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.

$2 Billion Raised for Clean Energy

Since launch in 2010, Carbon Lighthouse Association  and its donors have eliminated the emissions of 3 power plants. The best part is the money is recycled into the clean energy economy: all proceeds raised by the State auctions is used to fund energy efficiency and renewable energy research and deployment. Since 2006, more than 2 billion dollars have been raised for clean energy, while simultaneously raising the cost of polluting in the USA.