California is concerned that entities that emit greenhouse gases (GHG) have accrued a too-large bank of allowances through the Air Resources Board (CARB) cap-and-trade program (CATP.) The excess is estimated at 321 million allowances (one allowance equals one metric tonne of carbon dioxide equivalent (CO2e) emissions). This is more an a year’s worth of allowances. About half of these were issued for free to eligible energy utilities and energy-intensive trade-exposed (EITE) companies.

The state could consider purchasing back a certain portion to reduce the backlog and increase the market price so as to further encourage reductions in GHG emissions by retiring those allowances. Prices in the last allowance auction ranged from $28 to $34 per allowance/tonne. If California bought back half or 160 million allowances at those prices, it would cost $4.5 to $5.5 billion. That would create effectively a reduction of 160 million tonnes in future GHG emissions.

That should be compared to the various benchmarks for the benefits and costs of reducing GHG emissions. The currently accepted social cost of GHG emissions developed by the U.S. Environmental Protection Agency (US EPA) is ranges from $50 to $150 per tonne in 2030 (and recent studies have estimated that this is too low.) That would create a net social benefit from $2.5 to $19.6 billion.

CARB’s AB 32 Scoping Plan update estimates the average cost of reductions without the CATP to be $70 per tonne in 2030. The incremental avoided costs of the CATP are estimated at $220 per tonne. The net avoided costs on this basis would range from $5.7 to $30.4 billion.