The urban CO₂ emission peak judgment model based on the conditional judgment function and Mann-Kendall trend analysis test method was constructed to analyze their direct CO₂ emissions and total CO₂ emissions characteristics in the 36 typical large cities of China from 2005 to 2019, and determine whether the comprehensive CO₂ emissions of each city have reached its peaks. In-depth analysis on the characteristics of typical cities at different emission stages was also conducted. The results show that among the 36 typical large cities, Kunming, Shenzhen and Wuhan have reached their peaks, 8 cities are in the plateau period, and the remaining 25 cities have not reached their peaks comprehensively. It is recommended that cities that have not reached the peak of CO₂ emissions should learn the experience from the city that have reached the peak according to their own characteristics, such as adjusting the industrial structure and energy structure, reducing the intensity of carbon emissions, and strengthening the decoupling of carbon emissions from economic growth, so as to achieve the peak of carbon dioxide emissions as soon as possible.

Reducing food wasted is not only a food security issue, but also vital in reducing greenhouse gases (GHGs) emissions and ecological protection. Based on the principles of life cycle, this paper constructs a restaurant food consumption model. Through in-situ and online survey, the main reasons caused the food wasted were systematically analyzed, the average GHG emissions per capita of the restaurant and GHGs emission reductions from reducing catering food surplus were quantitatively evaluated. The results showed that the total amount of GHGs emissions from the restaurant were about 225.28 t CO₂e per year, and the amount of GHGs generated was 2.50 kg CO₂e per capita in terms of catering consumption. Among them, around 97.2 g per capital of food was discarded each meal. The results also revealed that the surplus of food came from the invitation and public consumption was significantly higher than that of ordinary daily meals. Excessive ordering and unexpected taste are main reasons triggering surplus. Young consumers and those with lower education background are more likely to have more food remains. Under the scenario of no food remains, the emission reduction could reach 0.26 kg CO₂e per capital in each meal, which can potentially reduce GHGs emissions by 10.55% of total GHGs emissions from wasted food. Implementing feasible policies is not only for achieving emission reduction goal from food consumption, but also for the sustainable consumption.

The Belt and Road region has widespread population and complex climate types, of which the risks of climate change are yet to be recognized. In this study, we investigated the simulations of the annual extreme monthly temperatures by 31 models of the Coupled Model Intercomparison Project Phase 5 (CMIP5) for 10 sub-regions. The performances of the models for the historical period (1986-2005) were assessed by comparing the simulated and observed probability density functions (PDFs) of the warm/cold month temperatures. A “better-model ensemble” was applied to project extreme monthly temperatures in the middle (2041-2060) and the end (2081-2100) of the 21st century. The models tend to perform relatively better for the cold month than for the warm month temperatures over the historical period. Compared to all-model ensemble/the median, the “better-model ensemble” is more suitable for evaluation of extreme monthly temperatures. As to the changes in extreme warm/cold month temperatures projected under the RCP4.5 scenarios, the inter-model uncertainty is larger over high latitudes than over low latitudes via the “better-model ensemble”. The changes of monthly warm extremes show the largest increase in the Mediterranean Basin and the smallest in Southeast Asia in both the middle of the end of the century. The changes of monthly cold extremes show the largest warming in Northern Europe and the smallest warming in Southeast Asia in both the middle and the end of the century.

The prediction ability of air temperature over China is evaluated in this paper based on the outputs of the Canadian CanESM5 model and the Japanese MIROC6 model participating in the Decadal Climate Prediction Project (DCPP) of the sixth Coupled Model Intercomparison Project (CMIP6). Comparing decadal prediction with historical simulation, both models’ decadal hindcasts show higher prediction skill for surface air temperature (SAT), which proves oceanic initialization improves the prediction skill of SAT in China on decadal scale. The models can capture the variation of annual mean temperature, and the prediction skill of seasonal mean temperature is the highest in autumn and comparatively lower in winter. Although both models have good performances in predicting annual and seasonal mean temperatures in various regions of China, the prediction skills are higher in the southern and western China than the northern China. As the lead time increases, the prediction skills of annual, spring and winter mean temperatures decrease, while those of summer and autumn mean temperature increase. The prediction skills of subregions share the same characteristics with the whole country.

Using the data of total surface solar radiation and sunshine hours of the 95 meteorological stations nationwide, the solar radiation calculation model was established by fitting regression with least squares method. By comparing and analyzing the accuracy of the surface solar total radiation calculation model starting from the daily value and the monthly value, the surface solar total radiation calculation model of different time scales (month scale, seasonal scale, growing season scale and annual scale) of various provinces and regions in China was determined and the distribution and variation characteristics of the empirical coefficients a and b were discussed. The results show that there is no significant difference in the accuracy of the calculation model of the surface solar total radiation among the month, the four seasons, the growing season and the annual solar radiation. The relative error for all models is less than 8.5%, but the calculation model with the daily value as the starting point is better due to the less variability of its coefficients a and b. Based on the daily value as the starting point, the empirical coefficients a and b decreases from the northwest to the south, and their amplitudes decrease from the four seasons to the growing season and then to the annual scale in different regions. According to the empirical coefficients a and b of the annual total solar radiation calculation model of each province, the country can be divided into three regions: the Xinjiang-Gansu-Inner Mongolia region, the Qinghai-Tibet Plateau region and the central-eastern region. The total surface solar radiation calculation model for three regions in each season, the four seasons and the growing season and the annual scale are determined. These models all pass the significance test (p<0.01), and the relative errors of the models are lower than 8.0% in the Qinghai-Tibet Plateau and the Xinjiang-Gansu-Inner Mongolia regions, showing higher simulation accuracy.

Nature-based Solutions (NbS) in combating climate change has become a big concern in international community. The ecosystems of NbS can be divided into forest, grassland, farmland, wetland, ocean and city. The traditional environmental policy instruments were applied to group the policy instruments of NbS in command-and-control regulations, incentive policies, and voluntary participation. Based on the division of policy instruments, the documents were collected and investigated to obtain a policy framework of NbS in China. At the moment, the policy framework is dominated by command-and-control regulations, and also is led by incentive policies with the promotion of voluntary participation. However, there are still a few problems including that NbS is not the mainstream way in addressing climate change, the management system from top to bottom is not sufficient, theory is still not complementary to practice, and other problems like single source of funding, weakness of technology and capacity-building, insufficiency in willingness to participate. To maximize NbS in China, NbS should be included in Nationally Determined Contributions and quantitative goals should be proposed at the next stage. Moreover, it is recommended to mainstream NbS in responding to climate change, to construct top-bottom management system, to establish diversified sources of funding, to strengthen the study on theory to practice and pathway to policy, to promote capacity-building and the willingness to participate.

Nature-based Solutions (NbS) in forestry sector, which are often chosen as the most important approaches to address climate change, have obtained increasing support from governments and scientists, and have been incorporated into relative international climate agreements. Based on an introduction to the concepts, approaches, policies and practices of NbS all over the world, mitigation potential and economic benefits of NbS in forestry sector are reviewed in this paper. Results show that afforestation/reforestation would has higher technical mitigation potential, while reducing deforestation and forest management are more cost-benefit mitigation approaches in forestry sector around the whole world. The practice and scientific research on NbS in forestry in China are still insufficient, but the existing major forestry ecological projects have produced significant emission reduction and economic benefits. It is necessary to further deepen and develop related standards and measurement system construction, research on emission reduction technologies and economic potential, as well as on incentive and guarantee mechanism, and enhancement of public awareness on NbS in forestry sector in China.

With the breakthrough, promotion and application of the fifth-generation mobile communication (5G) technology, the world is gradually entering the era of intelligent interconnection. Based on an energy system analysis model (GCAM), the baseline and intelligent interconnection scenarios were designed and simulated, and the development path of China’s energy transformation was explored under the circumstance that the breakthrough of intelligent interconnection technology is accelerated. Results show that compared with the baseline scenario, the energy system is more efficient under the intelligent interconnection scenario, indicating that the primary energy consumption would be 6.2% lower in 2050; the use of digital and intelligent technology will greatly improve the electrification level of final energy use, which would be 9.6 percentage points higher than that in baseline scenario; energy storage technology, smart grid and distributed energy system will accelerate the development and application of renewable energy, the percentage of which in power generation would be 13.3 percentage points higher than that in baseline scenario; China’s green, low-carbon, safe and efficient energy system will be built earlier, and carbon emissions would drop rapidly after reaching their peak, being 5.6 Gt in 2050 (decreasing by 41.8% compared with 2018), making greater contribution to the global response to climate change.

It is crucial to conduct climate change education for teenagers so that they could appropriately deal with climate change issues in the coming future. To conduct effective climate change education, it requires determining the factors that affecting climate change mitigation behavior and the behavior intention. In this study, we did these analyses based on the theories of the climate change mitigation behavior and the behavior intention of teenagers. The questionnaires have been conducted with 1539 students from nine middle schools of three cities (in Xiamen, Shenzhen and Ningbo). Results indicated that Chinese teenagers situated at a medium level in climate change concern and climate change mitigation behavior, and a low level in climate change knowledge. The past behavior, self-efficiency and the climate change involvement provided significant explanations to students’ mitigation behavior intention. Climate change involvement and self-efficiency showed significant explanation to the climate change mitigation behavior. Furthermore, subjective knowledge of climate change and conscientiousness personality could positively promote climate change mitigation behavior. Based on these findings, more attention should be paid to enhance climate change involvement, knowledge of climate change and self-efficiency for Chinese teenagers in climate change education.

Based on the 165 Nationally Determined Contributions/Intended Nationally Determined Contributions (NDC/INDCs) submitted by countries, the emission reduction targets proposed in NDC/INDCs were taken as the benchmark in this paper. Some factors were considered including the uncertainty of the scope of the emission reduction target, the uncertainty of the carbon intensity reduction target derived from economic scenarios, boundary differences of emission reduction gas type and carbon emission peak constraints, and Monte Carlo simulation were used to quantitatively analyze GHG emissions, uncertainties and their sources of global, regional, and major economies. The results show that by 2030, the total global GHG emissions will reach 62.69 Gt CO₂e, with a 90% confidence interval of 53.17-74.26 Gt CO₂e; since the uncertainty of expected future economy has the most significant impact on emissions, the sources of uncertainty vary greatly among regions. Meanwhile, based on the 2℃ target emission scenario where total emissions by 2050 are 40%-70% lower than in 2010, global GHG emissions need to be reduced by 5.0% % annually from 2030 to 2050. In order to minimize the uncertainty of the global GHG emissions target and continue to work towards the completion of the 2℃ target, countries have to further propose clearer and unified statistical boundaries and more ambitious emission reduction targets when updating their NDCs during the first global stock take.

In a joint effort to address global climate change, the International Maritime Organization (IMO) has considered imposing a regulatory regime on the operational energy efficiency of ships to complement the existing mandatory mechanism on design efficiency. However, the random and uncertain nature of the operational energy efficiency of ships poses a significant challenge to performance regulation. In this paper, a quantile regression model, with dummy variables representing the observation calendar years, is applied to quantify the level, the scale and the skewness of the distribution of the operational carbon intensity performance of international shipping. A rating mechanism is further constructed on this basis, which is able to guide the performance of international shipping as a whole in line with the levels of ambition, whilst being robust to certain individual deviations. This rating mechanism is demonstrated using the bulk fleet of China as a sample, which shows its competency as a systematic solution for scientific evaluation of the operational energy efficiency of ships.

The topic of just transition in international climate governance involves employment issues and people’s livelihood, thus is one of the policy areas that countries are very concerned about. Just transition is now regarded as an important social mechanism to support the actions to address climate change. In recent years, the international community has actively promoted the establishment of a just transition institutional system for climate governance. More and more countries begin to propose and integrate just transition targets and measures into their national climate change strategies or plannings. The trend of mainstreaming just transition topics in the process of international climate governance has brought new opportunities and challenges for China to participate in and lead global climate governance. China should strengthen basic research on this issue; promote the affected groups to receive social justice and achieve a smooth transition in the domestic response to climate change; summarize specific practical experience; make better policies coordination; actively participate in the construction of just transition governance system under the UNFCCC.