“双碳”背景下碳排放的边际外部性成本及最佳碳税的思考

The Marginal Externality Cost of Carbon Emissions and Considerations on the Optimal Carbon Tax in the Context of“Double Carbon”

气候变暖与环境恶化已成为人类生存和发展的重大威胁。鉴于碳排放具有负外部性,研究碳排放的边际外部性成本并探究最佳碳税,对于推进实现“双碳”目标具有重要意义。本文通过构建一个无限期的多部门新古典增长模型,探究碳排放的边际外部性成本及其影响因素,并对最优的碳税政策进行思考。研究结果表明:当居民消费效用函数呈对数形式、大气损害与产量成正比、大气中的碳含量存在线性关系和储蓄率不变等假设条件成立时,碳排放的边际外部性成本与产出成正比,且比例只与贴现率、大气损害函数和大气中的碳消散结构有关。因此,在碳税政策的制定上,要坚持经济发展与生态环境保护并重,分阶段动态优化调整碳税税率:在高贴现率时期提高碳税税率,分行业施行碳税政策和补贴政策,同时为了避免经济社会遭受到较大的冲击,起初征收碳税时税率不宜过高;考虑不同体量企业收入差距和负担能力,采用累进碳税征收机制;分地区实施差别税率,统筹区域协调发展。

Climate warming and environmental deterioration have become a major threat to human survival and development.Carbon emissions have negative externalities,so it is of great significance to study the marginal externality cost of carbon emissions and think about the optimal carbon tax for promoting the realization of the goal of“double carbon”.By constructing an infinite-horizon multisectoral neoclassical growth model,exploring the marginal externality cost of carbon emissions and its influencing factors,and reflecting on the optimal carbon tax policy,the results of the study show that when the assumptions of a logarithmic form of the utility function of the population’s consumption,a proportional relationship between atmospheric damage and output,a linear relationship between the carbon content in the atmosphere,and a constant savings rate are satisfied,the marginal externality cost of carbon emissions is proportional to output and the ratio is only related to the discount rate,the atmospheric damage function and the dissipation structure of carbon in the atmosphere.In the formulation of carbon tax policy,we should adhere to the equal importance of economic development and ecological environmental protection,adjust the carbon tax rate dynamically and optimally in phases,increase the carbon tax rate in the period of high discount rate,implement carbon tax policy and subsidy policy by industry,and at the same time,in order to avoid large shocks to the economy and society,the initial tax rate should not be too high;consider the income disparity and affordability of enterprises of different sizes,and adopt a progressive carbon tax levy mechanism.The tax rate should be different for each region,so as to coordinate regional development.