## 4 Discussion
The number of projects and areas required (e.g., 10,000-50,000 ha) to achieve the NEE (tCO\({}_{2}\)e 2.76 billion) in this hypothetical scenario is 55,200 compared to ~$67 CDM forest projects recorded since 2006 [74] (see Appendix A, Table A2 for additional details); in contrast there are ~1.5 million farms in the US alone [75]. The forgoing comparison is a stark reminder of the scale of action needed to reverse deforestation. Impediments to expansion of reforestation projects result, in part, from the high cost and invalidation risk to landowners (e.g., exclusion of CO\({}_{2}\) measurement) typical of existing forest carbon protocols [76]. A comparison of features and functions of existing protocols and eddy covariance NEE methods has been reported [5] emphasizing the need for scientific protocol criteria that uncouples pricing constraints fromregulatory and legislative mandates across offset types, equalizing forest carbon project opportunities and earning potential [5] for all landowners including Indigenous People.  
We emphasize that existing forest carbon protocols require that each tCO\({}_{2}\) captured remains fixed in the trees or soil for at least 100 years fulfilling the arbitrary permanence requirement of non-CO\({}_{2}\) based protocols such as the CARB and Climate Action Reserve (CAR) [4; 77; 78]. According to CARB-CAR protocols, landowners who exit the project prior to 100 years must repay the value of all issued offsets in the cases of reforestation and avoided emissions, and pay an additional penalty in the case of improved forest management [7], making exits punitive and infeasible. In contrast, we show here that accounting methods can accommodate realistic temporary carbon capture and storage without arbitrary exit terms [7], delaying total deforestation and the effects of climate change and providing time intervals to take other actions, for example, reforeting \(\sim\)0.9 billion ha of degraded land [79]. The Moura-Costa ton-year accounting method [56] combined with the revised Bern Model for decay of atmospheric CO\({}_{2}\) concentration over time [54] provides viable exit options for shorter projects, an approach endorsed by the IPCC [80]. Furthermore, variance in the no exit case for US-Ha1 is higher than in exited projects (Figure 2 and Table 13 from the Supplemental) emphasizing the variable nature of annual carbon sequestration even over long intervals [81] and the need for direct measurement to validate claims of annual net CO\({}_{2}\) emission reduction for carbon markets by ecosystems, and \(R_{exo}\) as represented by isoflav. This approach incentivizes many of the potential short projects that are outside any existing net forest carbon protocol because the 100-year required project term is a high barrier to entry for landowners reflected in CARB-CAR projects representing less than \(\sim\)0.2% of available US land [4; 77]. Moreover, the implementation of AB398 imposes new changes in offset pricing including an arbitrary price ceiling of $65 per allowance, and requires at least 50% of projects to directly benefit the State of California implying a carve-out for projects that must originate in the state [82]. The consequences of AB398 are not known but suggests a retraction of the CARB-CAR forest carbon protocol from areas outside of California. Clearly, an alternative protocol that catalyzes forest conservation and restoration that is uncoupled from regulatory legislation is needed, such as that presented in this study. The US-Ha1 analysis suggests that short- and long-term forest conservation (e.g., minimal timber removal) is viable and accretive to the forest regeneration process. From a commercial perspective, selection of the optimal project length (Figure 3C) depends on the discount rate that the investor uses to account for the time value of money. While low discount rates (below 5%) incentivize longer projects, making their returns rise exponentially as shown in Figure 3C, a rate above 10% would make these decay after a few years.