Very early warning of next El Niño

Abstract

The most important driver of climate variability is the El Niño Southern Oscillation, which can trigger disasters in various parts of the globe. Despite its importance, conventional forecasting is still limited to 6 mo ahead. Recently, we developed an approach based on network analysis, which allows projection of an El Niño event about 1 y ahead. Here we show that our method correctly predicted the absence of El Niño events in 2012 and 2013 and now announce that our approach indicated (in September 2013 already) the return of El Niño in late 2014 with a 3-in-4 likelihood. We also discuss the relevance of the next El Niño to the question of global warming and the present hiatus in the global mean surface temperature.

Keywords: ENSO; dynamic networks; spring barrier.

Fig. 1.

The NINO3.4 index and the climate network. The network consists of 14 grid points in the El Niño basin (solid red symbols) and 193 grid points outside this domain (open symbols). The red rectangle denotes the area where the NINO3.4 index is measured. The grid points are considered as the nodes of the climate network that we use here to forecast El Niño events. Each node inside the El Niño basin is linked to each node outside the basin. The nodes are characterized by their surface air temperature (SAT), and the link strength between the nodes is determined from their cross-correlation (see below). The figure is from ref. .

Fig. 2.

The forecasting scheme. (A) We compare the average link strength in the climate network (red curve) with a decision threshold Θ (horizontal line, here ; left scale) and the standard NINO3.4 index (right scale) between January 1981 and November 2013. When the link strength crosses the threshold from below, outside an El Niño episode, we give an alarm and predict that an El Niño episode will start in the following calendar year. The El Niño episodes (when the NINO3.4 index is above 0.5 °C for at least 5 mo) are shown by the solid blue areas. Correct predictions are marked by green arrows and false alarms by dashed arrows. (B) Magnification of A for August (A), September (S), October (O), and November (N) 2013. The figure shows that by September 17 (green arrow), the optimal decision thresholds have been crossed, forecasting an El Nino event in 2014. In A, the learning phase (1950–1980) where the optimal thresholds have been learned has been omitted (31).