CARB forest offset crediting is conservative

Yesterday, California’s Air Resources Board held a public workshop to discuss the forest offset protocol and emerging science.  Big takeaways from a series of presentations by protocol experts and forest scientists include the inherent conservativeness of protocol crediting, the effectiveness of the common practice values for setting baseline floors, the likely over-contribution of buffer credits for wildfire risk, and the need to reduce costs to increase small landowner access.

Arguably, the most significant takeaway from the workshop was an illustration of the protocol’s inherent conservativeness in calculating credits, which are ultimately only a subset of the total greenhouse gas benefit of forest projects:

Perhaps the second-most important point was that most of the forestry projects’ minimum baseline values are at the common practice value. This indicates that while financial and legal analysis could justify more timber harvesting in the baseline, the common practice values are appropriately functioning as a baseline floor and guarantor of additionality.

Recently published research by Oregon State University’s Professor Mark Harmon was also highlighted. This field-based study found that in high severity fires (basal area mortality >75%), above ground woody biomass combustion is only 1.2% – 3.2% at the stand level.  This indicates that buffer credit retirements following wildfire may be overly conservative because much of the biomass is actually moving into woody debris and soil carbon pools rather than being emitted into the atmosphere.

Discussions also highlighted the need to reduce costs while maintaining high levels of stringency to increase carbon market access for small landowners.  Adjustments to required verification intervals, allowing technological solutions to augment field-based inventory and verification, and allowing total forest volume statistical tests instead of sequential plot tests during verification were all referenced.

1. CARB Workshop Materials
2. Harmon, Mark E., Chad T. Hanson, and Dominick A. DellaSala. 2022. “Combustion of Aboveground Wood from Live Trees in Megafires, CA, USA” Forests 13, no. 3: 391.