CER - Certified Emission Reduction: These emissions reduction are generated by projects registered with UNFCCC. A certified emission reduction or CER is a unit issued pursuant to Article 12 and requirements there under, as well as the relevant provisions in the CDM modalities and procedures, and is equal to one metric tonne of carbon dioxide equivalent, calculated using global warming potentials defined by decision 2/CP.3 or as subsequently revised in accordance with Article 5 of the Kyoto Protocol.

VER - Voluntary Emission Reduction. The emission reductions which could not be a part of CDM project activities due to technical or some other constraints.

1 CER or 1 VER refers to reduction in 1 tonne of CO2, that would have been emitted in normal scenario i.e. baseline for the project activity.

The crediting period for a CDM project activity is the period for which reductions from the baseline are verified and certified by a designated operational entity for the purpose of issuance of certified emission reductions (CERs). Project participants shall choose the starting date of a crediting period to be after the date the first emission reductions are generated by the CDM project activity. A crediting period shall not
extend beyond the operational lifetime of the project activity.

The crediting period may only start after the date of registration of the proposed activity as a CDM project activity. In exceptional cases, for project activities starting between 1 January 2000 and the date of the registration of a first clean development mechanism project, the starting date of the crediting period may be prior to the date of registration of the project activity if the project activity is submitted for registration before 31 December 2005 (please refer to paragraphs 12 and 13 of decision 17/CP.7, paragraph 1 (c) of decision 18/CP.9 and clarifications by the Executive Board, available on the UNFCCC CDM website).

The project participants may choose between two options for the length of a crediting period: (i) fixed crediting period or (ii) renewable crediting period, as defined in paragraph 49 (a) and (b) of the CDM M & P.

Upon issuance of CERs, the CDM registry administrator shall, in accordance with paragraph 66 of CDM modalities and procedures, promptly forward the CERs to the registry accounts of project participants involved, in accordance with their request, having deducted the quantity of CERs corresponding to the share of proceeds to cover administrative expenses for the Executive Board and to assist in meeting costs of adaptation for developing countries vulnerable to adverse impacts of climate change, respectively, in accordance with Article 12, paragraph 8, to the appropriate accounts in the CDM registry for the management of the share of proceeds.