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Methane (CH4) is the second largest greenhouse gas in the world, and controlling CH4 emissions has climate, environment, safety, and economic benefits. China’s CH4 emissions are relatively large, and conducting medium- and long-term research on CH4 emission control strategies is crucial for the construction of a greenhouse gas emission reduction capacity system in China. Considering the scientific basis of CH4 emission control, this study analyzes the characteristics of CH4 emissions in China and explores the challenges faced by CH4 emission control. The logic of medium- and long-term CH4 emission control is clarified from three aspects: overall management and control idea, action directions of CH4 emission control in various fields, and system architecture of technologies and measures to reduce emissions. Corresponding countermeasures are then provided. The study concludes that China’s medium- and long-term actions regarding CH4 emission control will be constrained by the following problems: (1) large amount of CH4 emissions and differences among sectors and regions, (2) uncertain trends in emissions and specific paths, (3) unclear potentials of technologies and measures for emission reduction, and (4) insufficient capabilities to quantify risks and set targets for emission reduction. The CH4 emission control work of China should be strategically planned based on a long-term perspective, starting from setting overall emission control targets, assigning and implementing responsibilities, consolidating emission reduction capabilities, and enhancing the joint force of management and control. Additionally, institutional, technological, and model innovation should be promoted in a coordinated manner to accelerate the reduction in CH4 emissions.

Current is considered to be a crucial environmental factor in producing extreme waves. The study of nonlinear characteristics in wave–current interactions has been explored, but the role of currents in the more complex interaction processes of double-wave-group focusing is not yet known. Based on our previous research about the nonlinear interactions between wave groups, the impact of uniform current on nonlinear characteristics of double-wave-group focusing is to be investigated in this paper. A fully nonlinear numerical model using the high-order spectral method is developed to simulate various currents interacting with focused bimodal waves. Three ranges of variation exist: strongly opposing current, weakly opposing current, and following current. Unlike the conclusion in the unimodal waves, the asymmetries of the wave crest and that of the wave envelope influenced by currents are not synchronous, which is explained by the changes in the asymmetry of the secondary crests received energy from the currents, in addition to those of the magnitude of the maximum crest and the adjacent secondary crests. When opposing currents enhance to a certain level, a dynamic equilibrium between the energy of waves and currents would be achieved, in which the proportion of the linear components to their own is almost equivalent to that in the non-current state, revealing that the majority of nonlinearity generated by wave–current interaction is blocked at that time. These findings can promote an understanding of nonlinear characteristics due to wave–current interactions. [ABSTRACT FROM AUTHOR]