Additionality is a defining concept of carbon-offset projects. To qualify as a genuine carbon offset, the reductions achieved by a project need to be ‘additional’ to what would have happened if the project had not been carried out (e.g. continued as business-as-usual). For instance, if a project is viable in its own right, say through the sale of electricity, or because of government funding, regulation or other policies, then it cannot be used as an offset project as it would have been undertaken regardless of investment secured through carbon markets. 

The concept of additionality is important as only carbon credits from projects that are “additional to” the business-as-usual scenario represent a net environmental benefit. Without the “additionality” requirement, there is no guarantee that the emissions reduction activities will lead to a reduction of greenhouse gases into the atmosphere. Therefore, in simple terms, if carbon credits are awarded to activities that would have happened anyway, emissions are allowed to rise without a corresponding cut elsewhere, therefore making the process meaningless. Any business or individual considering purchasing carbon credits to ask questions to ensure that the standard or system backing the credits require proof of additionality.