Environmental Problems and Externalities | 环境问题与外部性

📚 Environmental Problems and Externalities | 环境问题与外部性

Environmental problems such as air pollution, climate change and deforestation are classic examples of market failure. The fundamental reason is externality: producers and consumers impose costs or create benefits for third parties without these effects being reflected in market prices. This article explains the economics of externalities and examines policy solutions.

空气污染、气候变化与森林砍伐等环境问题是市场失灵的经典例子。其根本原因在于外部性：生产者和消费者对第三方造成成本或收益，而这些影响并未反映在市场价格中。本文将解释外部性的经济学原理并探讨政策解决方案。

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1. What Are Externalities? | 什么是外部性？

An externality is a cost or benefit arising from production or consumption that is experienced by a third party but is not included in the price paid by buyers or received by sellers. Externalities can be negative, such as pollution, or positive, such as education and vaccination.

外部性由生产或消费产生，由第三方承受，但并未包含在买方支付或卖方收到的价格中。外部性可以是负面的，如污染，也可以是正面的，如教育和疫苗接种。

Negative externalities occur when an activity harms people who are not directly involved in the transaction. A chemical plant that releases toxic waste into a river damages fishermen downstream and reduces public health. These social costs are ignored by the market equilibrium.

负外部性发生时，某项活动损害了未直接參與交易的第三方。例如，化工厂向河流排放有毒废物，损害了下游渔民并降低公众健康。这些社会成本被市场均衡所忽略。

Positive externalities occur when an activity benefits bystanders. For instance, an individual who installs solar panels reduces carbon emissions and improves air quality for everyone else, but the installer only receives a private benefit through lower electricity bills and feed-in tariffs.

正外部性发生时，某项活动使旁观者受益。例如，个人安装太阳能电池板能减少碳排放并改善所有人的空气质量，但安装者只通过降低电费和上网电价获得私人收益。

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2. Negative Externalities and Environmental Degradation | 负外部性与环境退化

When a firm produces goods, it only considers its own private costs such as raw materials, wages and rent. It does not consider the environmental costs imposed on society. The marginal private cost (MPC) is therefore lower than the marginal social cost (MSC).

企业生产商品时，只考虑自身的私人成本，如原材料、工资和租金，而不考虑强加给社会的环境成本。因此，边际私人成本 (MPC) 低于边际社会成本 (MSC)。

MSC = MPC + MEC

In the above equation, MEC is the marginal external cost, representing the damage caused by each additional unit of output, such as pollution, habitat loss and climate change. Because the producer ignores this external cost, the market supply curve reflects only MPC.

在上式中，MEC 是边际外部成本，代表每增加一单位产出造成的损害，如污染、栖息地丧失和气候变化。由于生产者忽略这一外部成本，市场供给曲线仅反映 MPC。

The profit-maximising firm produces where price equals MPC. However, the socially optimal output occurs where price equals MSC, which is lower. As a result, the free market produces too much of the polluting good, leading to excessive environmental degradation.

追求利润最大化的企业在价格等于 MPC 时生产，而社会最优产出发生在价格等于 MSC 时，后者水平更低。因此，自由市场会生产过多的污染产品，导致过度环境恶化。

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3. Positive Externalities and Environmental Benefits | 正外部性与环境效益

Many environmentally friendly activities generate positive externalities. Tree planting absorbs carbon dioxide, supports biodiversity and provides cooling shade. Those benefits are enjoyed by the wider community, not just by the landowner.

许多环保活动产生正外部性。植树吸收二氧化碳、支持生物多样性并提供清凉庇荫。这些收益由更广泛的社区享有，而不仅仅是土地所有者。

MSB = MPB + MEB

Here, MPB is the marginal private benefit, MEB is the marginal external benefit, and MSB is the marginal social benefit. Because the private individual does not capture the full social benefit, the market demand curve understates the true value of the environmental good.

其中 MPB 是边际私人收益，MEB 是边际外部收益，MSB 是边际社会收益。由于私人个体未获得全部社会收益，市场需求曲线低估了环境物品的真实价值。

The market equilibrium based on MPB is below the socially optimal level based on MSB. Consequently, green technologies, public parks and renewable energy are under-supplied, and society misses beneficial opportunities.

基于 MPB 的市场均衡低于基于 MSB 的社会最优水平。因此，绿色技术、公园和可再生能源供给不足，社会错失了有益的机会。

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4. Market Failure and Welfare Loss | 市场失灵与福利损失

Externalities cause market failure because prices do not signal the true social costs or benefits. In the presence of a negative externality, too much output is produced; in the presence of a positive externality, too little is produced. In both cases, resources are misallocated.

外部性导致市场失灵，因为价格无法传递真实的社会成本或收益。存在负外部性时产出过多，存在正外部性时产出过少。两种情况下资源都未被有效配置。

The overproduction of polluting goods creates a deadweight loss. The extra units produced beyond the socially optimal level generate private benefit, but the social cost of those units is even greater. The welfare loss is measured by the triangle between the MSC and MPC curves over the excess output.

污染商品的过度生产导致无谓损失。超过社会最优水平而额外生产的单位虽然产生私人收益，但社会成本更高。福利损失等于在超额产出区间内 MSC 曲线与 MPC 曲线之间的三角形面积。

Similarly, under-provision of positive externalities removes potential welfare gains. Using resources worth more than their cost, such as cleaner energy, would increase social welfare if the externality were internalised.

同样，正外部性供给不足会失去潜在的福利收益。如果外部性被内部化，那些价值大于成本的资源利用方式，如更清洁的能源，本可增加社会福利。

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5. Pigouvian Taxes: Internalising External Costs | 庇古税：内部化外部成本

A Pigouvian tax is a tax imposed on a polluting activity at a rate exactly equal to the marginal external cost. This technique internalises the externality by making producers bear the full social cost of their actions.

庇古税是对污染活动征收的一种税，税率恰好等于边际外部成本。这种政策通过让生产者承担其经济活动的全部社会成本来使外部性内部化。

Pigouvian tax = MEC

After the tax, the private marginal cost curve shifts upward, reflecting the external damage. The new market equilibrium occurs where price equals MSC, and output falls to the socially optimal level. Additional benefits include government revenue, which may compensate victims or fund environmental projects.

征税后，私人边际成本曲线上移，反映外部损害。新的市场均衡发生在价格等于 MSC 处，产出降至社会最优水平。此外政府还能获得财政收入，用于补偿受害者或资助环境项目。

However, applying a Pigouvian tax requires accurate measurement of external costs. Scientific uncertainty about climate damage or health effects makes it difficult to set the correct tax rate. Firms may also relocate to countries with looser regulations, creating carbon leakage.

然而，征收庇古税需要准确衡量外部成本。关于气候损害或健康影响的科学不确定性，使设定正确税率变得困难。企业也可能迁往监管更宽松的国家，造成碳泄漏。

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6. Subsidies: Encouraging Positive Externalities | 补贴：鼓励正外部性

To stimulate activities with positive externalities, governments may grant subsidies. A subsidy lowers the cost of production or consumption, shifting the supply curve downward and raising output from the private equilibrium toward the social optimum.Published by TutorHao | Economics Revision Series | aleveler.com

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