California air resources board forest carbon protocol invalidates offsets

CARB-CAR

The CARB-CAR population data used in this study represent 63 sites covering 340 site years, primarily located in the US temperate zone, and have been assigned CAR serial numbers to project offsets (units: gC m⁻²yr⁻) (Table 1, Supplemental Informations 1,3–7 for site information and data). The CARB-CAR projects listed in Table 1 were sourced from the California Air Resources Board and the California Environmental Protection Agency website pages as noted for “Early Action Projects” (California Air Resources Board, 2015c) and as ARBOC’s issued as of 09-01-2018, and must adhere to CARB-CAR forest management protocols. Forest project data were accessed through links to a Climate Action Reserve project identification number (CAR#) providing a project summary page, a document summary page and a cumulative performance report page. The data used in this analysis was sourced directly from the Cumulative Performance Report page and from the column of Verified GHG Reductions for each year of each project or as otherwise reported on the project page when a Cumulative Performance Report was not available (Table 1). We reviewed CARB-CAR registry records and history for each project noting discretionary inconsistencies in protocol reporting and process (Table 1). The CARB protocols and accounting requirements are described in three related primary documents published in 2011 (California Air Resources Board, 2014), 2014 (California Air Resources Board, 2014) and 2015 (California Air Resources Board, 2015b) entitled: “Compliance Offset Protocol U.S. Forest Projects”. The underlying equations for the CARB-CAR protocol are reviewed (Supplemental Information 8) to identify carbon accounting terms and to establish similarities with related protocols including the American Carbon Registry (ACR) (Winrock International, 2016), the Clean Development Mechanism (CDM) (Warnecke, 2014) and the Verified Carbon Standard (VCS) (Verified Carbon Standard, 2018). The CARB-CAR protocols employ limited forest mensuration practice (e.g., forest survey every six years or longer, up to 12 years; California Air Resources Board, 2015b; Marland et al., 2017), vegetation proxies (Cawrse et al., 2009), estimated baselines and growth simulation models (California Air Resources Board, 2011; Climate Action Reserve, 2018b) to determine net forest carbon sequestration. Direct measurement of CO₂ in the field does not occur at any point of the protocol process. Additional details are available in the endnotes.³

NEE

NEE population data, described by Baldocchi, Chu & Reichstein (2018), and Baldocchi & Penuelas (2019), herein referred to as NEE1 and NEE2 (units: gC m⁻²yr⁻¹), respectively, were employed to assess validity of CARB-CAR results representing direct measurement of CO₂ flux. The NEE1 population data represent 59 eddy covariance tower sites, primarily within the US and Canada, with a total of 540 site years. The NEE1 project annual data, employed for the analyses presented, was sourced from each of the NEE1 site references and cross-checked with the NEE1 published data for each site. (see Supplemental Information 1, 3–7 for site information and data) and utilized for comparison with CARB-CAR project interannual data. NEE is also expressed as Net Primary Productivity (NPP) where the term—NEE is employed (Chapin et al., 2006). NEE is a meteorologically based direct measurement method, deployed in the field, integrating all forest CO₂ fluxes (e.g., above and below ground) and is methodologically independent of the model and estimation-based CARB-CAR protocol. We provide a graphical interpretation of the NEE1 data in Supplemental Information 9, illustrating the relationship and relative magnitude for NEE (open rectangle, right axis), GPP and R_eco (open circles), filled and gray rectangle symbols represent NEE1 data for the Howland Forest, Maine, USA (Ho-1), and the Wind River (Wrc), Washington, USA, sites, respectively, illustrating overlapping and narrow ranges for diverse forests (e.g., west coast redwoods versus east coast hardwoods). NEE, GPP and R_eco values falling outside of the known ranges likely do not reflect natural and managed forest ecosystems and are a sign of inaccurate estimates and a basis for invalidation. NEE2 data, inclusive of NEE1 data, expand the GPP, R_eco and NEE population database for ecologically diverse natural and managed forests across 155 global observation platforms representing 1,163 site years. NEE1,2 data are derived from measurement of gaseous molecular CO₂ vertical fluxes (Baldocchi, Chu & Reichstein, 2018; Baldocchi & Penuelas, 2019) and are based on globally applied and standardized eddy covariance methods (Baldocchi, 2003; Baldocchi, 2014) to quantify NEE (Chapin et al., 2006; Luyssaert et al., 2009) as tCO₂e or gC m⁻²yr⁻¹. NEE data, available from the Fluxnet database (Fluxnet, 2019), are routinely employed to test significance of trends for forest growth (Ney et al., 2019), soil and ecosystem respiration (Bond-Lamberty & Thomson, 2010; Göckede et al., 2019), fire disturbance (Rocha & Shaver, 2011) and effects of climate change on diverse ecosystems (Yu et al., 2019), similar to the analytical approach employed in this report. Additional information for NEE projects is described in the endnotes.⁴

Statistical calculations

Individual annual records (units: gC m⁻²yr⁻¹) were used in this analysis; trends in time series are not considered. Our analysis is based on population data for NEE, GPP and R_eco (NEE1,2) representing primarily diverse temperate zone forest ecosystems (Supplemental Information 9) of the world. The tight coupling between GPP and R_eco constrains NEE within relatively narrow boundaries (mean, standard deviation) considering the global spatial and annual time scales reported (Baldocchi & Penuelas, 2019); values falling outside the NEE1,2 boundaries are likely inaccurate, and with additional criteria may be considered invalid. Although only a single location, the Howland Forest, shares application of both NEE and CARB-CAR protocol, an accurate measurement of net carbon sequestration for any location is expected to comply with the NEE, GPP and R_eco relationship (Supplemental Information 9, filled and gray rectangle symbols for Howland Forest and Washington, GPP and R_eco, respectively). Each data point (whether in NEE or CARB-CAR) comes from the underlying population of the world’s forests (e.g., managed or conserved) providing the basis for the two-sample statistical tests presented. We employ standard statistical tests to compare population characteristics, including the accuracy in means and precision (i.e., interannual range) for the CARB-CAR protocol methods, relative to directly measured NEE1,2 sample annual values and variance. See Supplemental Information 2 for details of the statistical analyses.

Box plots

Figure 1A shows the difference in distribution, measures of central tendency and outliers between the CARB-CAR and NEE1 populations for net forest carbon sequestration. A selected interval of the box plot excluding the CARB-CAR outliers is presented in Fig. 1B to illustrate the population differences (CARB-CAR median of −445.4 gC m⁻²yr⁻¹ compared to the NEE1 median value of −172.5 gC m⁻²yr⁻¹ ) corresponding to the larger spread and left-skewness of CARB-CAR values. The sample means and standard deviations (±), for all annual values, Fig. 1A, of the CARB-CAR and NEE1 datasets are, respectively, −948.8 ± 1,504.8 gC m⁻²yr⁻¹ and −198.0 ± 261.6 gC m⁻²yr⁻¹ representing an extreme range of ∼5× the value for CARB-CAR forest carbon sequestration mean and ∼6× standard deviation for interannual variance relative to the NEE1 population data (Baldocchi, Chu & Reichstein, 2018). The difference in mean values between the two populations is significant at the 95% confidence level, rejecting the null hypothesis that the CARB-CAR population mean falls within the NEE1 population mean. The mean and standard deviation of the NEE2 data are −156 ± 284 gC m⁻²yr⁻¹, respectively (155 sites; 1,163 site year), supporting the comparison with CARB-CAR data and ∼6× the CARB-CAR mean and ∼5× the standard deviation characterizing interannual ranges for natural and managed forest ecosystems. NEE1,2 natural variation for global forests across management activities is constrained tightly by GPP and R_eco (Supplemental Information 9) providing boundaries for NEE comparisons.

Difference between means

Figure 2 shows a plot of the 95% confidence interval for the difference in means between the CARB-CAR and NEE1 population of (Baldocchi, Chu & Reichstein, 2018) annual measurements for all years available and for the selected years of 2007 and 2008. Given the large difference in sample means for the CARB-CAR and NEE1 datasets the true population means may also be significantly different. We test the null hypothesis that the two sample populations were drawn from the same underlying population of annual values for forests. The combined data set consists of 340 CARB-CAR and 540 NEE1 data points (“Total”), each reported as representing an annual cycle determined by each protocol. A formula for a large-sample confidence interval is used for the bar labeled “Total”; no assumption on equal standard deviations between the two data sets has been made. Amongst the years with overlapping data (2001–2014), we choose 2007 and 2008, as they have the largest number of combined sample points, 65 in 2007 (23 for ARB and 42 for NEE1) and 65 in 2008 (24 for ARB and 41 for NEE1), excluding initial year values. The null hypothesis that the two data sets come from the same population is rejected implying that CARB-CAR protocols reflect anomalous values and cannot be relied upon to manage forest carbon sequestration. The 5% estimation error does not overlap with the 95% confidence interval demonstrating that the CARB-CAR estimates are more than the allowed 5% from the NEE1 population values. The standard deviation for the CARB-CAR data is very large compared to the NEE1 standard deviation, irrespective of the year. For example, in 2008, the standard deviations for CARB-CAR and NEE1 were respectively, 1,170 and 255 gC m⁻²yr⁻¹, a ∼5× over-estimation difference for interannual NEE1 values. This leads to a very wide confidence interval that also establishes that the CARB-CAR project data are invalid based on the permitted 5% compliance margin of error. To our knowledge, CARB-CAR compliance testing of project results has not been reported employing directly measured forest CO₂.

Project annual interval plot

Figure 3 shows a time interval plot of CARB-CAR annual data from 2002 to 2015 and NEE1 (note: NEE values are illustrated as positive for the purposes of this graph) annual measurements (Baldocchi, Chu & Reichstein, 2018) from 1992 to 2015 to further test the invalidation of CARB-CAR offsets according to the 5% invalidation compliance rule. The averages for the two data sets are shown by each vertical bar representing forest carbon sequestration calculated annually over all available locations. The selected intervals are absent first year data for the CARB-CAR population to present a conservative case for testing the null hypothesis. The year 2006 was selected, in which the largest average carbon offset by CARB-CAR sites (n = 12) has been recorded, namely −2,038 gC m⁻²yr⁻¹, and apply the corresponding 5% admissible error of 101.9 gC m⁻²yr⁻¹ to all CARB-CAR years, shown as error bars for each CARB-CAR year. No intersection between the admissible interval and the actual NEE1 measurements for any of the overlapping years (2001–2015) is observed. The NEE1 averages through the interval are consistent relative to the large year-to-year fluctuations observed for the CARB-CAR dataset. The null hypothesis is rejected; the CARB-CAR data are invalid by exceeding the 5% compliance threshold for the years represented in this analysis. The absence of negative values, in this case representing CO₂ emissions to the atmosphere, implies that the CARB-CAR protocol is biased against detection of a switch from net sequestration to net positive emissions, arguably a criterion for invalidation.

p-values table

Table 2 shows the results of a null hypothesis that the difference between the CARB-CAR and the NEE1 annual means is under the allowed 5% threshold. A year-by-year detailed comparison between the population data sets to further test the 5% invalidation threshold for the CARB-CAR data is presented. The test is performed separately for all years between 2002 and 2015; p-values are recorded in the last two rows of Table 2. The p-values range from 0.00 to 0.065. Typically, p-values ≤5% demonstrate a rejection of the null hypothesis. The results reject that the estimation error is within the allowed 5% value, with three exceptions to the 14-year record. In the case of years 2004, 2013 and 2014, the p-values are higher than 5% (i.e., 6.53%, 5.48% and 5.24%). However, in these cases (i.e., 2004; p = 0.065, 2013; p = 0.055, 2014; p = 0.052) the probability that the CARB-CAR data were not out of the norm is only 1.87 × 10⁻⁴%, supporting the null hypothesis rejection. Variation in annual p-values is expected according to the number of data points included per year represented as overlapping intervals.

Howland forest survey protocol comparison

The Howland Research Forest Carbon Project (CAR681) represents the only case in which CARB-CAR and Ameriflux (Ho-1) NEE data are available for the same project location, land area (552 acres; 233.4 hectares), and across shared time intervals (2003–2013) allowing direct comparison of results. Comparability of the Ho-1 NEE1 and CAR681 data is established by the location of two eddy covariance towers within the CARB-CAR survey areas. Half-hourly and integrated annual carbon exchange values recorded at the separate Howland towers were similar, with average annual net carbon uptake differing between the two towers by <6% (Hollinger et al., 2004; Hollinger et al., 2013; Richardson et al., 2019) (see Supplemental Information 10 for project area map, sampling locations and CAR681 webpage offset data; Table 1).

CAR681 methodology and calculations described below are reported in the Project Design Document (PDD, published 12-03-2014) (see Table 1, link to CAR681 project page). Results for CAR681 include data for the period 2008 to 2013 as hindcasted and reported in 2014; a timber inventory was completed in October 2013. The CAR681 Protocol excludes soil carbon (Table 1, FM-6) (California Air Resources Board, 2015b) (PDD, pp. 10, 19), employs the common practice method to model onsite above ground carbon stocks of 46 tCO₂e acre⁻¹ (18.6 tCO₂e hectare⁻¹) (PDD, p. 33), and established a timber re-inventory interval of 12 years. Model operation (protocol version CARv3.2) included growing the inventory forward 5 years to 2018, then de-growing the inventory to align with the 10∕8∕2008 start date. Reduced growth rates were selected and employed in model runs to establish the project baseline through a series of estimated growth and harvesting scenarios over 100 years. CAR681 results are available on the CAR website page: Cumulative Performance Report (Table 1, Supplemental Information 10).

Carbon sequestration for the initial CAR681 vintage year, 2008, is reported as −43,687.0 tCO₂e, or −5,334.7 gC m⁻²yr⁻¹, ∼26× in excess of the reported NEE1 population mean (e.g., −198.0 gC m⁻² yr⁻²) and ∼34× the NEE2 population mean (e.g., −156 gC m⁻² yr⁻²) (Supplemental Information 9, filled rectangle symbol). Subsequent vintage years, 2009 to 2013, were invariant with exact values of −1,033.00 tCO₂e, or −126.1 gC m⁻²yr⁻¹. CAR681 data for the interval 2008 to 2013 yield a mean and standard deviation of −994.0 ± 2,126.1 gC m⁻²yr⁻¹, respectively. The total CAR681 offsets issued equal 48,852 tCO₂e (Table 1, Supplemental Information 10, CAR681 Project Page, Cumulative Performance Report). CAR681 results were audited and approved (see link, Table 1). Serial numbers were assigned to offsets on 03∕13∕2015 (Table 1, Supplement S8).

In contrast, Ho-1 NEE for 2008 was reported as −287.1 gC m⁻²yr⁻¹ (Hollinger et al., 2013; Hollinger et al., 2016), ∼19× smaller compared to the 2008 CAR681 value, representing an over-estimation error of ∼1,757% (e.g., footnote 2). The CAR681 result clearly exceeds the 5% CAR invalidation threshold criteria and is arguably invalid. Ho-1 NEE values for the years 2009 to 2013 ranged from −191.9 to −330.9 gC m⁻²yr⁻¹ with a mean and standard deviation of −255.02 ± 57.7 gC m⁻²yr⁻¹, respectively (Hollinger et al., 2016), reflecting typical interannual ecosystem carbon dynamics. In contrast, the CAR681 model values for 2009 to 2013 were invariant, a trend not observed for NEE1 sites. The CAR681 subsequent year data are in error, on average by 50% less, compared to the Ho-1 NEE1 data, an exception for the CARB-CAR population, a trend resulting from selection of model parameters. Ho-1 NEE for the 2008–2013 period totals ∼13,446 tCO₂e in contrast to 48,852 tCO₂e based on the CARB-CAR protocol. Ho-1 NEE data for the period 1996 to 2002 and 1996 to 2008 (Hollinger et al., 2004; Hollinger et al., 2013) have not been compared to CAR681 data. CAR681 results (−994.0 ± 2,126.1 gC m⁻²yr⁻¹) do not reflect Ho-1 directly measured mean or interannual values (−255.02 ± 57.7 gC m⁻²yr⁻¹) and cannot be ignored as criteria for invalidation. However, if CARB-CAR data is interpreted as approximating GPP (e.g., not NEE), and ∼82% of assimilated carbon is lost as ecosystem respiration (Hollinger et al., 2013; Hollinger et al., 2016; NEE1,2), an approximate correction to the CARB-CAR data reduces the mean Howland NEE1 and CARB-CAR population values to ∼−179 and ∼−170 gC m⁻²yr⁻¹, respectively, similar to the NEE1 (e.g., −198 ±261.6 gC m⁻²yr⁻¹) and NEE2 (e.g., −156 ± 284 gC m⁻²yr⁻¹) population means. The high variance for interannual CARB-CAR results (e.g., ± 1504.8 gC m⁻²yr⁻¹) cannot be adjusted based on the correction, nor is the correction proposed as a universal revision to individual CARB-CAR projects. However, the adjustment generally supports the results presented here recognizing that R_eco is absent from CARB-CAR carbon accounting (Supplemental Information 8). This comparison emphasizes the difficulty of determining soil carbon efflux and R_eco terms with CARB-CAR protocol tools; the NEE method integrates GPP and R_eco fluxes providing NEE (e.g., NEE1,2, Supplemental Information 9).

The financial and carbon market consequences for the CAR681 offset errors are substantial. Assuming a 2015 average price of $9.70 USD per offset credit (tCO₂e) (Hammrick & Gallant, 2017), sale of CAR681 offsets equal ∼$473,864 compared to $130,431 for Ho-1 NEE based offsets, a difference of $343,433. Overpayment of ∼4× for Howland Forest offsets establishes carbon asset value loss and error in subsequent financial transactions including a debit to the AB32 compliance carbon ledger. The initial vintage year overcrediting results from selectively establishing the Common Practice above-ground standing live carbon stock (e.g., 46 tCO₂e acre⁻¹; 31 tC ha⁻¹) to ∼4× below the independently determined value for the site (119–150 tC ha⁻¹; Hollinger et al., 2013). The CARB-CAR estimated baseline scenario maximizes credits generated in the initial year that cannot reflect known rates of CO₂ removal from the atmosphere (e.g., 5,332.3 gC m⁻²yr⁻¹, ∼26× in excess of the reported population annual mean NEE1 data of e.g., −207.99 gC m⁻² yr⁻², and ∼34× the population annual mean NEE2 data of −156 gC m⁻² yr⁻²). Lowering the Common Practice value relative to actual standing carbon stock for Howland Forest, incorrectly attributes historic carbon (e.g., unknown years of cumulative forest growth prior to the project) to a single vintage initial year of carbon sequestration. In effect, this results in higher initial year crediting, consistent with independent error analyses of similar CARB-CAR projects (Dunlop, Winner & Smith, 2019; Haya, 2019; Haya et al., 2016).

In contrast, Ho-1 NEE increased by ∼6 gC m⁻²yr⁻¹ over the last 19 years, representing ∼50% overall increase of forest carbon sequestration; each year represents an annual baseline relative to net negative or net positive emissions to the atmosphere (Hollinger et al., 2013; Richardson et al., 2019). There is no initial-year front loading of historic carbon. The time series trend for Ho-1 would not be detected based on the CARB-CAR invariant annual data (excluding first year data), emphasizing the importance of trend detection sensitivity for carbon sequestering ecosystems. Ho-1 provides extensive data to test CARB-CAR protocols including process-based model development (Sihi et al., 2018), independent direct measurement of soil CO₂ efflux and ecosystem respiration (Giasson et al., 2013), contemporaneous NEE for CO₂, CH₄ and N₂O (Richardson et al., 2019), response to shelterwood harvest (Scott et al, 2004) and diverse ecological data (Giasson et al., 2013). In summary, incomplete carbon accounting, model-based overcrediting carbon offsets by >5% relative to actual values, and demonstration that the CARB-CAR results do not agree with actual forest carbon sequestration, invalidate the CARB-CAR protocol for this project. Claimed reductions in net CO₂ emissions, carbon offset creation and carbon market transactions cannot be validated with the available data for CAR681 supporting a material misstatement calculation as defined in the AB32 rules (California Air Resources Board, 2013b) (endnote 2).

CARB-CAR project review

Table 1 summarizes the CARB-CAR project sites (n = 63) and attributes considered in this study. Links to serial numbers for specific year vintage offsets issued and to summary pages of the CAR online documentation are provided. Features of the CARB-CAR carbon accounting process are identified and documented: (1) exclusion of the soil carbon pool and soil and ecosystem CO₂ emissions as respiration for the 63 CARB-CAR projects (Methods, CARB Protocols) cited in this study, (2) projects that record and assign serial numbers to offsets for single vintage year carbon sequestration but are based on records of partial or multiple years of carbon sequestration (63 instances), (3) arbitrary model operations initiated and executed as forward and/or backward runs relative to the project start date (33 instances), and (4) excess initial year project carbon sequestration values (31 instances). Considerable discretion by CARB-CAR stakeholders appear to explain protocol inconsistencies; documentation for revisions is not provided. Protocol discretion, including increasing acceptance of default values for protocol components have been documented for related protocols (Kollmuss & Fussler, 2015) consistent with CAR -CAR protocol observations reported here.

Survey of CARB-CAR linked protocols

Similar expressions are employed in the ACR, CDM and VCS protocols (Supplemental Information 8) extending the CARB-CAR carbon accounting uncertainty to large-scale forest carbon projects such as the UN-REDD and REDD+ (United Nations Framework Convention on Climate Change (UNFCCC, 2019), herein referred to as REDD+. REDD+ approved projects rely on the VCS (Supplemental Information 8). Methodologies developed under the United Nations CDM accepts projects and programs registered and approved by the VCS such as method VM0007 REDD+ Methodology Framework (REDD-MF), v1.5 (VERRA, 2015). Technical reports for REDD VCS applications categorically exclude forest soil carbon and ecosystem respiration (e.g., AC-6) from carbon accounting (UNFCCC, 2017) (Table 1). The implementation of REDD in Ghana, Africa, for example, is subject to impacts of potential invalidation for projects (Asante et al., 2017; Kagombe et al., 2018; McFarland, 2018) including World Bank sponsored bond programs similar to that operating in Kenya, such as the Kasigau Corridor project (McFarland, 2018), also based on VCS protocols. Results for REDD+ programs appear to be uncertain, in part, due to carbon offset monitoring and economics (Foss, 2018). Incomplete carbon accounting implies that results for REDD+ net forest carbon sequestration may not be verifiable or capable of identifying net annual ecosystem carbon change in response to reduced deforestation, climate and anthropogenic forcing, and may not be well suited for carbon pricing and trading of carbon financial instruments. Despite carbon accounting limitations, compliance carbon trading platforms and pricing initiatives are rapidly expanding (e.g., 45 national, 25 subnational jurisdictions; World Bank and Ecofys, 2018) emphasizing the importance of improved, shared methodology for forest carbon sequestration product offerings. Although it is not clear how REDD+ will be integrated within the Paris Agreement (e.g., Article 6) (Schneider & La Hoz Theuer, 2018) or into existing compliance markets (Hein et al., 2018), improved quantification of forest carbon sequestration would link REDD+ entities and mechanisms together in a harmonized universal science-based transactional framework. Macroeconomic trends consistent with offset invalidation risk for voluntary and carbon trading markets are provided in endnote.⁵

CARB-CAR CA site data

The CARB-CAR project sites within California, representing 31 of the 63 projects (Table 1), represent a mean and standard deviation of −1,163.2 ± 1,889.8, respectively, more negative and variable than values for the CARB-CAR population data set (63 projects) of −948.8 ± 1,504.8 gC m⁻²yr⁻¹. The CA sites establish the anomalous nature for this group relative to NEE1 (−198.0 ± 261.6 gC m⁻²yr⁻¹) (Supplemental Information 9) and NEE2 (−156.0 ± 284.0 gC m⁻²yr⁻¹) with up to ∼7× the mean and ∼12× the standard deviation (e.g., interannual variance) relative to NEE2 population values. The CARB-CAR sites are located generally within the western mountain biome and the marine coastal zones. The CARB-CAR biomes extend from southern to northern California to Oregon and Washington (Supplemental Informations 1, 9, filled gray rectangle symbol), with similar ecological patterns to support characteristic forest species. The CARB-CAR CA sites report invariant values (i.e., interannual variance of 0.0) for CAR590 (5 of 5 years), CAR694 (5 of 7 years), and CAR935 (12 of 14 years), that do not reflect natural forest ecosystems. Direct overlap of CARB-CAR and NEE methods is not required to establish the anomalous features of forest growth implied by the results for CARB-CAR CA sites relative to known population values. An accurate measurement of net carbon sequestration for any forest location is expected to comply with the GPP vs R_eco relationship for NEE1 (Supplemental Information 9, filled black and gray rectangle symbols for west and east coast forest values as described) and NEE2 (e.g., −156.0 ± 284.0 gC m⁻²yr⁻¹). The CARB-CAR CA project sites according to the statistical analysis of NEE1 sites (e.g., Figs. 1–3, Table 2) and comparison with NEE1,2 data, indicate that the CARB-CAR CA sites do not represent realistic forest carbon sequestration and are arguably invalid.