The United Nations Framework Convention on Climate Change was signed in 1992 in Rio de Janeiro, Brazil. The Convention's goal is to minimize the anticipated damage to global climatic systems. In order to turn the Convention into an effective environmental and economical means, an addendum to the Convention was adopted in 1997, known as the Kyoto Protocol, which entered into force in 2005. Within the framework of the Protocol, as part of the global effort to fight global warming, mechanisms were determined for the trade of certified greenhouse gas emission reduction credits. These mechanisms provide well defined methods of measuring Co₂ and other GHG reductions (see below). These GHG reductions are then available for trade. This market is among the fastest growing markets worldwide.

The following is a list of greenhouse gasses that are covered by the Kyoto Protocol and their equivalent Co₂ value.