As Congress considers legislation to reduce the greenhouse gas (GHG) emissions that contribute to climate change, attention has focused on cap-and-trade legislation. Such legislation would set a national cap on GHG emissions, with allowances (permits) to emit limited amounts of the gases distributed or auctioned to affected parties. Recently, there has also been discussion of taxes on greenhouse-gas-emitting substances (generally referred to as a carbon tax), which proponents argue would provide greater transparency and a clearer price signal.