How Emissions Trading Works
Emissions trading systems (ETS), also known as cap-and-trade, take a fundamentally different approach from carbon taxes. Instead of setting a price and letting the market determine emissions, an ETS sets a quantity limit and lets the market determine the price. This lesson explains the core mechanics.
The Basic Concept
An ETS works in three steps:
Step 1: Set a cap
The government sets an overall limit (cap) on total emissions from covered sources. For example, "the power sector can emit no more than 100 million tons of CO2 this year."
Step 2: Create and distribute allowances
The government creates tradable permits called allowances, each representing the right to emit one ton of CO2. The total number of allowances equals the cap. These are distributed to covered entities through free allocation, auction, or a combination.
Step 3: Require surrender and allow trading
At the end of each compliance period, entities must surrender allowances equal to their actual emissions. If an entity emits less than its allowances, it can sell the surplus. If it emits more, it must buy additional allowances.
Think of an ETS like a fishing quota system. The government decides how many fish can be caught (the cap). Fishing boats receive or buy permits for specific quantities. Boats that catch fewer fish than their quota can sell permits to boats that need more. Total catch cannot exceed the cap, but individual boats have flexibility.
Why Trading Makes the System Efficient
Trading is the magic of cap-and-trade. It ensures emissions reductions happen wherever they are cheapest.
Example:
Two power plants, each emitting 100,000 tons and holding 80,000 allowances. Both must cut 20,000 tons to comply.
- Plant A can reduce emissions cheaply by switching from coal to gas at $30/ton
- Plant B would need expensive equipment upgrades at $70/ton
Without trading, each plant spends what it costs to reduce 20,000 tons:
- Plant A: $30 × 20,000 = $600,000
- Plant B: $70 × 20,000 = $1,400,000
- Total: $2,000,000
With trading, Plant A reduces more and sells allowances:
- Plant A reduces 40,000 tons at $30/ton = $1,200,000
- Plant A sells 20,000 allowances to Plant B at $50/ton = $1,000,000
- Plant A's net cost: $200,000
- Plant B buys allowances: $1,000,000
- Total: $1,200,000
Same emissions reductions, $800,000 less cost. Both plants are better off, and the environment gets the same outcome.
Trading does not weaken environmental outcomes. Total emissions are still capped at the same level. Trading just ensures that reductions happen at the lowest cost. This is what economists mean by efficiency.
Key Components of an ETS
The cap
The legal limit on total emissions. Usually declines over time to drive emissions reductions. Expressed in tons of CO2 equivalent per compliance period (typically one year).
Allowances
Tradable permits, each authorizing one ton of emissions. Created by government, tracked in electronic registries, surrendered for compliance.
Covered entities
The businesses required to participate. Usually large point sources: power plants, industrial facilities, sometimes aviation. Defined by sector and size thresholds.
Compliance period
The time frame over which emissions are measured and allowances surrendered. Usually one calendar year.
Monitoring, reporting, and verification (MRV)
Systems to accurately measure and report emissions. Third-party verification ensures data quality.
Registry
Electronic database tracking allowance ownership, transfers, and surrender. Essential for market integrity.
Trading infrastructure
Markets (formal exchanges or over-the-counter) where allowances are bought and sold. Regulators oversee to prevent manipulation.
The Compliance Cycle
An ETS operates in an annual cycle:
January-December: Covered entities operate and emit CO2. They monitor emissions throughout the year.
January-March (following year): Entities prepare and submit verified emissions reports for the previous year.
April-May: Entities surrender allowances equal to their verified emissions.
Ongoing: Trading occurs throughout the year as entities buy or sell based on their expected needs.
| Month | Activity |
|---|---|
| Year 1 | Operations and emissions |
| Jan-Feb Year 2 | Prepare emissions report |
| March Year 2 | Independent verification |
| April Year 2 | Report submission |
| May Year 2 | Allowance surrender deadline |
| Continuous | Trading and market activity |
How Prices Are Determined
In an ETS, prices emerge from supply and demand:
Supply: Fixed by the cap (number of allowances in circulation)
Demand: Determined by emissions levels and expectations
Price equilibrium: Where supply equals demand
ETS prices respond to many factors:
Factors that raise prices:
- Economic growth (more industrial activity, more emissions)
- Cold winters (more heating demand)
- Low renewable energy output (more fossil generation)
- Tightening of future caps
- Increased auction frequencies
- Policy signals toward higher ambition
Factors that lower prices:
- Economic recession (less industrial activity)
- High renewable energy output
- Mild weather
- Oversupply of allowances
- Banking of surplus allowances from previous periods
- Political uncertainty about the system's future
The EU ETS experience: EU ETS prices collapsed during the 2008 financial crisis (from €30 to under €10) as recession reduced demand. Prices remained low for years until reforms tightened supply. By 2023, prices exceeded €80 as the market tightened.
This volatility is a feature, not a bug. Prices respond to changing conditions. But extreme volatility can undermine investment signals, which is why many systems now include price stability mechanisms.
Comparing ETS to Carbon Tax
| Feature | ETS (cap-and-trade) | Carbon tax |
|---|---|---|
| What government sets | Quantity (cap) | Price (rate) |
| What market determines | Price | Quantity |
| Certainty | Emissions quantity certain | Price certain |
| Uncertainty | Price can fluctuate | Emissions may vary |
| Complexity | Higher (market infrastructure) | Lower |
| Revenue timing | Auctions (may be periodic) | Continuous |
Why Choose an ETS?
Emissions trading offers several advantages:
Quantity certainty
The cap guarantees that covered emissions will not exceed a specific level. This matters for meeting climate targets.
Dynamic efficiency
Prices adjust automatically to economic conditions. In a recession, the price falls, reducing compliance costs. In growth periods, the price rises to constrain emissions.
Potential for linking
Different ETS systems can link together, allowing cross-border trading. This expands the market and can reduce overall costs.
Compatibility with offsets
An ETS can allow credits from outside the covered sectors (like forest projects) to be used for compliance, potentially reducing costs further.
Why an ETS Might Not Be Right
Emissions trading also has disadvantages:
Price volatility
Without price stability mechanisms, ETS prices can swing dramatically, undermining investment planning.
Complexity
Running an ETS requires market infrastructure, registries, sophisticated MRV, and market oversight. This is more complex than a carbon tax.
Risk of oversupply
If the cap is set too loosely or economic conditions reduce emissions below expectations, allowance surplus can collapse prices.
Market manipulation risks
Trading markets can be vulnerable to manipulation without proper oversight.
Real-World Scale
Emissions trading has grown dramatically:
| System | Launch year | Coverage | 2024 price |
|---|---|---|---|
| EU ETS | 2005 | ~40% of EU emissions | ~€80 |
| China national ETS | 2021 | Power sector (~40% of emissions) | |
| California | 2012 | ~80% of state emissions | ~$35 |
| RGGI (US Northeast) | 2009 | Power sector | ~$15 |
| South Korea | 2015 | ~70% of emissions | ~$15 |
| UK ETS | 2021 | ~30% of emissions | ~£50 |
The EU ETS is the world's oldest and largest carbon market. China's ETS, while newer, covers more absolute emissions than any other system because of China's scale. Together, these two systems cover about 25% of global emissions.
Looking Ahead
In the coming lessons, we will dive deeper into ETS design: how to define scope and coverage, how to set the cap, how to allocate allowances, and how to manage price volatility. Each design choice has important implications for environmental effectiveness, economic efficiency, and political sustainability.