Economists have long favored a carbon tax as the most efficient policy to curb greenhouse gas emissions. One barrier to broader support for this policy option is its failure to ensure limits on emissions. Environmental groups, in particular, have expressed skepticism about carbon taxes for this failure to explicitly limit emissions. In response, policymakers have shown interest in a hybrid carbon tax that provides some assurance that emissions reduction targets will be met. To demonstrate how such a hybrid tax could work, I propose a prototype emissions assurance mechanism (EAM) that is practical, simple to implement, and easily understood. This EAM would be aimed at achieving a 45 percent reduction in energy-related carbon dioxide (CO2) emissions, relative to 2005 emissions, by 2035. This would put the United States on track for deep emissions reductions by mid-century. More specifically, the EAM would track actual emissions in each year relative to an emissions pathway. If cumulative emissions exceeded benchmarks along the pathway, then the tax rate would increase annually more rapidly at a rate established in the initial legislation. The emissions pathway is a policy choice that determines desired emission reductions; I suggest that the pathway and EAM be built into carbon tax legislation.

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排放保证机制：在美国碳税中增加环境确定性

长期以来，经济学家一直认为碳税是遏制温室气体排放的最有效政策。广泛支持该政策选择的一个障碍是无法确保排放限制。尤其是环保组织，对未能明确限制排放的碳税表示怀疑。作为回应，政策制定者对混合碳税表现出了兴趣，这种混合税可确保实现减排目标。为了演示这种混合税如何发挥作用，我提出了一个实用，易于实施且易于理解的原型排放保证机制（EAM）。该EAM的目标是到2035年将与能源有关的二氧化碳（CO2）排放量与2005年的排放量相比减少45％。这将使美国步入本世纪中叶之前实现大幅度减排的轨道。更具体地说，EAM将跟踪每年相对于排放途径的实际排放量。如果累计排放量超过该途径的基准，那么税率将以最初立法中确定的税率每年更快地增加。排放途径是决定所需减排量的政策选择；我建议将途径和EAM纳入碳税立法。排放途径是决定所需减排量的政策选择；我建议将途径和EAM纳入碳税立法。排放途径是决定所需减排量的政策选择；我建议将途径和EAM纳入碳税立法。