What Is Carbon Tax?

A carbon tax is a fiscal instrument that places a direct price on greenhouse gas emissions by requiring emitters to pay a fee proportional to the quantity of CO2 or CO2-equivalent gases they release. By raising the cost of carbon-intensive activities, the tax creates a financial incentive for firms and households to reduce fossil fuel consumption, invest in energy efficiency, and shift toward lower-carbon alternatives. The tax is expressed in currency per tonne of CO2 emitted and can be applied at the point of fuel extraction, import, sale, or combustion.

Carbon taxation is one of two principal categories of market-based climate policy instruments; the other is emissions trading, in which a cap on total emissions is set and covered entities buy and sell allowances. Where a carbon tax provides certainty about the price of carbon but leaves the resulting quantity of emission reductions uncertain, an emissions trading scheme fixes the quantity and lets the price fluctuate. The choice between these instruments, and hybrid combinations of them, is a central question in climate economics and policy design.

Mechanism and Economic Rationale

The economic justification for a carbon tax rests on the concept of an externality: carbon emissions impose costs on third parties through climate change, but those costs are not reflected in market prices unless the government corrects the market failure. By setting a tax equal to the estimated social cost of carbon, policymakers aim to align private incentives with social welfare. Estimates of the social cost of carbon vary widely depending on discount rate assumptions and the extent to which non-market damages are included, a point examined at length in the OECD's Pricing Greenhouse Gas Emissions 2024 report.

Tax revenues can be allocated in several ways: returned to citizens as dividends, used to reduce other taxes (a revenue-neutral design), directed to low-carbon investment programs, or deposited into general government funds. The distributional effects of a carbon tax tend to be regressive in isolation, since lower-income households spend a larger share of income on energy, so revenue recycling designs frequently include compensatory transfers.

Global Coverage and Implementation

The OECD's Effective Carbon Rates 2023 report found that roughly 27 percent of global greenhouse gas emissions were subject to a carbon tax or covered by an emissions trading scheme as of that year, up from 15 percent in 2018. Carbon taxes have been implemented at national and subnational levels across several dozen jurisdictions. Sweden introduced its carbon tax in 1991 at a level that has since risen to among the highest in the world; British Columbia's revenue-neutral carbon tax, implemented in 2008, became an influential model for subsequent designs. As analyzed by the OECD's Tax Policy and Climate Change report for the G20, the policy instrument works best when combined with complementary regulatory measures and clear long-term price trajectories that support investment planning.

Relationship to Carbon Dioxide Emissions

A carbon tax is typically structured around carbon dioxide as the primary reference gas, with other greenhouse gases converted to CO2-equivalent using global warming potentials established by the Intergovernmental Panel on Climate Change (IPCC). Fossil fuel combustion remains the dominant source of CO2 emissions targeted by carbon pricing, with industrial processes, agriculture, and land-use change covered to varying degrees depending on national implementation choices.

Applications

Carbon tax has applications in a wide range of policy and engineering contexts, including:

• National and subnational climate policy frameworks
• Energy system planning and decarbonization investment analysis
• Corporate emissions accounting and climate risk disclosure
• Fuel pricing and transportation infrastructure policy
• International trade policy, including border carbon adjustments