Since the IPCC put forward the concept of co-benefits in the 1990s, a number of studies have fully confirmed that greenhouse gases (GHGs) emission reduction policies and measures can produce considerable local environmental quality and health benefits. Correspondingly, existing studies have also confirmed that local air pollutants reduction policies and measures also have synergistic benefits for GHGs reduction. Soon after China completed its industrialization, the pressure of local air pollution reached its peak, and at the same time, it faced the tide of international community calling for climate change mitigation, and thus faced the dual pressure of reducing both GHGs and local air pollutants. Therefore, domestic researchers not only paid attention to the one-way co-beneifts evaluation of “from carbon reduction to local pollutants reduction” or “from local air pollutants reduction to carbon reduction”, but also put emphasis on integrated emission reductions. At the beginning of the 21st century, the concept of “co-control” proposed by the US Environmental Protection Agency was introduced into China and warmly embraced. Chinese scholars first defined the connotation of co-control, and believed that co-control was the way to maximize co-benefits. This progress has raised people’s awareness of co-benefits to a new level of “global vision and local action”, and promoted people from passively accepting “co-benefits” to actively seeking “co-control” of both global and local pollutants. It provides an all-round support from epistemology, methodology to practice, for the carbon and local air pollutants co-reduction. On the basis of researches on co-benefits and co-control at home and abroad, Chinese scholars have proposed methods for evaluating co-control effectiveness and planning co-control paths, and verified the scientificity and feasibility of the methods through case studies in multiple industries, cities, and regions. Co-control has become an important national strategy for mitigating climate change and continuously improving the quality of the atmospheric environment. In the process of China’s promotion of the construction of a beautiful China and the realization of its carbon peak goals and carbon neutrality vision, the concept, measures and policies of co-control will play an increasingly important role. In the near future, the co-control objectives will expand from only the atmosphere to the broader eco-environmental system, and the establishment of a co-control governance system will become the key to realize coordination of climate change and ecological environment governance at the macro level.

This study built an evaluation index to quantify the synergistic effect of air pollution control and greenhouse gas emission reduction based on the two-digit four-quadrant map, and established a method to quantify the synergistic effect, sorting out and giving the calculation methods for the emission of major pollutants such as fuel combustion, cement production, and coal-fired power plants, and determining the emission factors and carbon dioxide emission factors of different fuel types and processes. For the evaluation of the “Air Pollution Prevention Action Plan”, the energy structure adjustment and industrial structure adjustment measures were evaluated for the quantified implementation effect of synergy. The results are as follows. The CO₂ emission reduction synergistic effect of all implemented measures to reduce pollutants has a positive synergistic effect, which belongs to pollution emission reduction measures that should be actively encouraged and recommended. The measure to achieve the maximum synergy of CO₂ and SO₂ is to reduce the total coal consumption. In addition, the replacement of coal and oil by electricity, and the replacement of coal by natural gas can also achieve greater SO₂ emission reductions, but their CO₂ emission reductions are relatively small. Eliminating small-scale coal-fired boilers can achieve higher NO₂ and CO₂ emission reduction; eliminating outdated production capacity and dissolving excess capacity also have high synergy effects. The measure of energy consumption reduction has the highest SO₂ and CO₂ synergy evaluation index, followed by fuel substitution measures; the measure of eliminating coal-fired boilers has the highest NO₂ and CO₂ synergy evaluation index, followed by natural gas substitution of coal-fired measures; coal-fired alternative measures has the largest soot and CO₂ synergy evaluation index, followed by energy consumption reduction measures. The implementation of some measures for energy structure adjustment and industrial structure adjustment in the Air Pollution Prevention Action Plan from 2013 to 2017 achieved a reduction in SO₂ emissions of 22.65×10⁶ t, a reduction in NO₂ emissions of 6.56×10⁶ t, and soot emission reduction of 4.69×10⁶ t, while achieving CO₂ emission reduction of 1.46×10⁹ t, having a significant positive synergistic effect.

It's of great significance to conduct research on the integrated control of air pollutants and greenhouse gases in the transportation sector, which will facilitate the realization of integrated management of energy, environment and climate change. In this study, the co-control of air pollutants and greenhouse gases in the transportation sector was chosen as the starting point to carry out future transport demand forecasts for different sub-sectors in China, such as road transportation, railways, civil aviation, inland shipping, and pipelines. The LEAP model was used to build BAU scenario, pollution reduction scenario, green low-carbon scenario, and enhanced low-carbon scenario on emission reduction technologies and policy choices. The simulation results indicate that energy consumption in the transportation sector will peak in 2037 under the enhanced low-carbon scenario and carbon dioxide emissions will peak in 2035. Under the green low-carbon scenario, carbon dioxide emissions will peak in 2040. Besides, it is essential to reduce air pollutant emissions from road transportation sector by taking effective actions, including eliminating old cars, promoting road-to-rail freight, encouraging road-to-waterway freight, and so on. Moreover, some energy structure optimization measures such as the development of hydrogen fuel and bio-jet fuel technology will further reduce pollutant emissions from the transportation sector. To achieve green and low-carbon development in the transportation sector, energy saving and carbon reduction measures, coordinated emission reduction measures should be respectively implemented for passenger and freight transport, and comprehensive policies are considered as an important guarantee for achieving peak goals in energy consumption and carbon emissions.

Waterless printing technology, as one of the important technologies to replace the source of printing industry, is mainly suitable for publication printing, packaging printing and other plate printing, and has been widely used in the world. Taking a printing enterprise in Beijing as an example, the co-benefit evaluation of Volatile Organic Compounds (VOCs) and CO₂ emission reduction after the introduction of waterless printing technology at the enterprise level was carried out, and the data were obtained through field monitoring and open literature to conduct empirical research. The results are as follows. (1) Compared with the baseline scenario, the implementation of waterless printing technology and the installation of terminal treatment facilities can both reduce VOCs emissions, but the implementation of waterless printing technology has better emission reduction effect, and the emission reduction rate is about 60%. (2) After the implementation of waterless printing technology, the CO₂ emission is significantly reduced, but the installation of terminal treatment facilities will increase the CO₂ emission. (3) The source substitution technology represented by waterless printing can realize the synergistic emission reduction of VOCs and CO₂.

Industrial sectors characterized by high energy consumption are considered as important sources of atmospheric pollutants and greenhouse gases (GHGs). In order to facilitate the integrated management, this paper combined with the practice in the industrial sectors in Chongqing implemented by Ministry of Ecology and Environment, took NOx as a case pollutant to calculate and analyze the synergy effect between NOx removal and GHGs emissions in the industrial sectors. The results are as follows. The effect of NOx reduction by applying end-of pipe technology is negative to control GHGs, that is, the removal of 1 t NOx in the industrial enterprises will directly or indirectly increase CO₂ emissions by 1.811 t. The adoption of SNCR technology and the selection of ammonia and other non-urea denitration agents can help to reduce indirect CO₂ emissions from the process and electricity. In 2017, the reduction of NOx in Chongqing’s industrial enterprises increased CO₂ emissions by 525.7 kt, accounting for 0.3% of Chongqing’s total CO₂ emissions from energy activities. If the power emission factor is reduced by 1% or 5%, the synergetic degree of NOx reduction towards GHGs would be raised by 0.9% or 4.3%, respectively, and the synergistic effect of cement manufacturing is improved the most. It is essential to reduce the negative synergy effect of NOx removal technology by decreasing the use of urea and promoting the development of low carbon power.

Gao2008, Crowley2013 and Sigl2015, the three groups of volcanic forcing data are based on polar ice-core reconstruction. Because every reconstruction uses different ice core records and analysis methods, the results are different, which will affect climate models application. This paper combed in detail the differences among the three groups regarding the original ice-core data used for reconstruction, the volcanic signal identification and extraction methodology, and estimation of ice-sheet sulfate deposition; introduced the assumptions made about the season and latitude of unknown volcanic events, and the conversion from polar sulfate deposition flux to stratospheric radiative flux, etc.; and summarized the common problems in the volcano chronologies. By summarizing the impact of these reconstruction uncertainties on climate model application, this study provides additional perspectives on model-proxy comparison and climate impact assessments on historical volcanism.

Coastal areas frequently suffer from flood disasters, which is not caused by a single hazard, but a combination and interaction of multi-hazards. This study sorted out the definitions and mechanisms of compound flood, and systematically summarized the progress of compound flood research from two aspects: statistical model and dynamic numerical model. Compound flood arises from two or three of oceanographic (storm surge, tides, and waves), riverine/fluvial, and pluvial (precipitation leading to direct surface runoff) sources. Studies based on the statistical modeling focus on assessment of joint correlation for multi-variates. It can better understand the spatial and temporal variation of compound flood at a large scale, as well as their relationship with climate factors. The difficulties and future research trends are to construct the nonstationary statistical model of two and more hazards under a changing environment. Studies based on dynamic numerical models require the coupling of hydrology, oceanology, and hydraulic models with meteorological components (tropical cyclones, wind field, pressure field) as important boundary conditions. The modeling process is complex, time-consuming, and requires high computation, but it can clearly describe the evolution process of compound floods, and can be helpful for future scenario analysis. In the future, more attention should be paid to the mechanism of compound flooding in coastal low-lying areas. It is necessary to strengthen the research of long time series model simulation products in combination with climate change factors in the risk assessment of climate change and extreme complex events. In the service of the meteorological and marine forecast, it is proposed to strengthen the research on monitoring and early warning technique, as well as improvement of the dynamic framework, parameterization optimization of physical process, data assimilation, improvement of pattern grid resolution, and optimization of the ensemble prediction scheme. Under the background of global climate change and continuous urbanization, it is urgent to assess the integrated risk of compound flood in coastal areas by considering anthropogenic and climatic factors.

The regional heavy rainfall events (RHREs) are identified by using the Objective Identification Technique for Regional Extreme Events (OITREE) based on the daily precipitation data of 381 stations in the middle and lower reaches of the Yangtze River (MLYR) from 1961 to 2018. There are 245 RHREs in total in the MLYR. The duration of the RHREs in the MLYR is mainly 2 to 3 days, and the longest is 8 days. The cumulative intensity is mainly between (2-4) ×10 ³ mm, and the cumulative area is about (2-5) × 10 ⁵ km². The RHREs in the MLYR mainly occur in summer, especially from June to July. Southeast Hubei, southern Anhui and Northern Jiangxi are the areas where the RHREs occur most frequently in the MLYR. The RHREs in the MLYR has both long-term trends and interdecadal changes. The frequency of occurrence has increased significantly in the past 58 years (0.3 times per decade). The frequency of RHREs and the five indicators all show obvious characteristics of interdecadal variability. From the 1960s to the late 1980s, the RHREs were relatively rare. It showed an increasing trend in the 1990s and reached a peak at the end of the period, after a sharp decline at the beginning of 21st century, there was a slow increase trend.

The dry season is an important period for drought, water ecology and water resources. The changes of runoff in the dry season affect the river ecology and water resources management directly. Based on grid meteorological data and the dry season runoff data of the major rivers in China, the trend of climate change and the evolution characteristics and causes of dry season runoff for major rivers in China from 1961 to 2018 were analyzed. Results indicated that the average temperature in the dry season rose significantly in the whole country, with the northern region warming up earlier and more significantly, and the southern region warming up significantly during in 2001-2018. About 84% of the regions in China had an upward trend of precipitation in the dry season, and about 42.2% of the regions had a significant increase. The precipitation in the dry season increased significantly in the northwest, northeast and southeast of China, while the change in the central part was not significant. The runoff of the middle reaches of the Yellow River and the Haihe River during the dry season decreased significantly. The dry season runoff of the middle reaches of the Yellow River in 2001-2018 decreased by 34% compared with the baseline of 1961-1980, and the Haihe River decreased by more than 80%. The dry season runoff of the upper reaches of the Songhua River and Yangtze River increased significantly. The dry season runoff of the upper reaches of the Songhua River in 2001-2018 increased by 67% and the Yangtze River basin increased by about 16%. The increase of precipitation in dry season led to the increase of runoff in the upper reaches of the Songhua River, Liao River, Huaihe River, Yangtze River and Pearl River. The significant rise in temperature has a significant negative effect on the dry season runoff in the middle reaches of the Yellow River and Haihe River. Human activities are the main factors affecting the decline of runoff in the middle reaches of the Songhua River, Yellow River and Haihe River during the dry season. Although the increase of dry season precipitation in the whole country has a positive effect on alleviating the ecological and water resource problems, the significant increase in human activities and temperature accelerates the consumption of water resources and increases the vulnerability of water resources.

Water resources were the vital factors restricting the sustainable development of social economy and ecological security in the arid region of Northwest China. The Kashgar River and Yarkant River Basins, which originated in the eastern Pamirs, were taken as the study area. Based on the monthly temperature and precipitation data from six meteorological stations and monthly streamflow data from the mountain-pass hydrological stations of the five representative rivers in the eastern Pamirs, the hydroclimate change characteristics and the response of streamflow to changing climate were analyzed. The results are as follow. (1) The precipitation and temperature both showed a significant increasing trend. Except for the Gaizi River, streamflow of all other four rivers showed a significant increasing linear trend. The intra-annual distribution and inter-annual change characteristics of streamflow from different rivers reflected the differences in the main recharge sources. (2) The streamflow in the eastern Pamirs was affected by the combined effects of temperature and precipitation. Annual streamflow dominated by glacier meltwater (the Yarkant River, Kashgar River, and Gaizi River) was mainly affected by summer temperature, and it was significantly positive correlated with the temperature from June to August. While, the streamflow dominated by rainfall and seasonal snow meltwater (the Tizinafu River and Kezi River) was significantly positive correlated with the precipitation from July of the previous year to June at the 0.001 significance level. (3) With the increasing temperature and precipitation, the evaporation of the watershed intensified, and the response of streamflow in the eastern Pamirs to climate change had changed significantly: the positive correlation between streamflow and temperature weakened, and the positive correlation between streamflow and precipitation from previous July to June strengthened.