Greenhouse gases are several chemical species present in the atmosphere which have the property of trapping much of the solar radiation reflected from the Earth . When irradiated by incoming solar radiation,  the atmosphere permits entry of most of the impinging energy of the solar electromagnetic spectrum; however, the spectrum of reflected sunlight is altered and has a higher fraction of long wave radiation, which is preferentially absorbed by greenhouse gases. Thus the net effect of higher concentrations of greenhouse gases is to encourage net heat buildup of the Earth’s atmosphere. Through normal heat exchange processes between the atmosphere and Earth’s surface, the temperature at the Earth’s surface is correspondingly elevated.

The steady increase in atmospheric concentrations of the three main greenhouse gases to which humans make notable contributions – carbon dioxide, methane, and nitrous oxide– is clear from the data sets for these gases over the last 420,000 years. Since the Industrial Revolution, concentrations of carbon dioxide, methane, and nitrous oxide have all risen sharply. Intensification of agriculture, fossil fuel combustion, land cover alteration to peatlands and wetlands have been the primary causes for these changes; however, all of these drivers are underlain by a root cause of the expanding global human population.

The analysis of greenhouse gas impacts on climate is the object of intense study, but is extremely complex due to the interactions of ocean currents and the diversity of carbon dioxide and methane sinks, which include forests, surface waters, peatlands and tundra. The situation is also complex since methane levels are rising faster percentagewise than carbon dioxide, and methane has approximately 30 times the greenhouse potency of carbon dioxide. The issue would be relatively simple, if all greenhouse gas emissions were merely the result of combustion processes, but production of methane is preponderantly from livestock grazing, rice farming and other non-point sources that are often linked to livelihoods of people in developing countries.