Abstract
Nature-based climate solutions supply carbon credits generated from net carbon drawdown in exchange for project funding, but their credibility is challenged by the inherent variability and impermanence of drawdown. By evaluating drawdown benefits from a social cost of carbon perspective, project developers can enhance credibility and estimate impermanence by conservatively anticipating drawdowns to be eventually released following a release schedule, issuing additional credits when actual release is less severe than anticipated. We demonstrate how we can use ex post observations of drawdowns to construct optimal release schedules that limit the risk of failing to generate credits (non-delivery). We simulate both theoretical and real-life projects to examine how this approach balances the trade-off between generating credits evaluated as more permanent and limiting non-delivery risk. We discuss how this approach incentivises project performance and provides a pragmatic solution to challenges facing larger-scale implementation of nature-based climate solutions.
Supplementary materials
Title
Supplementary Information
Description
The SI is structured in five parts:
A: formal definition of how credits and their equivalent permanence are calculated under the PACT Framework.
B, C: detailed step-by-step illustrations and mathematical representations of how we obtained the optimal release schedules
D: analytical solutions of the credit cache volume, the key quantity for the construction of optimal release schedule, in the special cases when the carbon loss distributions can be expressed as simple parametric distributions.
E: additional results of Monte Carlo simulations of theoretical projects with different net carbon drawdown levels.
F: sensitivity analyses of several key free parameters in the model and a brief discussion of the results
G: detailed information on the method for quantifying annual carbon fluxes in real-life REDD+ projects
H: additional results of Monte Carlo simulations of multiple theoretical or real-life projects aggregated into a single project portfolio.
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