| 英文摘要: | Computer models and theory do not offer a consensus on how El Niño will change under global warming. Despite this disagreement, a study indicates a robust increase in the frequency of extreme El Niño episodes. About once every four years, on average, one of the most powerful and far-reaching climate phenomena, known as El Niño, extends its influence to most continents and oceans of the world. This phenomenon, which originates in the tropics and is characterized by unusually warm and wet conditions in the equatorial eastern Pacific Ocean, triggers large-scale weather patterns that disrupt remote regions through floods, droughts, heat waves and cold spells. During extreme El Niño episodes, as occurred in 1982/83 and 1997/98, the worldwide societal, economic and environmental impacts have been particularly costly, with damages totalling in the tens of billions of US dollars and thousands of lives lost1. Although the physical mechanisms and effects of El Niño in today's climate are relatively well understood, there is considerable uncertainty regarding how the El Niño phenomenon will respond to global warming2. Even in the face of this uncertainty, in this issue of Nature Climate Change Cai and colleagues3 identify and report on a robust change in climate models — extreme El Niño episodes will increase in frequency under global warming. Usually, during austral summer, which is the peak season of El Niño, conditions in the equatorial eastern Pacific Ocean region are very dry and relatively cool and most tropical ocean rainfall is confined to the warmer western Indo-Pacific region (Fig. 1a). During typical El Niño episodes, the eastern Pacific Ocean warms considerably and tropical rainfall shifts towards the equatorial central Pacific, but the equatorial eastern Pacific stays dry because the atmosphere remains stable. However, more dramatic eastern Pacific warming during extreme El Niño episodes disrupts the eastern Pacific sea surface temperature gradients, breaks the stability barrier and triggers enormous increases in deep showers and thunderstorms (Fig. 1b). This atmospheric convection, manifesting as heavy rainfall, is the primary driver of El Niño-related extreme weather in remote regions. Cai and colleagues focus on the mechanism by which global warming may impact the occurrence of extreme eastern Pacific rainfall events during these rare El Niño episodes. Although there is considerable uncertainty regarding how the sea surface temperature variability may change, the authors find a more robust link with extreme rainfall, which is tied to the pattern of equatorial Pacific sea surface warming.
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