Developing a factorial hypothetical extraction model for assessing composite effects on cutting national carbon emission intensity

China has pledged to reach its carbon emission peak by 2030 and achieve the neutrality around 2060’s. Cutting the national carbon emission intensity (CI) is conducive to achieve these ambitions. To reduce China's CI, simultaneous implementation of efficient countermeasures may come at the expense of system health. Evaluation of composite effects of multiple mitigation countermeasures is critically desired. Factorial analysis can help analyze all the combinations comprehensively and quantitively. The hypothetical extraction method is proposed to measure the importance of a sector within a national economy. Such that countermeasures for seven extracted sectors were established. Emission reduction-related sectors include nonmetal products, metallurgy, electricity-generation, wholesale and retailing, leasing and commercial services, other services and agriculture sectors. Then a seven-factor factorial design involving 128 scenarios is developed to explore the composite effects and the implied interactions of multiple factors (i.e., countermeasures). Results show that despite of the positive effects on emission abatement, lessening the production scale of the electricity-generation sector brings negative impact on system sustainability and robustness. A tradeoff between CI reduction and system health will be instigated by limiting the production scale of metallurgy sector or expanding the production scale of the wholesale and retailing sector. Mitigation effects of lessening the production scale of electricity-generation sector will be weakened if production scale of leasing commercial services sector is also expanded. Simultaneous implementations may weaken the composite mitigation effects and come at the expense of system health.