The Intergovernmental Panel on Climate Change (IPCC) recent report state "It is unequivocal that human influence has warmed the atmosphere, ocean, and land. Widespread and rapid changes in the atmosphere, ocean, cryosphere, and biosphere have occurred". Many countries, even before this report, have introduced either a carbon tax or an emission-trading scheme (ETS) to reduce pollution. Graph and explain how the carbon tax and ETS differ.