Green House Gases are gases in an atmosphere that absorb and emit radiation within the thermal infrared range. This process is the fundamental cause of the greenhouse effect. Common greenhouse gases in the Earth's atmosphere include water vapor, carbon dioxide, methane, nitrous oxide, ozone, and chlorofluorocarbons. Greenhouse gases, mainly water vapor, are essential to helping determine the temperature of the Earth; without them this planet would likely be much colder.

Human activity since the industrial revolution has increased the amount of greenhouse gases in the atmosphere, leading to increased radiative forcing from CO2, methane, tropospheric ozone, CFCs and nitrous oxide. The concentrations of CO2 and methane have increased by 36% and 148% respectively since the mid-1700s.

CO2 concentrations are continuing to rise due to burning of fossil fuels and land-use change. There is a sharp acceleration in CO2 emissions since 2000 to more than a 3% increase per year from 1.1% per year during the 1990s. The future rate of rise will depend on uncertain economic, sociological, technological, and natural developments.