| 英文摘要: | El Niño events are a prominent feature of climate variability with global climatic impacts. The 1997/98 episode, often referred to as ‘the climate event of the twentieth century’1, 2, and the 1982/83 extreme El Niño3, featured a pronounced eastward extension of the west Pacific warm pool and development of atmospheric convection, and hence a huge rainfall increase, in the usually cold and dry equatorial eastern Pacific. Such a massive reorganization of atmospheric convection, which we define as an extreme El Niño, severely disrupted global weather patterns, affecting ecosystems4, 5, agriculture6, tropical cyclones, drought, bushfires, floods and other extreme weather events worldwide3, 7, 8, 9. Potential future changes in such extreme El Niño occurrences could have profound socio-economic consequences. Here we present climate modelling evidence for a doubling in the occurrences in the future in response to greenhouse warming. We estimate the change by aggregating results from climate models in the Coupled Model Intercomparison Project phases 3 (CMIP3; ref. 10) and 5 (CMIP5; ref. 11) multi-model databases, and a perturbed physics ensemble12. The increased frequency arises from a projected surface warming over the eastern equatorial Pacific that occurs faster than in the surrounding ocean waters13, 14, facilitating more occurrences of atmospheric convection in the eastern equatorial region. The 1982/83 and 1997/98 extreme El Niño events were characterized by an exceptional warming, with sea surface temperatures (SSTs) exceeding 28 °C extending into the eastern equatorial Pacific2, 3. This led to an equatorward shift of the intertropical convergence zone (ITCZ), and hence intense rainfall in the equatorial eastern Pacific where cold and dry conditions normally prevail. This major reorganization of atmospheric convection severely disrupted global weather patterns and spurred major natural disasters. Catastrophic floods occurred in the eastern equatorial region of Ecuador and northern Peru3, 7, and neighbouring regions to the south and north experienced severe droughts (Supplementary Fig. 1). The anomalous conditions caused widespread environmental disruptions, including the disappearance of marine life and decimation of the native bird population in the Galapagos Islands15, 16, and severe bleaching of corals in the Pacific and beyond4, 5. The impacts extended to every continent, and the 1997/98 event alone caused US$35–45 billion in damage and claimed an estimated 23,000 human lives worldwide17. The devastating impacts demand an examination of whether greenhouse warming will alter the frequency of such extreme El Niño events. Although many studies have examined the effects of a projected warming on the Pacific mean state, El Niño diversity and El Niño teleconnections18, 19, 20, 21, the issue of how extreme El Niños will change has not been investigated. Here we show that greenhouse warming leads to a significant increase in the frequency of such events. We contrast the characteristics between the extreme and moderate El Niño events using available data sets22, 23, focusing on December–January–February (DJF), the season in which El Niño events peak. During moderate events, which include canonical and Modoki El Niño24, the eastern boundary of the warm pool (indicated by the 28 °C isotherm, purple, Fig. 1a) and the atmospheric convective zone move eastwards to just east of the Date Line. The ITCZ lies north of the Equator25, and the rainfall anomaly over the eastern equatorial Pacific is small (Fig. 1a).
| http://www.nature.com/nclimate/journal/v4/n2/full/nclimate2100.html
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