Additionality, baselines, and the proper accounting for land-based climate change mitigation efforts

Abstract

Carbon storage and uptake on land is a critical part of climate change mitigation. Each year, up to 30% of anthropogenic emissions are neutralized by the ongoing background land sink. At the same time, greenhouse gas emissions from deforestation and forest degradation are major contributors to climate change. Protecting the background sink, avoiding additional emissions, and increasing removals are all key parts of a climate change mitigation portfolio. However, accurately measuring the true mitigation effects of a given intervention is challenging because of an inherent reliance on a counterfactual—an estimate of what would have happened in the absence of a given intervention. These counterfactuals are handled differently in carbon markets and in national greenhouse gas inventories, which can lead to confusion in accounting for progress on climate change mitigation. In this paper, we review how global carbon budgets, national greenhouse gas inventories, and carbon markets account for land-based carbon fluxes. We also examine the implications for additionality and identify some particularly challenging cases. Finally, we present recommendations moving forward and connect this work to broader challenges relevant to other carbon dioxide removal pathways.