By now, EU, China, Japan, Korea, Canada, together with South Africa etc., have announced their carbon or GHGs neutrality targets. And it is also very possible that United States will announced its carbon neutrality target. All these countries’ CO₂ emission accounts for around 70% of global emission. Because these countries are technology and economy dominating countries, it is possible that the global will reach carbon neutrality by 2050. Carbon neutrality by 2050, is matching with the emission pathways under the Paris Agreement targets, even with its 1.5℃ warming target. Researches show that it is feasible to make carbon neutrality by 2050, and there is strong need for innovative technologies, and there will be technology and economy competition in future to make their pathways towards to the carbon neutrality targets.

Under the 1.5℃ target of the Paris Agreement and China’s goal of achieving carbon neutrality before 2060, a comprehensive energy-economy-environment system model has been established to explore China’s additional emission reductions, sector contributions and key emission reduction measures to achieve 1.5℃emission pathway based on 2℃ emissions scenarios. The results show that the 1.5℃ scenario requires carbon emissions to be reduced to 0.6 Gt CO₂ by 2050, total primary energy consumption to peak at 6.8 Gtce in 2045, and the energy structure to be significantly optimized, with non-fossil energy accounting for 67% and coal proportion dropping to 16%. Compared with 2℃, 1.5℃ requires an additional cumulative emission reduction of 38.0 Gt CO₂, and the additional emission reduction mainly comes from the power sector. In terms of emission reduction measures, the additional emission reduction mainly comes from new low carbon energy and Bioenergy with Carbon Capture and Storage (BECCS) technology. The emission reduction measures are different by sector. The power sector relies more on BECCS and other emission reduction technologies to achieve a relatively large negative emission, which is the key to achieve the 1.5℃ target path. The industrial sector still relies heavily on energy efficiency. The construction and transportation sectors are more dependent on the adjustment of terminal energy structure in which hydrogen energy plays a greater role.

To clarify the challenges and potentials faced by the transition of the power system under the constraint of the climate change agreement to form an effective key, this paper starts from the impact analysis of climate change target on electricity demand, sorting out the pathway selection of power system transition systematically, then summarizes the issues related to power system transition process closely including the coal-fired power drop out, the renewable energy integration, the grid optimization, and proposes policy suggestions at last. The scale of coal-fired power needs to decline rapidly, the high-share integration and long-distance transmission of renewable energy generation will become the most significant features for the power system in the future, gas-fired power will assume greater responsibility than it is now, and nuclear power needs to abandon disputes to accelerate its development under the constraints of temperature rise target. Accelerating the improvement of market-oriented mechanisms, controlling the scale of coal-fired power capacity strictly, focusing on improving energy efficiency, coordinating and strengthening flexible resource management, and optimizing cross-regional load management should be the concerns of regulatory agencies in the future.

To limit global warming well below 2℃, transport sector needs to be deeply decarbonized in China. This paper presents a review analysis of current greenhouse gas emission and future trend of transport sector, and a discussion about the low carbon pathways based on the potentials and costs of different mitigation strategies. Greenhouse gas emissions from transport sector will keep increasing rapidly in future several years. Road transport remains the highest proportion, while emission from civil aviation enjoys the most rapid growth. The available mitigation options can be categorized into four groups: structural changes including new customer behavior and demand, disruptive technologies including autonomous vehicles, alternative fuel technologies and fuel economy improvement. To decarbonize transport sector, stricter fuel economy standards should be implemented, alternative fuel vehicles should be prompted and feasible measures should be adopted to lead the structural transition.

As the largest coal power provider in the world, China needs to give more consideration to assess the stranded coal-fired assets, which caused by meeting the Paris Agreement’s long-term goals of capping global warming rise to 2℃ by the end of the 21st century. With an integrated carbon lock-in curves (CLICs) approach, China’s stranded coal power assets were identified under different coal power capacity expansion scenarios (no additional, 200, 300 and 400 GW new coal power units). From a “top-down” perspective, the carbon emission allowances were estimated for China’s coal power sector under 2℃ climate target. From a “bottom-up” perspective, the cumulative carbon emissions of coal power units were calculated, based on the high-precision data of coal power unit in China. Then “interaction up and down” to screen out stranded coal power units. Stranded value of coal power was estimated based upon a cash flow algorithm, with sensitivity analysis on key factors. The counterintuitive finding is, if stabilizing coal power capacity during 2020-2030, China will only incur a sizeable yet acceptable stranded loss around CNY 382 billion, however, continued increase of another 200-400 GW coal power would significantly enlarge the loss to 3.7-8.2 times. Therefore, during the Fourteenth Five-Year Plan period, in order to avoid missing the best time to reduce CO₂ emissions, it is necessary to establish peak coal power capacity and strictly control new coal power plant.

In this paper, a mesoscale numerical model coupled with a single-layer urban canopy model (WRF/UCM) was used to conduct sensitivity tests on eight roof cooling schemes with different albedo and greening ratio to simulate the impact of different cooling roof schemes on the urban thermal environment of Yangtze River Delta urban agglomeration in summer of 2013, and the influence mechanism was also analyzed. The results show that: there is a strong linear relationship between the mitigation effect of different cooling roof schemes on urban agglomeration thermal environment and the roof parameters, and the mitigation effect on heat-wave is better than that on normal summer under the same scheme. During heat wave, the cooling degree days of HR4 (albedo of 1.0) and GR4 (green fraction of 100%) are reduced by 14.7% and 10.9%, respectively, which saves more energy than normal summer. Heat-wave can enhance the intensity of heat island, and the high albedo roof scheme can reduce the heat island by 1.36℃ in the daytime. On average, the cooling effect of high albedo roof and roof greening increased by 38.5% and 34.9%, respectively, and the humidification effect increased by 29.5% and 21.9%, respectively. This is mainly because the former can reduce more net radiation flux in heat wave, and the latter can release more latent heat flux in heat wave. In addition, the cooling effect of dense urban grid areas is better than that of scattered urban areas. The average cooling range of Changzhou area in urban agglomeration is 32% higher than that of Hangzhou area.

Based on the Coupled Model Intercomparison Project Phase 6 (CMIP6), the paper evaluates the performance of the state-of-the-art climate model BCC-CSM2-MR in simulating the Arctic sea ice and the Arctic climate using sea surface temperature and sea ice density data from the Hadley Center and the reanalyzed data from National Center for Environmental Prediction and National Center for Atmospheric Research and further projected their potential changes in a future warmer world under Shared Socio-economic Path (SSP). The results show that the BCC-CSM2-MR model can better reproduce the multi-year average spatial distribution of Arctic sea ice concentration, near-surface atmospheric mean temperature and sea surface temperature. However, the simulation has a certain deviation from the observation of the atmospheric temperature in the Arctic, which possible leads to differences in the simulation of sea ice in the corresponding areas. In the 21st century, the Arctic sea ice range is projected to decrease continuously, with a significant reduction in September and a relatively weaker trend in March. In March, the atmospheric temperature would show a consistent increase over most of the Arctic except the North Atlantic. The increasement of atmosphere temperature is weaker in September than that in March. Unlike the atmosphere temperature, the sea surface temperature would both increase in March and September in most parts of the Arctic except the Labrador Sea. The increasement of sea surface temperature is much greater in September than that in March.

As a leading country in coal chemical technology, a huge number of coal chemical factories are at stages of operating, construction and proposal to administrative system in China. This causes huge problems of CO₂ emissions and water demand. CO₂-enhanced deep saline water recovery (CO₂-EWR) technology can provide large-scale CO₂ mitigation and additional water recovery, especially in coal rich and water scarcity areas. The combination of CO₂ from industrial separation processes in the coal chemical industry and CO₂-EWR technology can provide low-cost opportunities to solve the CO₂ mitigation-water shortage nexus. The study firstly establishes a model of Integrated Techno-Economic Assessment Method for CO₂ Capture, Utilization and Storage (ITEAM-CCUS) in industrial scale which includes source-sink matching, techno-economic assessment, CO₂ emissions assessment, and storage site suitability evaluation. Then assess high concentrations of CO₂ emissions which is captured from China’s coal chemical factories of 2018, source-sink matching, and the range of cost and emissions reduction potential of full chains CO₂-EWR projects. The basic evaluation results are that most of the source-sink couplings distribute in dry areas including Northwest China, North China, northern, etc. Annual high concentrations of CO₂ emissions respectively is 190 Mt and 1726 Mt assessing by the actual production in 2018 and the total capacity of coal chemical factories; the annual cumulative CO₂ emission reductions are 160 Mt and 1569 Mt with levelized cost less than 200 CNY/t CO₂, and the corresponding saline water production are 241 Mt and 2353 Mt, respectively. Therefore, CO₂-EWR technology can be essential to low-carbon and sustainable development of the coal chemical industry in China, and may provide low-cost opportunities to spread the large-scale deployment of CCUS technologies in China.

In this paper, a numerical model was developed based on the design capacity and operating time of equipment to grasp the carbon emission situation and establish production carbon emission inventory of cement companies in the case of actual production data is unknown. The accounting model of CO₂ was established with 59 typical cement clinker production lines in the Beijing-Tianjin-Hebei region as statistical samples, and the production time as correction factor. Meanwhile, the relation of design capacity with actual production and specific energy consumption was fitting by Eviews respectively. The results showed that the relative error between the total output calculated by model of cement clinker in the Beijing-Tianjin-Hebei region in 2018 and the statistical data released by Digital Cement Network is 7.81%. In addition, the direct CO₂ emission coefficient was 0.93 t CO₂/t C, which was 7.27% difference with the domestic average data. The constructed accounting model is in good agreement with actual production. More importantly, this numerical model can be used to establish the CO₂ emission inventory of all cement enterprises in the region from bottom to up to achieve inventory grids with high spatio-temporal accuracy. Moreover, the numerical model could lead to more targeted carbon monitoring and emission reduction policies by compared with the data obtained from existing satellite remote sensing detection and mobile monitoring equipment.

China put forward the goal of 2060 carbon neutrality in the general debate of the 75th UN General Assembly. Existing researches pay less attention to carbon neutrality or lack of understanding of its international situation. This paper presents a review of the target contents and policies and regulations documents of 31 carbon-neutral commitment countries in the world. By analyzing the contents and trends of carbon neutrality documents in various countries, it is found that carbon neutrality is becoming an important part of global climate governance, and developed countries/regions such as the European Union are important leaders in carbon neutrality action. High emission countries including the United States and India shall join the international community of carbon neutrality. The international community shall carefully design the strategies and policy pathways towards carbon neutrality, and include the carbon neutrality vision in international climate governance. China should strengthen the research on carbon neutrality strategies in key countries, draw lessons from the technological path, policy measures and advanced experience in low-carbon recovery and social fair transformation of the country. Follow-up researches should be carried out on international carbon neutrality actions for fast identification of climate governance opportunities and response to changes in the international climate governance situation.

Trilateral Cooperation is a new model of international cooperation that complements the conventional South-South and North-South Cooperation models. Because of the advantages of fully mobilizing multiple resources, strong complementary effects of developed countries and emerging countries, and flexibility, Trilateral Cooperation has now gained the attention and participation of more countries and international organizations. 838 Trilateral Cooperation projects have been implemented worldwide in 2016, and 2/3 of the members of the Development Assistance Committee of the Organization for Economic Development and Cooperation (OECD) are participating in Trilateral Cooperation projects to varying degrees. Among them, Germany, Japan, Spain and the United States are involved in the largest number of projects. Among the emerging donors, Chile and Mexico are the countries with the highest participation in Trilateral Cooperation projects. Currently, the implementation period of trilateral projects is short, the funding size of projects is small, and 29% of projects refer to green goals. Although there are currently few cases of climate change Trilateral Cooperation, 32 developing countries and 5 developed countries have expressed interest in Trilateral Cooperation on climate change by the end of 2018. Due to its late start, climate change Trilateral Cooperation is currently facing problems such as insufficient funding, complicated communication and coordination processes, and high collaboration costs. China should actively explore Trilateral Cooperation on climate change, promote resource integration of South-South Cooperation, Trilateral Cooperation and other multilateral and bilateral cooperation in various sectors, and should enhance project management to improve effectiveness and impact.