Evaluating nature-based solutions for climate mitigation and conservation requires comprehensive carbon accounting

Keith et al. 2021

Whilst the science is clear that nature-based solutions have high potential for contributing to climate change mitigation, there remains uncertainty and confusion as to how to estimate this potential for a given project. This paper highlights that carbon accounting has often missed important aspects of the carbon cycle, and has predominantly focused on flows of carbon rather than stocks, which has in some cases led to undervaluation of intact ecosystems as carbon stores. The authors outline ten key components that are often excluded from current carbon accounting:

1. Include the spatial area of each land cover type in accounts, clearly categorized by degree of management (e.g. production or conservation forest).
2. Record all carbon pools, even if estimated; for example, belowground tree biomass comprises about 20% of total tree biomass but is often excluded.
3. Record the quality of carbon stocks, including the risk of carbon loss. For example, natural, production and plantation forests have different risks of carbon loss.
4. Account for changes in forest cover, to avoid missing change in carbon stocks such as logged areas.
5. Include the biosphere and atmosphere as separate units, otherwise some transfers to the atmosphere may be omitted.
6. Use the natural state of the ecosystem as the reference level, rather than change since business-as-usual or mature forest.
7. Measure gross flows, including removals due to growth, emissions due to fire and emissions due to logging, rather than focusing on net flows. This shows absolute gains and losses in carbon and reveals differences caused by forest management.
8. Use the long-term average carbon stock, rather than annual biomass increments that overlook the longevity of the carbon stock.
9. Treat carbon storage as an ecosystem service, separate from carbon sequestration; failure to do so can hide the risk of mass release of carbon from ecosystem degradation and conversion.
10. Account for the opportunity cost in the absence of human intervention, so carbon sequestration potential is the difference between the current carbon stock and the carbon carrying capacity.

Read the paper here.