Overview
Cap-and-trade is a policy mechanism built on two ideas working together. First, set a hard limit, the cap, on the total amount of greenhouse gases that a defined set of emitters can release in a given period. Second, let companies trade the permits (called allowances) that authorise those emissions. Companies that cut their emissions faster than required end up with spare allowances they can sell; companies that overshoot their allocation must buy more. The cap declines over time, making allowances progressively scarcer and more expensive.
The elegance of the system is that it combines environmental certainty (the cap guarantees a maximum level of emissions) with economic efficiency (emission reductions happen wherever they’re cheapest, not necessarily where the regulator dictates). A steel mill might find it far cheaper to buy allowances than to retrofit its furnaces; a power utility might find the opposite. The market sorts it out.
Cap-and-trade is a compliance instrument, it operates through regulation, not voluntary action. This distinguishes it sharply from the voluntary carbon market, where companies purchase Carbon Offsets as a discretionary act. Allowances granted under a cap-and-trade system are legal rights to emit; offsets are certificates from separate projects. Conflating them is a persistent source of confusion in climate communications.
The system sits within the broader architecture of the Paris Agreement, which allows countries to use carbon markets in meeting their nationally determined contributions, the subject of ongoing negotiations under Article 6.
The EU Emissions Trading System
The EU Emissions Trading System (EU ETS), launched in 2005, is the world’s largest and most mature cap-and-trade programme. It covers around 40% of EU greenhouse gas emissions, including power generation, heavy industry, aviation within the European Economic Area, and, since 2024, maritime shipping.
The EU ETS has gone through significant reform since its early years, when a surplus of allowances kept the carbon price too low to drive meaningful investment in clean technology. Phase IV (2021-2030) introduced a faster cap reduction rate and the Market Stability Reserve, a mechanism that withdraws surplus allowances from circulation to maintain price signals. By 2023, EU allowance prices had reached highs above EUR 90 per tonne, a level that began to make fuel switching and clean technology investment genuinely competitive.
The EU ETS is closely linked to the EU Taxonomy and the EU Green Deal, which set the broader decarbonisation policy framework within which the ETS operates.
Other Major Systems
California-Quebec: The Western Climate Initiative links California’s cap-and-trade programme with Quebec’s, creating a cross-border carbon market. It covers about 85% of California’s economy-wide emissions and is one of the most comprehensive subnational systems in the world.
RGGI (Regional Greenhouse Gas Initiative): A cooperative of northeastern US states covering power sector emissions only. It’s more limited in scope than California’s system but has been operating since 2009 and has generated significant revenue reinvested in energy efficiency and clean energy programmes.
China: China launched its national ETS in 2021, covering the power sector. By volume of covered emissions, it’s the largest cap-and-trade system in the world, though its carbon price has been much lower than the EU’s and its rigour has been questioned by outside analysts.
Scarcity Is the Point
The cap creates scarcity. Scarcity creates a price signal. The price signal changes investment decisions. That chain of causality is the entire logic of the system, and it only works if the cap is genuinely tight. A cap set too generously, with too many free allowances distributed to industry, produces a low carbon price that fails to incentivise change. This was the central failure of the EU ETS in its early phases.
For communications professionals, the carbon price is a number worth tracking. A high, stable, and rising carbon price is evidence that the system is working. It also has direct implications for corporate costs, asset valuations, and the financial risk of high-carbon business models, the kind of Transition Risks that the TCFD framework asks companies to disclose.
The Stranded Assets concept is closely linked to carbon pricing: as the carbon price rises, assets that depend on cheap carbon start to lose their economic value, potentially before the end of their intended life.