Soil organic carbon changes (ΔSOC) are regulated by climate and land use change. Here, we analyze regional and global ΔSOC from 1861 to 2099 based on five terrestrial biosphere model (TBM) simulations of the Inter‐Sectoral Impact Model Intercomparison Project Phase 2b. The TBMs were driven by harmonized gridded land use change and bias‐adjusted climate forcing data from different general circulation models (GCMs) for climate scenarios RCP 2.6 and RCP 6.0. Between 2005 and the end of this century, we estimated an increase of SOC for two scenarios with large uncertainty, which is dominated by differences between TBMs. We present a new emergent constraint approach to constrain future modeled ΔSOC over natural vegetation from RCP 6.0 simulations using recent observed trends of net primary productivity as a proxy of litter inputs to soil pools. Our results showed that the uncertainties in constrained ΔSOC can be reduced in comparison with the original model ensemble, but constrained values of ΔSOC depend on the choice of a GCM and climate regions. For the reduction of the SOC density in areas where cropland expanded (Δsoc_{cropland expansion}) over natural vegetation as a result of land use change, the constrained Δsoc_{cropland expansion} still features large uncertainties due to uncertain observed data. Our proposed emergent constraint approach appears to be valuable to reduce uncertainty on SOC projections, but it is limited here by the small number of models (five) and by the uncertainty in the observational data. Applications to larger ensembles from Earth System Models should be tested for the future.

中文翻译：

---

减少新出现的约束条件下未来全球土壤碳对气候和土地利用变化的不确定性

土壤有机碳的变化（Δ SOC）由气候和土地利用变化调节。在这里，我们分析区域和全球Δ SOC，从1861年到基于五个陆地生物圈模型（TBM）的跨部门影响模式比较计划阶段2b的模拟2099。TBM是由针对气候情景RCP 2.6和RCP 6.0的统一网格化土地利用变化和来自不同通用循环模型（GCM）的偏差调整气候强迫数据驱动的。在2005年至本世纪末之间，我们估计了两种不确定性较大的情况下SOC的增加，这主要是由TBM之间的差异决定的。我们提出了一种新的紧急约束方法来约束未来建模的ΔSOC使用最近观察到的净初级生产力趋势作为垃圾池对土壤池输入的替代，通过RCP 6.0模拟对自然植被进行了研究。我们的研究结果表明，在受限的Δ的不确定性SOC可以与原始模式集合相比，可以减少，但约束Δ的值SOC取决于GCM和气候区域的选择。对于SOC的密度的区域中的缩减，其中农田膨胀（Δ SOC_耕地膨胀）比天然植物为土地利用变化的结果是，受约束的Δ SOC_农田扩张由于观测数据不确定，仍然具有很大的不确定性。我们提出的紧急约束方法对于减少SOC预测的不确定性似乎很有价值，但是在这里它受到少量模型（五个）和观测数据不确定性的限制。地球系统模型在大型合奏中的应用应在将来进行测试。