Parties with commitments under the Kyoto Protocol (Annex B Parties) have accepted targets for limiting or reducing emissions. These targets are expressed as levels of allowed emissions, or assigned amounts,at over the 2008-2012 commitment period. The allowed emissions are divided into assigned amount units (AAUs).
Emissions trading, as set out in Article 17 of the Kyoto Protocol, allows countries that have emission units to spare - emissions permitted them but not "used" - to sell this excess capacity to countries that are over their targets.
Thus, a new commodity was created in the form of emission reductions or removals. Since carbon dioxide is the principal greenhouse gas, people speak simply of trading in carbon. Carbon is now tracked and traded like any other commodity. This is known as the "carbon market".
The other units which may be transferred under the scheme, each equal to one tonne of CO₂, may be in the form of: A removal unit (RMU) on the basis of land use, land-use change and forestry (LULUCF) activities such as reforestation; An emission reduction unit (ERU) generated by a joint implementation project; A certified emission reduction (CER) generated from a clean development mechanism project activity.
根据《京都议定书》作出承诺的缔约方(附件 B 缔约方)已接受限制或减少排放的目标。这些目标以 2008 年至 2012 年承诺期内的允许排放水平或分配数量表示。允许的排放量分为分配数量单位(AAU)。
《京都议定书》第 17 条规定排放交易,允许国家将闲置排放单位(未使用的允许排放)出售给无法达到目标的国家。以减排或清除的形式创造了一种新商品,碳像任何其他商品一样被追踪和交易,这是所谓的“碳市场”。
碳市场的交易单位包括:去除单元(RMU):基于土地利用、土地利用变化和林业 (LULUCF) 重新造林等活动;减排单位(ERU):由联合执行项目产生;经认证的减排量 (CER):产生于清洁发展机制项目活动。