The Intergovernmental Panel on Climate Change (IPCC) proposes two hypothetical future scenarios. One is Scenario "A1B" based on the assumption that a future world will have more global economic growth (the concentration of carbon dioxide will be 720ppm in 2100). The other is Scenario "B1" based on the assumption that a future world will have global green economy (the concentration of carbon dioxide will be 550ppm in 2100).