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What is additionality? Examples and problems

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By illuminem

· 4 min read

This article is part of illuminem's Carbon Academy, the ultimate free and comprehensive guide on key carbon concepts 

1. Definition

In the realm of carbon markets, additionality is a pivotal concept, serving as a test for the credibility and impact of carbon offset projects. These markets, designed to facilitate greenhouse gas emissions reduction, demand additionality to ensure the legitimacy of a claimed emission reduction.

Emission reductions claimed by offset projects achieved must be “additional” to what would have happened without the project, in the sense that they have to demonstrate that they are providing a genuine surplus of emission reductions. If not, the carbon offset project is to be considered worthless. In other words, the project only brings additional benefit for climate if the project would not have happened without the money the individual pays for that offset (i.e. it happens only thanks to the fact that those projects were capable of joining carbon markets).

2. Examples

Let us show the concept of additionality in action through a double example of an additional and non-additional project

a) Additional Project
A reforestation initiative in a region where deforestation is prevalent. The project involves planting native trees and implementing sustainable forest management practices. The area selected for reforestation has a history of logging activities, and without the carbon offset funding, the economic pressures would likely lead to continued deforestation. The funds from carbon credits make it economically viable to conserve and restore the forest, resulting in a net reduction in carbon emissions.

b) Non-Additional Project
Installing solar panels on a building in a city where government regulations and incentives already make solar energy projects economically feasible. In this case, the project might have proceeded even without the carbon offset funding because the local policies and economic conditions were already favorable for renewable energy adoption. The carbon credits, in this scenario, may not have been the deciding factor for the project's implementation, making it non-additional.

3. Problems

Additionality is not easy to determine and verify, requiring precise definition of how many emissions would be emitted without the implementation of the project. Put differently, the main challenge lies in the difficulty of accounting the offsetting activity in a counterfactual reality that cannot be observed directly.

Additionality is primarily determined based on the following criteria:

  • Investment Analysis: This method assesses whether the project requires external financial support to be viable. If the project is financially feasible without carbon finance, it may not be considered additional
  • Additionality Baselines: Establishing a baseline scenario against which the project's emissions reductions are compared. If the project's emissions are lower than the baseline, it is considered additional
  • Dynamic Baseline: Considers the evolving nature of business-as-usual scenarios, accounting for changes over time and ensuring that the baseline reflects the most realistic future without the project
  • Leakage Assessment: Leakage refers to the potential increase in emissions outside the project boundary due to the project's activities. Assessing and mitigating leakage is crucial for ensuring additionality
  • Common Practice Test: Compares the project's emissions intensity to the emissions intensity of similar projects or activities in the region. If the project is less carbon-intensive than common practice, it may be considered additional
  • Financial Additionality: Examines whether the project's financial returns depend on the revenue generated from the sale of carbon credits. If carbon finance is a significant driver for the project, it may be considered additional
  • Technology Demonstration: Assesses whether the project involves the demonstration of a new and innovative technology that goes beyond what is currently common practice. Projects introducing new, less carbon-intensive technologies may be considered additional
  • Sustainable Development Additionality: Evaluates whether the project contributes to sustainable development beyond emissions reductions. This could include social, economic, and environmental co-benefits, ensuring a holistic view of additionality.


In summary, additionality is one of the main parameters in carbon markets ensuring that investments lead to tangible environmental benefits, aligning the market with the overarching objective of mitigating climate change through credible emission reduction initiatives.

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