California's cap-and-trade plan proposes to put a cap in greenhouse gas (GHG) emissions for some industries and create a market to trade the right to create pollution. Over time, the right to emit greenhouse gases is reduced, but emitters can use market forces through quarterly auctions to determine at what point it makes more sense to implement reductions and sell their emission rights, or invest in retrofitting systems and buying others' right to emit GHGs. The concern is that this plan will cause some companies to leave California to other states.