Open AccessDefining El Niño indices in a warming climate
Author(s) -
Geert Jan van Oldenborgh,
Harry H. Hendon,
Tim Stockdale,
Michelle L’Heureux,
Erin Coughlan de Pérez,
Roop Singh,
Maarten van Aalst
Publication year - 2021
Publication title -
environmental research letters
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 2.37
H-Index - 124
ISSN - 1748-9326
DOI - 10.1088/1748-9326/abe9ed
Subject(s) - anomaly (physics) , climatology , environmental science , global warming , sea surface temperature , index (typography) , tropical cyclone , el niño southern oscillation , convection , atmospheric sciences , climate change , meteorology , geology , geography , oceanography , physics , condensed matter physics , world wide web , computer science
Extreme weather and climate events associated with El Niño and La Niña cause massive societal impacts. Therefore, observations and forecasts are used around the world to prepare for such events. However, global warming has caused warm El Niño events to seem bigger than they are, while cold La Niña events seem smaller, in the commonly used Niño3.4 index (sea surface temperature (SST) anomalies over 5 ∘ S–5 ∘ N, 120–170 ∘ W). We propose a simple and elegant adjustment, defining a relative Niño3.4 index as the difference between the original SST anomaly and the anomaly over all tropical oceans (20 ∘ S–20 ∘ N). This relative index describes the onset of convection better, is not contaminated by global warming and can be monitored and forecast in real-time. We show that the relative Niño3.4 index is better in line with effects on rainfall and would be more useful for preparedness for El Niño and La Niña in a changing climate and for El Niño—Southern Oscillation research.