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 an emission-trading scheme (ETS) to reduce pollution.Graph and explain how an ETS works and why it is a good scheme to reduce pollution.