Additionality 

A principle used in carbon accounting to evaluate carbon reduction or removal projects and a key criterion for carbon offset projects in voluntary and compliance carbon markets. The additionality principle helps to ensure that carbon credits or climate finance support projects that genuinely contribute to mitigating climate change, rather than rewarding actions that would have occurred regardless. 

For example, if a renewable energy project is funded using carbon credits, yet would still have been undertaken (through private financing) in the absence of carbon financing, then it would not meet the criteria of additionality. This may be the case if a country has strong mandates or subsidies for renewable energy projects.