In 2012, the state of California implemented a system of quantity regulation of greenhouse gases, which included tradable permits. This “cap-and-trade” program for greenhouse gas emissions distributes a fixed amount of greenhouse gas “allowances” to large emitters of greenhouse gases, such as electric power stations and large industrial plants. Plants may then purchase additional greenhouse gas emission allowances at auction, or, alternatively, may purchase unused allowances from another polluter. Theory predicts that this trading system will lead to a socially efficient allocation of pollution. Describe how such an outcome would occur.