As the world’s largest developing country, China is facing the serious challenge of reducing carbon emissions. The objective of this study is to investigate how China’s aging population affects carbon emissions from the production and consumption sides based on an improved Kaya model. The advantage of the Kaya model is that it links economic development to carbon dioxide generated by human activities, which makes it possible to effectively analyze carbon emissions in relation to the structure of energy consumption and human activities. Based on different energy consumption structures and technological innovation levels, a threshold effect model is constructed. The results show that: (1) There is an inverted U-shaped curve relationship between population aging and carbon emissions in China. (2) Energy consumption structure and technological innovation thresholds can be derived for the impact of population aging on carbon emissions, with thresholds of 3.275 and 8.904 identified, respectively. (3) Population aging can reduce carbon emissions when the energy consumption structure does not exceed the threshold value. (4) There is no significant intervention effect of technological innovation on the relationship between population aging and carbon emissions. Based on the research results, some countermeasures and suggestions to reduce carbon emissions are proposed.

In the requirement of the “double carbon” goal, China has confronted the lack of a driving force for the low-carbon transformation of socioeconomic development, which requires a comprehensive law and strategy support system for supporting a circular economy. In this study, a framework associated with a multi-level quantitative index system associated with legislative support for a circular economy (MILC) through the entropy TOPSIS method was developed. It can not only reflect the legal support for a circular economy in four areas based on the “3R” principle, but also respond to the process of environmental law improvement dynamically. The legislative support effect can be applied and analyzed in China’s circular economy for the period from 2009 to 2022, which can respond to the process of legal improvement on the environment dynamically. The obtained results show that China’s circular economy and its rule-of-law guarantee system are still facing many challenges, such as the low systematic degree of legalization for industrial development, unmatched supporting legal system, and backward concepts and consciousness of circular economy legalization. Various suggestions according to the identification of the importance of a legal support system for the circular economy were obtained, which can not only encourage a reduction in resource consumption and carbon reduction from the view of systematic legalization, but also promote socioeconomic transformation to match the goal of “double carbon”.