In addition to the most important man-made greenhouse gas, carbon dioxide (CO₂), there are other greenhouse gases such as methane or nitrous oxide. The various gases do not contribute to the greenhouse effect to the same extent and remain in the atmosphere for different periods of time.
In order to make the effects of different greenhouse gases comparable, the Intergovernmental Panel on Climate Change (IPCC) of the United Nations has defined the so-called "Global Warming Potential". This index expresses the warming effect of a certain amount of a greenhouse gas over a set period of time (usually 100 years) in comparison to CO₂ . For example, methane’s effect on the climate is 28 times more severe than CO₂, but it doesn’t stay in the atmosphere as long. The environmental impact of nitrous oxide also exceeds that of CO₂ by almost 300 times. The anthropogenic source of these greenhouse gases can be found in agriculture through the use of nitrogen fertilizers and livestock farming. In this way, greenhouse gases can be calculated as CO₂ equivalents. CO₂ equivalents are abbreviated with "CO₂e".