## 4 Discussion
Analysis of third-party verification of the CARB-CAR forest carbon supply chain revealed inconsistencies with CARB-CAR policy, including: (1) The CARB-CAR Howland project did not meet CARB reporting regulations for both tranches of Howland CARB offsets as an early action project (CAR681), or as an ARB compliance project (CAR1661), by noncompliance of offset verification reporting dates (Supplement Table S5, Supplement Document S6); (2) CAR misstated the actual values for a single year of NEE data (1996) [41] as seven years of seasonal Howland NEE data in support of CAR model adjustment for seasonal trends in tree growth. However, the CAR model (v. 3.2) excludes terms for soil carbon as ecosystem respiration, intrinsic to NEE data, and requires conversion of NEE micromodes m\({}^{-2}\) s\({}^{-1}\) to tree volume, a complex topic addressed by [69]. Details of model revisions and results were not provided, calling the validity of model results into question; (3) The Howland NEE and soil GHG records, advancing annually from 1996 to 2021, were available to CARB-CAR project owners, operators, and third-party verifiers (38,40,41,43,44,55,58,59,60) overlapping with the supply chain process from 2013 to 2019 culminating in serialized CARB verified offsets according to the AB32 mandate [70]. The Howland US-Ho1 NEE data were not reported as an independent check of the CARB-CAR annual results, a comparison that would have constrained the natural ranges for carbon sequestration offering an opportunity to proscriptively avoid CARB-CAR forest carbon sequestration uncertainties; (4) The Howland CARB-CAR project reporting exhibits errors and lapses in recordation, similar to those reported previously [1], including numerical errors, changes in reporting format from annual to discretionary mixed time intervals, and non-standard model operations resulting in uncertain values; and, (5) The raw data and detailed model outputs for the CARB-CAR projects have not been made available to the public, limiting collaboration and external verification of the project results. Instead, the CARB-CAR data and information are housed on personal computers with no central repository (Supplement Table S5, Item 10). Considering the uncertainties identified above, the CARB-CAR verification process is scientifically unjustifiable, creating avoidable offset invalidation risk for CAR681 and CAR1161. The exclusion of direct measurement protocols for forest carbon has been recently extended within the Assembly Bill AB398 [71] the successor bill to AB32 [70], by recommendation of a mandated Task Force to guide inclusion of new offset protocols. However, direct measurement of forest carbon protocols was not addressed [72]. The CARB-CAR and similar protocols could be improved by defining measurement and model results within Equation (1) universal reference framework (NEE = R\({}_{\text{eco}}\) + GPP) and incorporating independent field data for direct measurement of CO\({}_{2}\). Collaboration with forest carbon sequestration field sites represented by the National Ecological Observatory and the AmeriFlux network of eddy covariance towers [73,74] may suggest improvements in the CARB-CAR protocol. Given the sources of uncertainty identified for the CARB-CAR verification process, improvements could be implemented in the near term, such as providing raw data availability for external users, inter-comparison of CARB-CAR with NEE data where possible, enforcing accounting standards, and adherence to consistent reporting formats.