Externalities and the environment: positive and negative externalities in production and consumption, private and social costs and benefits, the welfare loss from market failure, and environmental market failure.

What this dot point is asking

Eduqas wants you to define positive and negative externalities in both production and consumption, distinguish private from social costs and benefits, show the resulting welfare loss on a diagram, and apply this to environmental market failure. Externalities are the most commonly examined cause of market failure and the basis for taxes, subsidies and tradable permits later in the module.

What an externality is

Externalities can arise in production (the act of producing a good affects others) or in consumption (the act of consuming it affects others). This gives four cases: negative production (factory pollution), positive production (a firm's research spilling over to rivals), negative consumption (smoking, drink-driving), and positive consumption (vaccination, education).

Private and social costs and benefits

Negative externalities and over-production

With a negative externality of production, the marginal social cost lies above the marginal private cost. The free market produces where supply (MPC) meets demand (MSB), but at that output the marginal social cost exceeds the marginal social benefit. Society would be better off producing less. The triangle between MSC and MSB over the over-produced units is the deadweight welfare loss: resources are over-allocated to a good whose social cost exceeds its social benefit.

Positive externalities and under-production

With a positive externality of consumption (for example education or vaccination), the marginal social benefit lies above the marginal private benefit. The free market consumes where private benefit meets private cost, but at that output the marginal social benefit exceeds the marginal social cost, so society would benefit from more consumption. The market under-provides the good, again creating a welfare loss. This is the efficiency case for subsidising merit goods.

Environmental market failure

The environment is the textbook large-scale externality. Pollution (air, water, noise), resource depletion and climate change are negative externalities of production and consumption: those who emit carbon do not bear the full cost of the warming it causes, which falls on others and on future generations. Because environmental resources are often non-excludable and treated as a free input, markets over-use them. This is why environmental policy relies on carbon taxes, tradable pollution permits and regulation to make polluters internalise the social cost.

Examples in context

• Vehicle emissions. Congestion and air pollution are negative externalities behind fuel duty, low-emission zones and the move to electric vehicles.
• Vaccination. A strong positive consumption externality (herd immunity), justifying free provision and subsidy.
• Carbon emissions. The defining global externality, addressed through carbon pricing and the EU and UK Emissions Trading Schemes.

Try this

Q1. Using a diagram, explain why a market with a negative externality of production over-allocates resources to the good. [4 marks]

• Cue. MSC lies above MPC; the market produces where MPC = MSB, but there $MSC > MSB$, so output exceeds the social optimum ($MSC = MSB$), giving a welfare loss.

Q2. Explain why education is regarded as generating positive externalities. [4 marks]

• Cue. Benefits beyond the individual (a more productive workforce, lower crime, higher tax revenue), so marginal social benefit exceeds marginal private benefit and the market under-provides.