Refining Carbon Sequestration Models for Stronger, Investable Projects
By Bilal Hussain & Valeria Beljaeva
One of the challenges in carbon projects is ensuring sequestration models are not only scientifically sound but also credible and defensible for investors.
We recently worked with Medius Earth to assess their sequestration curve and validate key modelling assumptions for more than 40 species. Medius Earth are developing an afforestation regeneration project in Rajasthan, India on degraded community lands.
They wanted to understand how their growth projections aligned with real-world biomass patterns. Medius Earth had already done a lot of great work, and by sharing relevant information and their deep expertise on the project, we were able to update our assumptions and make them more accurate. For example: The starting diameter had to be higher than our original assumptions as the plants were first grown in a nursery (a vintaging strategy)
We started by analysing project details (tree species, allometric equations, tree count, location) and built a 30-year sequestration curve based on our model. Comparing it with Medius Earth’s, we found:
Sequestration Curve – We analysed the biomass growth projections and found that Medius Earth’s model had higher carbon credit issuance in the first few years, whereas our curve showed a more gradual sequestration pattern.
Survival Rate – Medius Earth used two survival rate scenarios. The Medius higher survival rate scenario (including replanting to replace lost trees) assumed a higher surviving trees per hectare at Year 10, but our model, which links diameter, height, and mortality, estimated a lower number per hectare.
Credit Issuance – We assessed how different survival and growth assumptions impacted carbon stock projections and long-term credit issuance.
How Does This Help?
Provided a sequestration curve for comparison, highlighting where early-year sequestration rates differed.
Clarified how survival rates impact long-term carbon stock, ensuring realistic growth trajectories.
Helped refine credit issuance assumptions, giving Medius Earth confidence in their model’s viability.
With this information, Medius Earth gained more confidence that their sequestration model was not overly optimistic. They identified that using an Artio curve could still generate 15% -20% equity returns under market range assumptions in excess of $60 per VCU post 2031, proving both the scientific and financial strength of their project.
After our assessment and in-depth discussions analysing allometrics, survival rates and data sources, Medius Earth revisited their assumptions. The area for particular attention was the sequestration in early years in the Medius curve (partly driven by a vintaging strategy to planting older saplings). Medius Earth implemented shared learnings and made adjustments to their own model primarily by incorporating lower survival rate estimates. The final output can be seen below, illustrating a closer convergence of curves after 2030 (when carbon certificate verification is scheduled to occur):
Figure 1. Carbon curve comparison
Refining these models is key to ensuring carbon projects are scientifically credible, investable, and insurable. It’s been great working with Medius Earth, and we look forward to seeing the positive impact of their project moving forward!
If you’d like to learn more about our work supporting ARR projects please book a call here.
