Emissions trading is a market-based system for reducing pollution. Governments set a limit on how much total pollution a group of companies can release, then issue permits (called allowances) that give each company the right to emit a specific amount. Companies that pollute less than their limit can sell their unused permits to companies that need more. The result: pollution has a price, and there’s a financial incentive to cut it.
How Cap and Trade Works
The process starts with a cap, which is the total amount of emissions that all participating companies are allowed to produce during a set period. A government or regulatory body decides this cap based on an environmental target, then distributes allowances to companies. Each allowance typically equals one metric ton of carbon dioxide (or another pollutant like sulfur dioxide). Companies receive these allowances either for free or by purchasing them at auction.
Once a company holds allowances, it has three options: use them to cover its own emissions, sell them to another company on the open market, or bank them for future use. This flexibility is what makes the system work. A company that can cheaply upgrade its equipment and cut pollution will do so, then profit by selling the permits it no longer needs. A company facing expensive upgrades can buy those permits instead, staying in compliance while it plans longer-term changes.
At the end of each compliance period, every company must hold enough allowances to match its actual emissions. If it falls short, it faces automatic financial penalties and must make up the difference with future allowances. The cap itself typically shrinks over time, forcing the total amount of pollution down year after year. In the EU’s system, for instance, the cap decreases by 4.2% annually from 2026 through 2030.
Banking allowances for later use creates an interesting side effect: companies often reduce emissions faster than required in the early years of a program, generating extra reductions sooner than the schedule demands.
Two Main Approaches
Not all emissions trading systems work the same way. The two main designs are cap-and-trade and baseline-and-credit.
- Cap-and-trade sets an overall pollution ceiling for an entire sector or economy, then distributes allowances up to that ceiling. Companies trade those allowances among themselves. This is the more common approach globally.
- Baseline-and-credit works differently. Each company gets an individual emissions limit based on regulations. Credits are only generated when a company cuts its emissions below that specific limit, going beyond what the law requires. It can then sell those credits to companies struggling to meet their own limits. Colorado uses this model for greenhouse gases.
The key distinction: in cap-and-trade, allowances exist from the start and get traded. In baseline-and-credit, credits only come into existence when someone outperforms their legal obligation.
Where Emissions Trading Operates Today
Carbon pricing instruments, including emissions trading systems and carbon taxes, now cover roughly 28% of global greenhouse gas emissions. The largest and oldest major system is the EU Emissions Trading System (EU ETS), launched in 2005. It covers about 40% of the EU’s total greenhouse gas emissions across power generation, heavy industry (steel, cement, aluminum, oil refining, glass, and others), aviation within the European Economic Area, and, more recently, maritime shipping.
Other significant systems operate in California (linked with Quebec), China, South Korea, the United Kingdom, and New Zealand, among others. China’s national system, which began in 2021, covers the world’s largest volume of emissions but initially focused only on the power sector. Each system has its own rules for allocation, trading, and penalties, but the core logic is the same.
Has It Actually Reduced Emissions?
The EU ETS offers the longest track record. As of early 2025, emissions in the sectors it covers have fallen approximately 50% compared to 2005 levels. The system is on track to hit its target of a 62% reduction by 2030. That’s a substantial drop, though it coincided with other factors like the growth of renewable energy, efficiency standards, and economic shifts. Disentangling what the carbon market caused versus what it accompanied is difficult, but the price signal it creates clearly pushes investment decisions toward lower-emission options.
Research published in Scientific Reports found that carbon trading policies significantly promote green technology innovation, particularly among state-owned enterprises and companies with higher profitability. Companies respond to the cost of carbon by rethinking their supply chains and investing in cleaner processes. Interestingly, the innovation effect was weaker for smaller private firms and companies with thin profit margins, suggesting the policy works best for businesses with enough capital to invest in change.
Carbon Offsets and Their Limits
More than 60% of emissions trading systems worldwide allow companies to use carbon credits (offsets from projects like reforestation or methane capture) to meet some of their compliance obligations. But nearly all of them restrict how much. Depending on the system, offsets can cover anywhere from 3.3% to 100% of a company’s obligations, though most caps sit at the lower end.
Most systems also require that offset projects be domestic, meaning they must take place within the country or region where the trading system operates. South Korea is currently the only major system that still allows certain international credits, and even those face strict rules about project type and ownership. The EU ETS and New Zealand both used to accept international offsets but eliminated them in 2021 and 2015, respectively. These restrictions exist because verifying the quality of offset projects, especially those in other countries, has proven difficult, and regulators want to ensure that emissions reductions are real.
The Carbon Leakage Problem
One of the most persistent criticisms of emissions trading is carbon leakage: when companies relocate production to countries with weaker climate rules, simply moving the pollution elsewhere rather than eliminating it. If making steel in the EU becomes more expensive because of carbon costs, a steelmaker might shift operations to a country with no carbon price, potentially increasing global emissions rather than reducing them.
Governments address this in several ways. The EU gives free allowances to industries considered at high risk of leakage, reducing their compliance costs. Some EU member states also provide financial aid to energy-intensive industries facing higher electricity prices caused by the carbon market. The EU is additionally phasing in a Carbon Border Adjustment Mechanism, which essentially charges importers for the carbon embedded in goods like steel, cement, and aluminum, leveling the playing field so domestic producers aren’t undercut by competitors in countries without carbon pricing.
Why It Uses Markets Instead of Mandates
The core advantage of emissions trading over traditional regulation is efficiency. A straightforward regulation might require every power plant to cut emissions by 30%, regardless of cost. Emissions trading lets the market find the cheapest reductions first. A plant that can cut a ton of pollution for $10 will do so and sell its spare allowance to a plant that would spend $50 achieving the same reduction. The same environmental outcome costs less overall.
This also means the carbon price sends a consistent signal across the entire economy. Every investment decision, from building a new factory to choosing between fuel sources, incorporates the cost of emitting carbon. Over time, that price reshapes which technologies get funded, which products become competitive, and how quickly industries transition away from fossil fuels. The cap guarantees the environmental outcome; the market determines who pays and how the reductions happen.