Natural greenhouse gas sources are those that generate any of the five principal gases, are continuously being recycled through the atmosphere, and have been present for millions of years. Among many natural GHG sources, the most popular are photosynthesis, respiration, and volcanoism [8].
On the other hand, anthropogenic GHG sources arise mainly from producing energy. Below is the breakdown of U.S anthropogenic greenhouse gas emissions by gas as of 2001.
It is shown that as of 2001, 82 percent of human-made GHG emissions can be attributed to the burning of fossil fuels for energy. Other notable GHG sources that are human-induced are landfills, coal mines, oil and gas operations, agriculture, industrial processes, and some fertilizers[9].
