Government Intervention to Correct Externalities | 纠正外部性的政府干预

📚 Government Intervention to Correct Externalities | 纠正外部性的政府干预

Externalities are costs or benefits imposed on third parties who are not directly involved in a market transaction. Because market prices only reflect private costs and private benefits, external effects can lead to allocative inefficiency. This article examines how governments use taxes, subsidies, regulations, tradable permits, property rights and information to correct externalities and bring private incentives closer to social outcomes.

外部性是指强加给未直接参与市场交易的第三方的成本或收益。由于市场价格只反映私人成本和私人收益，外部效应会导致配置无效率。本文考察政府如何运用税收、补贴、法规、可交易许可证、产权和信息等手段纠正外部性，使私人激励更接近社会最优结果。

1. Market Failure and Externalities | 市场失灵与外部性

Externalities are a major source of market failure: when third parties are affected by production or consumption, the free market price and quantity do not reflect the full social costs or benefits.

外部性是市场失灵的一个主要来源：当第三方受到生产或消费影响时，自由市场价格和数量没有反映全部社会成本或社会收益。

For a negative externality, the marginal social cost exceeds the marginal private cost, so the market produces too much. For a positive externality, the marginal social benefit exceeds the marginal private benefit, so the market produces too little.

对于负外部性，边际社会成本大于边际私人成本，因此市场产量过高；对于正外部性，边际社会收益大于边际私人收益，因此市场产量过低。

MSC = MPC + MEC and MSB = MPB + MEB

Here MEC is marginal external cost and MEB is marginal external benefit. These gaps justify government intervention to improve allocative efficiency.

这里 MEC 是边际外部成本，MEB 是边际外部收益。这些差额为政府干预以提高配置效率提供了依据。

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2. Negative Production Externalities | 负生产外部性

Negative production externalities arise when firms impose costs on others, such as air pollution from factories, water contamination or carbon emissions from power generation.

负生产外部性出现在企业给他人带来成本时，例如工厂空气污染、水污染或发电产生的碳排放。

The private supply curve reflects only the costs of the firm, so the market equilibrium occurs where MPB = MPC. Since MSC > MPC, the market quantity exceeds the socially optimal quantity, creating a deadweight welfare loss.

私人供给曲线只反映企业自身的成本，因此市场均衡发生在 MPB = MPC 处。由于 MSC > MPC，市场产量超过社会最优产量，造成无谓福利损失。

Governments can address this by shifting the private cost upward through a Pigouvian tax equal to the marginal external cost at the optimal output.

政府可以通过征收等于最优产量处边际外部成本的庇古税，使私人成本上移，从而解决这一问题。

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3. Negative Consumption Externalities | 负消费外部性

Negative consumption externalities occur when consumers impose costs on third parties. Examples include cigarette smoking, excessive alcohol use, private car congestion and plastic bag waste.

负消费外部性出现在消费者给第三方带来成本时。例子包括吸烟、过度饮酒、私家车拥堵和塑料袋垃圾。

The private benefit from consumption exceeds the social benefit because consumers ignore the harm to others. Therefore MPB > MSB, and the market over-consumes the good.

消费的私人收益大于社会收益，因为消费者忽视了对他人造成的损害。因此 MPB > MSB，市场会过度消费该商品。

A corrective tax on the product or an information campaign can reduce demand and bring consumption closer to the social optimum.

对该商品征收纠正性税收或开展信息宣传可以减少需求，使消费更接近社会最优水平。

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4. Positive Production Externalities | 正生产外部性

Positive production externalities occur when firms generate benefits for other producers or society. Research and development, worker training and disease-resistant crop innovation are common examples.

正生产外部性出现在企业为其他生产者或社会创造收益时。研发、员工培训和抗病作物创新是常见例子。

Because the innovating firm cannot capture all the benefits, MSB > MPB. The free market under-produces goods with positive production externalities, so there is an allocative inefficiency.

由于创新企业无法获得全部收益，MSB > MPB。自由市场对具有正生产外部性的商品生产不足，从而产生配置无效率。

Subsidies, patents or government-funded research can increase the private return and expand output toward the social optimum.

补贴、专利或政府资助的研究可以提高私人回报，使产量扩大到接近社会最优水平。

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5. Positive Consumption Externalities | 正消费外部性

Positive consumption externalities arise when individual consumption benefits others. Education reduces crime and raises productivity, vaccination reduces disease transmission, and public transport reduces congestion.

正消费外部性出现在个人消费使他人受益时。教育减少犯罪并提高生产率，疫苗接种减少疾病传播，公共交通减少拥堵。

Because consumers only consider their private benefit, MPB is below MSB. In a free market, too few people will choose these goods or services.

由于消费者只考虑私人收益，MPB 低于 MSB。在自由市场中，选择这些商品或服务的人会太少。

Governments can correct this by subsidising the activity, providing the good directly, or making consumption compulsory, as with primary education.

政府可以通过补贴该活动、直接提供商品或强制消费（如初等教育）来纠正这一问题。

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6. Indirect Taxes on Negative Externalities | 针对负外部性的间接税

A Pigouvian tax is an indirect tax set equal to the marginal external cost at the socially optimal output. It internalises the externality by making the polluter pay for the damage caused.

庇古税是一种间接税，税额设定为等于社会最优产量处的边际外部成本

Published by TutorHao | A-Level Economics Revision Series | aleveler.com

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