The path to robust evaluation of carbon credits generated by forest restoration and REDD+ projects

Forest-focused Natural Climate Solutions (F-NCS) are crucial for climate change mitigation through emissions reductions and carbon sequestration. The Voluntary Carbon Market directs finance to F-NCS activities by the sale of carbon credits to offset emissions. However, inconsistent implementation and imprecise rules have led to over-crediting and other integrity challenges, reducing confidence in F-NCS effectiveness. Despite these concerns, assessments of the limitations of current protocols and how scientific advances could improve VCMs effectiveness have been piecemeal and limited in scope. To address this applied research gap, we review current and emerging methodologies for monitoring carbon impacts of forest protection and restoration activities, covering methods for monitoring carbon stock change, additionality, leakage, and non-durability, with an emphasis on integrating remote sensing (RS) technologies alongside field-based methods and emerging statistical approaches. We recommend 1) that the VCM needs to evolve as science advances. Carbon standards should also improve carbon estimates by 2) incorporating use of high-resolution maps of carbon stocks and change into standards; 3) establishing and sustainably financing a federated forest plots database for training and validation of carbon maps and testing new machine learning approaches; 4) calculate additionality for projects using causal inference methods that statisticians have developed for analysing changes in land cover and carbon density maps; 5) better understand the interaction between project and jurisdictional assessment of REDD+ projects; address leakage by 6) harnessing remote sensing to estimate its extent and evaluate the effectiveness of sustainable development measures designed to minimise it; 7) factor in non-durability upfront in F-NCS projects by leveraging map-based modelling of persistence. Implementation of these recommendations would improve accuracy and build confidence in the VCM, leading to real benefits for people, nature and the climate. • We review current and emerging methods for assessing REDD+ and ARR carbon impacts. • Remote sensing underpins all parts of assessment in REDD+ and ARR projects. • Statistically robust methods must be used to identify suitable project baselines. • Accurate carbon stock change assessment needs multi-sensor remote sensing methods. • We provide 7 recommendations to integrate research advances into VCM methods.