In 10 US States (& Quebec!), every power plant is required by law to purchase one “allowance” for every ton of CO2 it emits. Any power plant caught operating without an allowance is fined heavily by the State government. The State governments needs revenue, so enforcement is strong.
These allowances are sold at an auction held each quarter by the State governments, and the total number of allowances available for purchase is fixed: any allowance purchased and not used to pollute results in one ton fewer of carbon emissions. Anyone who can navigate the legal paperwork and bid the minimum block is allowed to participate.
Each quarter, Carbon Lighthouse Association aggregates up consumer donations & uses them to out-compete power plants for pollution permits at these auctions. This permanently reduces the supply of allowances, and forces utilities to use cleaner sources of power like solar, wind, and natural gas instead of coal.