There were two definite elements of the cap and trade scheme: the cap itself, and the ability to trade (Department of Climate Change, 2008, 12). The cap is the limit on greenhouse gas emissions imposed by the Carbon Pollution Reduction Scheme. The system aims at achieving the environmental outcome of reducing greenhouse gas emissions, the idea being that capping emissions creates a price for carbon and the ability to trade ensures that emissions are reduced at the lowest possible price (Department of Climate Change, 2008, 12). Setting a limit means that the right to emit greenhouse gases becomes scarce, and scarcity entails a price. The Carbon Pollution Reduction Scheme would have put a price on carbon in a systematic way throughout the economy (Department of Climate Change, 2008, 13).