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首页> 外文期刊>Journal of Geophysical Research. Biogeosciences >Causes and implications of persistent atmospheric carbon dioxide biases in Earth SystemModels
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Causes and implications of persistent atmospheric carbon dioxide biases in Earth SystemModels

机译：地球系统模型中持续存在的大气二氧化碳偏差的成因与影响

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The strength of feedbacks between a changing climate and future CO_2 concentrations is uncertain and difficult to predict using Earth System Models (ESMs). We analyzed emission-driven simulations-in which atmospheric CO_2 levels were computed prognostically-for historical (1850-2005) and future periods (Representative Concentration Pathway (RCP) 8.5 for 2006-2100) produced by 15 ESMs for the Fifth Phase of the Coupled Model Intercomparison Project (CMIP5). Comparison of ESM prognostic atmospheric CO_2 over the historical period with observations indicated that ESMs, on average, had a small positive bias in predictions of contemporary atmospheric CO_2. Weak ocean carbon uptake in many ESMs contributed to this bias, based on comparisons with observations of ocean and atmospheric anthropogenic carbon inventories. We found a significant linear relationship between contemporary atmospheric CO_2 biases and future CO_2 levels for the multimodel ensemble. We used this relationship to create a contemporary CO_2 tuned model (CCTM) estimate of the atmospheric CO_2 trajectory for the 21st century. The CCTM yielded CO_2 estimates of 600 ± 14 ppm at 2060 and 947 ± 35 ppm at 2100, which were 21 ppm and 32 ppm below the multimodel mean during these two time periods. Using this emergent constraint approach, the likely ranges of future atmospheric CO_2, CO_2-induced radiative forcing, and CO_2-induced temperature increases for the RCP 8.5 scenario were considerably narrowed compared to estimates from the full ESM ensemble. Our analysis provided evidence that much of the model-to-model variation in projected CO_2 during the 21st century was tied to biases that existed during the observational era and that model differences in the representation of concentration-carbon feedbacks and other slowly changing carbon cycle processes appear to be the primary driver of this variability. By improving models to more closely match the long-term time series of CO_2 from Mauna Loa, our analysis suggests that uncertainties in future climate projections can be reduced.
机译：气候变化和未来CO_2浓度之间的反馈强度尚不确定，并且很难使用地球系统模型（ESM）进行预测。我们分析了由排放驱动的模拟，其中大气CO_2的水平是根据历史（1850-2005年）和未来时期（2006年至2100年的代表性浓度途径（RCP）8.5）由耦合后的第五阶段的15个ESM产生的。模型比较项目（CMIP5）。 ESM对历史时期的大气CO_2预后与观测值的比较表明，ESM平均而言对当代大气CO_2的预测具有较小的正偏差。根据与海洋和大气人为碳清单的观察结果的比较，许多ESM中海洋碳吸收较弱导致了这一偏见。我们发现现代大气CO_2偏差与未来多模型集合的CO_2水平之间存在显着的线性关系。我们使用这种关系创建了21世纪大气CO_2轨迹的当代CO_2调谐模型（CCTM）估计。 CCTM得出的CO_2估计值在2060年为600±14 ppm，在2100年为947±35 ppm，在这两个时间段内均比多模型平均值低21 ppm和32 ppm。使用这种紧急约束方法，与整个ESM集合的估计相比，RCP 8.5情景中未来大气CO_2，CO_2引起的辐射强迫和CO_2引起的温度升高的可能范围大大缩小了。我们的分析提供了证据，表明21世纪预计CO_2的许多模型之间的变化与观测时代存在的偏差有关，并且浓度碳反馈和其他缓慢变化的碳循环过程的表示形式存在模型差异。似乎是这种可变性的主要驱动因素。通过改进模型以更紧密地匹配莫纳罗亚火山的CO_2的长期时间序列，我们的分析表明，可以减少未来气候预测中的不确定性。

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