What's the difference between a Certified Emission Reduction (CER) and an EU Emission Allowance (EUA)?

EUAs are electronic certificates distributed to industry by European governments. Each represents the right to release one tonne of carbon dioxide into the atmosphere. There are a fixed number of EUAs. Carbon Retirement buys EUAs.

CERs are awarded by the United Nations to projects in the developing world that reduce emissions. Companies in the EU Emission Trading Scheme are allowed to offset a small proportion of their emissions using CERs.