Department of Geosciences, University of Arizona, Tucson, AZ, USA.
Department of Atmospheric and Oceanic Sciences, University of Colorado Boulder, Boulder, CO, USA.
Nature. 2024 Oct;634(8033):374-380. doi: 10.1038/s41586-024-07984-y. Epub 2024 Sep 25.
El Niño events, the warm phase of the El Niño-Southern Oscillation (ENSO) phenomenon, amplify climate variability throughout the world. Uncertain climate model predictions limit our ability to assess whether these climatic events could become more extreme under anthropogenic greenhouse warming. Palaeoclimate records provide estimates of past changes, but it is unclear if they can constrain mechanisms underlying future predictions. Here we uncover a mechanism using numerical simulations that drives consistent changes in response to past and future forcings, allowing model validation against palaeoclimate data. The simulated mechanism is consistent with the dynamics of observed extreme El Niño events, which develop when western Pacific warm pool waters expand rapidly eastwards because of strongly coupled ocean currents and winds. These coupled interactions weaken under glacial conditions because of a deeper mixed layer driven by a stronger Walker circulation. The resulting decrease in ENSO variability and extreme El Niño occurrence is supported by a series of tropical Pacific palaeoceanographic records showing reduced glacial temperature variability within key ENSO-sensitive oceanic regions, including new data from the central equatorial Pacific. The model-data agreement on past variability, together with the consistent mechanism across climatic states, supports the prediction of a shallower mixed layer and weaker Walker circulation driving more frequent extreme El Niño genesis under greenhouse warming.
厄尔尼诺事件是厄尔尼诺-南方涛动（ENSO）现象的暖相位，会放大全球气候的可变性。气候模型预测的不确定性限制了我们评估这些气候事件在人为温室变暖下是否会变得更加极端的能力。古气候记录提供了过去变化的估计，但尚不清楚它们是否可以约束未来预测的潜在机制。在这里，我们使用数值模拟揭示了一种机制，该机制可以对过去和未来的强迫做出一致的响应变化，从而允许模型根据古气候数据进行验证。模拟的机制与观测到的极端厄尔尼诺事件的动态一致，这些事件是由于强烈耦合的海洋流和风导致西太平洋暖池迅速向东扩张而发展起来的。在冰川条件下，由于更强的沃克环流驱动的混合层变深，这些耦合相互作用会减弱。一系列热带太平洋古海洋学记录表明，包括来自中赤道太平洋的新数据，关键的厄尔尼诺敏感海洋区域的冰川温度变化减少，这支持了 ENSO 可变性和极端厄尔尼诺发生频率降低的假说。模型与数据在过去变异性上的一致性，以及在气候状态下的一致机制，支持了在温室变暖下，混合层变浅和沃克环流减弱，从而导致更频繁的极端厄尔尼诺形成的预测。
