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Earth System Models Are Not Capturing Present-Day Tropical Forest Carbon Dynamics
Earth's Future ( IF 8.852 ) Pub Date : 2021-05-05 , DOI: 10.1029/2020ef001874
Alexander Koch 1 , Wannes Hubau 2, 3 , Simon L. Lewis 4, 5
Affiliation  

Tropical forests play a key role in absorbing carbon from the atmosphere into the land surface. Recent analyses of long-term (1985–2014) forest inventory plots across the tropics show that structurally intact tropical forest are a large carbon sink, but that this sink has saturated and is projected to be in long-term decline. Here we compare these results with estimates from the two latest generations of Earth System Models, Climate Modelling Intercomparison Project 5 (CMIP5) (19 models) and CMIP6 (17 models). While CMIP5 and CMIP6 are of similar skill, they do not reproduce the observed 1985–2014 carbon dynamics. The “natural” pan-tropical carbon sink from inventory data is 0.99 Pg C yr−1 (95% CI 0.7–1.3, n = 614) between 2000 and 2010, the best sampled decade, double the CMIP6 multimodel-mean of 0.45 Pg C yr−1 (95% CI 0.35–0.55). The observed saturating and declining sink is not captured by the models, which show modest increases in sink strength. The future (2015–2040) “natural” pan-tropical sink from a statistical model driven by extrapolating past trends of its putative environmental drivers decreases by 0.23 Pg C per decade (95% CI 0.09–0.39) until the 2030s, while the CMIP6 multimodel-mean under the climate change scenario closest to the statistical model project an increasing carbon sink (0.54 Pg C per decade; 95% CI 0.25–0.67). CMIP multimodel-means reproduce the response of carbon gains from tree growth to environmental drivers, but the modeling of carbon losses from tree mortality does not correspond well to the inventory data. The model-observation differences primarily result from the treatment of mortality in models.

中文翻译:

地球系统模型无法捕捉当今的热带森林碳动态

热带森林在吸收大气中的碳到土地表面中起着关键作用。对热带地区长期(1985-2014年)森林资源清单的最新分析表明,结构完整的热带森林是一个大的碳汇,但该汇已经饱和,并且预计将长期下降。在这里,我们将这些结果与两个最新一代地球系统模型(气候模型比对项目5(CMIP5)(19个模型)和CMIP6(17个模型))的估计值进行比较。尽管CMIP5和CMIP6具有相似的技能,但它们没有重现1985-2014年观察到的碳动态。来自库存数据的“自然”泛热带碳汇为0.99 Pg C yr -1(95%CI 0.7–1.3,n = 614)在2000年至2010年之间,这是采样率最高的十年,是CMIP6多模型平均值的两倍,即0.45 Pg C yr -1(95%CI 0.35-0.55)。模型未捕获观察到的饱和和下降沉,表明沉强度有所增加。统计模型推论的未来(2015–2040)“自然”泛热带沉没,推定其过去的环境驱动因素的过去趋势,直到2030年代每十年减少0.23 Pg C(95%CI 0.09–0.39),而CMIP6在最接近统计模型的气候变化情景下,多模型均值表明碳汇增加(每十年0.54 Pg C; 95%CI 0.25–0.67)。CMIP多模型方法重现了树木生长过程中碳增加对环境驱动因素的响应,但是树木死亡率造成的碳损失建模与库存数据并不十分吻合。模型观察差异主要是由模型中的死亡率处理引起的。
更新日期:2021-05-22
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