Greenhouse gases prevent the cooling of the Earth’s surface. There are six main such gases, including carbon dioxide, methane, chlorofluorocarbons, and nitrous oxides. Normally, as the Earth’s surface is warmed by sunlight, heat from infrared rays is radiated into space, thereby avoiding overwarming. However, if concentrations of greenhouse gases increase, infrared rays are absorbed, and heat is trapped. Although methane and chlorofluorocarbons have stronger greenhouse effects than CO2, countries have been targeting mainly CO2 because of its much greater emission volume.