We show that transport differences between two commonly used global chemical transport models, GEOS‐Chem and TM5, lead to systematic space‐time differences in modeled distributions of carbon dioxide and sulfur hexafluoride. The distribution of differences suggests inconsistencies between the transport simulated by the models, most likely due to the representation of vertical motion. We further demonstrate that these transport differences result in systematic differences in surface CO2 flux estimated by a collection of global atmospheric inverse models using TM5 and GEOS‐Chem and constrained by in situ and satellite observations. While the impact on inferred surface fluxes is most easily illustrated in the magnitude of the seasonal cycle of surface CO2 exchange, it is the annual carbon budgets that are particularly relevant for carbon cycle science and policy. We show that inverse model flux estimates for large zonal bands can have systematic biases of up to 1.7 PgC/year due to large‐scale transport uncertainty. These uncertainties will propagate directly into analysis of the annual meridional CO2 flux gradient between the tropics and northern midlatitudes, a key metric for understanding the location, and more importantly the processes, responsible for the annual global carbon sink. The research suggests that variability among transport models remains the largest source of uncertainty across global flux inversion systems and highlights the importance both of using model ensembles and of using independent constraints to evaluate simulated transport.

中文翻译：

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量化大气传输不确定性对 CO 2 表面通量估算的影响


我们表明，两种常用的全球化学品输运模型 GEOS-Chem 和 TM5 之间的输运差异导致了二氧化碳和六氟化硫的模拟分布的系统时空差异。差异的分布表明模型模拟的运输之间存在不一致，很可能是由于垂直运动的表示造成的。我们进一步证明，这些传输差异导致了表面二氧化碳通量的系统差异，这些差异是通过使用 TM5 和 GEOS-Chem 的全球大气反演模型的集合估计的，并受到现场和卫星观测的约束。虽然对推断的地表通量的影响最容易通过地表二氧化碳交换的季节性周期的大小来说明，但与碳循环科学和政策特别相关的是年度碳预算。我们表明，由于大规模输运的不确定性，大纬向带的逆模型通量估计可能具有高达 1.7 PgC/年的系统偏差。这些不确定性将直接传播到对热带地区和北部中纬度地区之间的年度经向二氧化碳通量梯度的分析中，这是了解位置的关键指标，更重要的是了解负责年度全球碳汇的过程。研究表明，输运模型之间的变异性仍然是全球通量反演系统不确定性的最大来源，并强调了使用模型集成和使用独立约束来评估模拟输运的重要性。