Greenhouse gases are released through natural processes (e.g. decomposition of biomass) and as a result of human activity (e.g. the burning of fossil fuels). Some gases are naturally occurring (e.g. carbon dioxide) while others are human-made (e.g. the halocarbons). Carbon dioxide (CO2) is the largest single contributor to climate change. The U.N. Framework Convention on Climate Change covers the following greenhouse gases: Carbon dioxide (CO2); Methane (CH4); Nitrous oxide (N2O); Fluorinated gases (F-gases).