NOAA’s Oceanic Niño Index (ONI) is used to record for historical purposes the occurrence and duration of El Niño episodes, based on the monitoring of sea surface temperatures (SSTs) in the central Pacific Ocean. The ONI is used to identify the onset of an above average SST threshold that persists for several months, encompassing both the beginning and end of an El Niño episode. The first appearance of an anomalous seasonal value of 0.5 °C suggests with a high probability that an El Niño could emerge, but for heightened warnings, one must wait for several months. In this article, we proposed that the ONI value of 0.7 °C identifies a tipping point at which the El Niño event becomes locked in, which can provide additional lead time for mitigative actions to be taken by societal decision makers. Our preliminary findings suggest that a first appearance of 0.7 °C value could serve as a credible marker of El Niño’s locked-in phase, which can provide additional credibility to the current 0.5 °C El Niño onset indicator for at-risk societies to get ready for El Niño’s foreseeable societal and ecological impacts.

中文翻译：

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审查海洋Niño指数（ONI），以增强社会应对厄尔尼诺现象的准备

基于对太平洋中部海表温度（SST）的监视，NOAA的海洋Niño指数（ONI）用于记录历史厄尔尼诺事件的发生和持续时间。ONI用于识别持续数月的SST高于平均阈值的发作，包括厄尔尼诺事件的开始和结束。最初出现的季节性异常值为0.5°C，很有可能会出现厄尔尼诺现象，但对于高度警告，必须等待几个月。在本文中，我们提出ONI值为0.7°C可以确定ElNiño事件被锁定的临界点，这可以为社会决策者采取缓解措施提供额外的时间。