Modeling the net carbon balance is challenging due to the knowledge gaps in the variability and processes controlling gross carbon fluxes. Terrestrial carbon cycle modeling is susceptible to several sources of bias, including meteorological uncertainty, model structural uncertainty, and model parametric uncertainty. To determine the impact of these uncertainties, we compare three model‐derived representations of the global terrestrial carbon balance across 1997–2009: (1) observation‐constrained model‐data fusion (CARBon Data Model FraMEwork, CARDAMOM), (2) the reanalysis‐driven Trends in Net Land‐Atmosphere Carbon Exchange (TRENDY) land biosphere model ensemble, and (3) the Coupled Model Intercomparison Project 5 (CMIP5) Earth System Model ensemble. We consider the spread in carbon cycle simulations attributable primarily to parametric uncertainty (CARDAMOM), structural uncertainty (TRENDY), and combined structural and simulated meteorological uncertainty (CMIP5). We find that the spread across the CARDAMOM ensemble long‐term mean—produced by parameter uncertainty—is larger than the spread of TRENDY and CMIP5 for net biosphere exchange (NBE) but similar for gross primary productivity (GPP). The carbon flux dynamics of CARDAMOM compares to models in TRENDY as well as models in TRENDY compare to each other in many regions for NBE seasonal (nine of 12), NBE interannual (11 of 12), and GPP seasonal variability (7 of 12), although not for GPP interannual variability (2 of 12). The simple model structure of CARDAMOM and systematic assimilation of observations is sufficient to produce carbon dynamics within the range of more complex models. These results are encouraging for the use of model‐data fusion products with empirically estimated uncertainty for global carbon cycle studies.

中文翻译：

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来自相对简单生态系统模型的同化数据的碳通量变异性与陆地生物圈模型估计值一致

由于可变性和控制总碳通量的过程中存在知识空白，对净碳平衡进行建模具有挑战性。陆地碳循环建模容易受到多种偏差因素的影响，包括气象不确定性，模型结构不确定性和模型参数不确定性。为了确定这些不确定性的影响，我们比较了1997-2009年间三种模型得出的全球陆地碳平衡的表示形式：（1）观察约束模型-数据融合（CARBon数据模型FraMEwork，CARDAMOM），（2）重新分析净土地-大气碳交换（TRENDY）土地生物圈模型集合的趋势；以及（3）耦合模型比较项目5（CMIP5）地球系统模型集合。我们认为碳循环模拟中的扩散主要归因于参数不确定性（CARDAMOM），结构不确定性（TRENDY）以及组合的结构和模拟气象不确定性（CMIP5）。我们发现，由参数不确定性产生的整个CARDAMOM集合长期平均值的散度大于TRENDY和CMIP5的净生物圈交换（NBE）散度，但对于总初级生产力（GPP）相似。在许多地区，NBE季节性（12个中的9个），NBE年度（12个中的11个）和GPP季节变化（12个中的7个）中，CARDAMOM的碳通量动态与TRENDY中的模型进行比较，以及TRENDY中的模型相互进行比较，但不适用于GPP年际变化（第2个，共12个）。CARDAMOM的简单模型结构和观测值的系统同化足以在更复杂的模型范围内产生碳动力学。这些结果对于将模型数据融合产品用于实证评估的不确定性在全球碳循环研究中的使用是令人鼓舞的。