The unit conversion turnover carbon emission factor does not accurately reflect the carbon intensity of passenger/cargo transport. There is a discrepancy between its value and the actual unit passenger/cargo turnover carbon emission factor value. Taking highways as an example, the value of the unit converted turnover carbon emission factor deviates from the value of the unit cargo turnover carbon emission factor (97.60 g/(t∙km)) and the unit passenger turnover carbon emission factor (45.36 g/(person∙km)) by 5.34% and 126.67% respectively.

With the rapid development of urbanization and motorization in China, urban passenger transport has become a major contributor to carbon dioxide emissions. Under the background of “double carbon”, how to realize the energy conservation and emission reduction of urban passenger transport has become a focus of attention. Based on the data of Beijing, the system dynamics model of carbon emission of urban passenger transport was improved, by considering the influence of road green space and new energy vehicles on the carbon emissions, and the total carbon emissions of urban passenger transport in Beijing from 2011 to 2020 were calculated. Five emission reduction scenarios were proposed based on the carbon peak background, and the emission reduction effects of different scenarios from 2021 to 2025 were estimated. The results show that the private car is the main contributor of urban passenger transportation carbon emissions. The annual carbon sequestration of urban road green space is equivalent to about 28% of the annual carbon emissions of buses. Under single scenario, the carbon emissions of urban passenger transportation in Beijing fails to reach the peak from 2021 to 2025, and the scenario with the best emission reduction effect is “controlling private traffic travel demand”. Under double scenario, part of the combined scenario can make the carbon emissions of urban passenger transportation in Beijing reach the peak before 2030 according to the existing scenario, and the best combined scenario is “controlling private traffic travel demand” and “improving energy efficiency”. Under triple scenario, except for the combined scenarios of “promoting new energy vehicles”, “improving road carrying capacity” and “improving road greening level”, all the other combined scenarios can make urban passenger transportation in Beijing reach the carbon peak before 2030 according to the existing scenario.

Grassland is an important ecosystem carbon pool in China. Several grassland ecological protection projects have been implemented to control grassland degradation and desertification in China. To reveal the impact of ecological management on ecosystem carbon sequestration, four future scenarios of grassland ecological management were set based on the current intensity of grassland ecological managements. Grassland soil carbon sequestration was estimated in China from 2001 to 2030 by using the IPCC Method for National Greenhouse Gas Inventories. The results showed that the mean grassland carbon sequestration was -0.54×10⁸ t CO₂ eq/a from 2001 to 2010 in China. The grassland soil carbon sequestration significantly increased to -1.00×10⁸ t CO₂ eq/a on average during 2011-2017. Under different grassland ecological management scenarios, the grassland soil carbon sequestration is -0.42×10⁸ to -2.00×10⁸ t CO₂ eq/a in China. And grassland soil will sequestrate -5.46×10⁸ to -26.01×10⁸ t CO₂ eq accumulatively from 2018 to 2030. This study provides reference for the formulation of future grassland ecological management policies.

Under the strategic goal of “Carbon Peak and Carbon Neutrality”, the task of improving forest coverage rate and accumulation quantity is made clear, and the carbon sink trade is planned to be brought into the national carbon emission trading market, and the ecological protection compensation mechanism which can reflect the value of carbon sink is suggested to be improved. Since 2012, China has established a national voluntary greenhouse gas emission reduction trading mechanism to record and issue China Certified Emission Reduction (CCER) for emission reduction projects including forestry carbon sink. Due to the challenges of forestry carbon sink projects in development, operation, trading and other stages, and the suspension of voluntary emission reduction related applications by competent authorities in 2017, the development of China’s CCER carbon sink projects was relatively insufficient, and the number of registered projects accounted for only 2%. Based on the perspective of Saihanba CCER project, this paper investigates and analyzes the key technologies, comprehensive benefits, problems and challenges of carbon sink project development, and puts forward policy recommendations to promote the development of forestry carbon sink based on market mechanism.

Adapting to climate change has become one of the important contents of international climate governance. In 2021, the United Nations Framework Convention on Climate Change (UNFCCC) and its Paris Agreement launched the “Glasgow-Sharm el-Sheikh Work Programme on Global Goal on Adaptation (GGA Work Programme)”, which aims to improve the implementation of global adaptation actions, enhance the effectiveness of adaptation actions and strengthen support through the systematic construction of the overall concept of adaptation and the monitoring and evaluation system of adaptation actions. The 27th UNFCCC conference of the Parties held in 2022 proposed a new conceptual technical framework for GGA. However, how to integrate the concepts, data, methods and indicators at the national level into the global adaptation governance system is still lack of systematic scheme design, which hinders the progress of the negotiation of the GGA, reduces the reliability of the conclusions of the Paris Agreement on the matching of adaptation actions and support, and weakens the assessment accuracy of the progress of the implementation of adaptation support provided by developed countries to developing countries. In response to this problem, this study analysis the latest negotiation progress of the COP27 GGA work program, national or group proposals and the technical report of the Adaptation Committee were combed, the key technical difficulties of the concept, indicators and methods of adaptation were identified, and a result that the current proportion of funds to support adaptation actions is less than 30% was determined by analyzing the proportion of adaptation funds in the GEF and technology fields under the UNFCCC mechanism. The study also presents the challenges on existing global adaptation analysis tools in supporting adaptation needs assessment. At the same time, based on the national needs put forward by China’s adaptation strategy, the corresponding solutions and technical paths have been constructed for three main technical weaknesses, namely, the imperfect adaptation concept system, the lack of adaptation action monitoring and evaluation methods and indicator system, and the lack of report specifications that can be used to summarize domestic information and submit to the international community for compliance. All above technical work could strengthen the comprehensive capacity of formulating sound negotiation strategies for China in future.