Nitrous Oxide (N2O) is the third most important GHG for the enhanced greenhouse effect after carbon dioxide (CO2) and methane (CH4). Although N2O makes up a relatively small amount of the atmosphere (about 330 parts per billion parts of atmosphere), it is with its GWP100yr about 270 and atmospheric lifetime of about 120 years very important for the global energy budget.
Nitrous oxide emissions are produced by both natural and human sources. The major natural sources include soils under natural vegetation, tundra and the oceans. Important human sources come from agriculture (nitrous oxide fertilizers, soil cultivation), livestock manure, biomass or fossil fuels combustion, and industrial processes. In total, over one third of the emissions are estimated to be due to human actions.
The nitrous oxide levels are now higher than at any other time during the last 800,000 years. Since the industrial revolution, the atmospheric concentrations of nitrous oxide have increased by 16%.