Additionality is a term used by Kyoto’s project-based mechanisms (i.e. Clean Development Mechanism and Joint Implementatin projects) to describe the fact that a carbon dioxide reduction project (carbon project) would not have occurred had it not been for concern for the mitigation of climate change. More succinctly, a project that has proven additionality is a beyond business as usual project.
It is generally agreed that voluntary carbon offset projects must also prove additionality in order to ensure the legitimacy of the environmental stewardship claims resulting from the retirement of the carbon credit (offset). According the World Resources Institute/World Business Council for Sustainable Development (WRI/WBCSD):
“GHG emission trading programs operate by capping the emissions of a fixed number of individual facilities or sources. Under these programs, tradable ‘offset credits’ are issued for project-based GHG reductions that occur at sources not covered by the program. Each offset credit allows facilities whose emissions are capped to emit more, in direct proportion to the GHG reductions represented by the credit. The idea is to achieve a zero net increase in GHG emissions, because each tonne of increased emissions is ‘offset’ by project-based GHG reductions. The difficulty is that many projects that reduce GHG emissions (relative to historical levels) would happen regardless of the existence of a GHG program and without any concern for climate change mitigation. If a project ‘would have happened anyway,’ then issuing offset credits for its GHG reductions will actually allow a positive net increase in GHG emissions, undermining the emissions target of the GHG program. Additionality is thus critical to the success and integrity of GHG programs that recognize project-based GHG reductions.”