Blue carbon ecosystems (BCEs) remove carbon dioxide from the atmosphere and store significant amounts of organic carbon (OC) in their soils. Consequently, the protection and restoration of BCEs may contribute to net greenhouse gas emissions abatement and help address the global challenges of both mitigating and adapting to climate change. An ongoing debate is whether OC sequestered out with the blue carbon (BC) project and transported to its present location (allochthonous) should be counted as ‘additional’. There are inconsistencies in the treatment of allochthonous carbon between BCE methodologies, potentially undermining the credibility of global BC accounting initiatives. To explore these inconsistences, we compare the methodologies which we were able to find online, with particular focus on the VERRA, IPCC and BlueCAM methodologies, and review the science underlying any approach to account for allochthonous OC. Our findings indicate that there are currently no robust scientific approaches to define an appropriate apportioning of allochthonous OC for discounting in the calculation of additionality. We therefore advocate for the inclusion of allochthonous OC in BC crediting projects when an observational and experimental approach does not support the calculation (and discounting) of the refractory allochthonous carbon contribution.

中文翻译：

---

蓝碳生态系统的额外性：普遍适用的会计方法的建议


蓝碳生态系统 （BCE） 从大气中去除二氧化碳，并在土壤中储存大量有机碳 （OC）。因此，保护和恢复 BCE 可能有助于减少温室气体净排放，并有助于应对缓解和适应气候变化的全球挑战。一个正在进行的争论是，与蓝碳 （BC） 项目一起隔离并运输到现在的位置 （allochthonous） 的 OC 是否应该算作“额外”的。BCE 方法之间对异质碳的处理存在不一致，这可能会破坏全球 BC 会计计划的可信度。为了探索这些不一致之处，我们比较了我们在网上能够找到的方法，特别关注 VERRA、IPCC 和 BlueCAM 方法，并回顾了解释异质 OC 的任何方法的基础科学。我们的研究结果表明，目前没有强大的科学方法来定义在额外性计算中用于贴现的异度 OC 的适当分配。因此，当观察和实验方法不支持计算（和贴现）难降解的异碳贡献时，我们主张将异质 OC 纳入 BC 信用项目。