Historical change of El Nino properties sheds light on future changes of extreme El Nino
Historical change of El Nino properties sheds light on future changes of extreme El Nino
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DOI：
10.1073/pnas.1911130116
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发表时间：
2019-11-05
影响因子：
11.1
通讯作者：
Liu, Jian
中科院分区：
文献类型：
--
作者：
Wang, Bin;Luo, Xiao;Liu, Jian
人为变暖导致的厄尔尼诺现象强度变化对社会具有重要意义，但目前气候模型的预测在很大程度上仍然不确定。目前厄尔尼诺的分类并没有区分强厄尔尼诺事件和中度厄尔尼诺事件，因此很难预测厄尔尼诺事件未来强度的变化。本文通过对厄尔尼诺事件的爆发和放大过程进行聚类分析，对1901年至2017年的33次厄尔尼诺事件进行分类，并由此将厄尔尼诺事件分为强厄尔尼诺事件和中度厄尔尼诺事件以及厄尔尼诺事件的爆发事件和连续事件。厄尔尼诺爆发的三类表现出不同的发展机制。我们发现，自20世纪70年代以来，厄尔尼诺现象的发生方式已经从东太平洋起源转向西太平洋起源，极端事件的发生更加频繁。据推测，这种状况的变化是由于西太平洋背景变暖以及赤道中太平洋纬向和垂直海面温度（SST）梯度的增加引起的，这揭示了一个可能导致未来极端厄尔尼诺事件增加的控制因素。耦合模型比对项目第五阶段（CMIP5）模型的预测表明，如果预测的中太平洋纬向海温梯度增强，强厄尔尼诺事件的频率和强度都将显着增加。如果目前观察到的背景变化在未来的人为强迫下持续下去，预计会出现更频繁的强厄尔尼诺事件。然而，模型预测的赤道纬向海温梯度的不确定性仍然是准确预测厄尔尼诺未来变化的主要障碍。
El Nino's intensity change under anthropogenic warming is of great importance to society, yet current climate models' projections remain largely uncertain. The current classification of El Nino does not distinguish the strong from the moderate El Nino events, making it difficult to project future change of El Nino's intensity. Here we classify 33 El Nino events from 1901 to 2017 by cluster analysis of the onset and amplification processes, and the resultant 4 types of El Nino distinguish the strong from the moderate events and the onset from successive events. The 3 categories of El Nino onset exhibit distinct development mechanisms. We find El Nino onset regime has changed from eastern Pacific origin to western Pacific origin with more frequent occurrence of extreme events since the 1970s. This regime change is hypothesized to arise from a background warming in the western Pacific and the associated increased zonal and vertical sea-surface temperature (SST) gradients in the equatorial central Pacific, which reveals a controlling factor that could lead to increased extreme El Nino events in the future. The Coupled Model Intercomparison Project phase 5 (CMIP5) models' projections demonstrate that both the frequency and intensity of the strong El Nino events will increase significantly if the projected central Pacific zonal SST gradients become enhanced. If the currently observed background changes continue under future anthropogenic forcing, more frequent strong El Nino events are anticipated. The models' uncertainty in the projected equatorial zonal SST gradients, however, remains a major roadblock for faithful prediction of El Nino's future changes.