Projects can issue planned emission reductions (PERs - previously known as “validated certificates”) and verified emission reductions (VERs). PERs are “expected” emission reductions (ex-ante units) based on ex-ante estimations, whereas VERs are reductions that actually took place and have been verified (ex-post units).
Only VERs can be retired (removed from the market) for offsetting purposes. PERs can be issued on a 5-year cycle starting at Project Design Certification, and a new 5-year cycle can only be issued when all previously issued PERs are converted to VERs. Avoided greenhouse gas (GHG) emission projects cannot issue PERs. Avoided emissions are emission reductions that occur outside of a product's life cycle or value chain, but as a result of the use of that product.