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How Much Global Cooling Will We See On Transition To La Niña?

Karen Braun, Reuters

The potential for the massive El Niño to transition into La Niña later in the year is one of the hottest topics in commodities markets right now.

These fluctuations of sea surface temperatures in the tropical Pacific Ocean can have drastically different impacts on global weather depending on which phase is present – El Niño, the warm phase, or La Niña, the cool phase. They are one of the few clues to seasonal weather patterns several months or even years in advance.

The short question-and-answer session would look like this: Are we headed for La Niña toward the end of 2016? Looks that way. Will it be a big one? Not sure.

The answers may help dictate whether drought is likely in South America, winter will be cold in the United States or abundant rains will return to Southeast Asia, among other things.

Although strength is yet to be determined, the progression of certain atmospheric and oceanic variables will provide clues on the possible entry to La Niña. Particular insight will be offered by the timing of these events, as it might be the difference between strong La Niña and nothing at all.

It seems unlikely that we will stay in El Niño, though. Of the 14 El Niño events since 1950, excluding this year, only one of them remained El Niño into the following year, while three others lingered in neutral to weak El Niño territory. So the odds favor La Niña, but in meteorology, odds alone are not enough.

A La Niña environment has already begun to develop. Cooler waters are building beneath the surface in the Pacific Ocean and El Niño-supporting trade winds have lessened. But sea surface temperatures, or SSTs, in the defining region of the Pacific remain very warm, so we are still amid a strong El Niño event.

It is helpful to look for historical instances in which El Niño turned into La Niña through the course of a year. This has occurred only a handful of times since 1982, but there are enough similarities among these analogs that we can use them to inform this year’s likely outcome.

Selected analog years suggest that huge dropoffs of SST anomalies into negative, La Niña-defining territory are likely to take place between April and July. These analogs also suggest that when the SST anomalies cross into negative territory later than June, a weaker La Niña event is likely to follow (

Although the journey to La Niña has already begun, there are still some variables that need to fall into place in order to lock in this forecast solidly for the end of 2016.

Checked Boxes

El Niño decay is unlikely to proceed without the shutdown of its two key mechanisms: strongly reversed trade winds in the western Pacific Ocean and net warmth below the ocean’s surface. Check, and check.

One of the first anti-El Niño signals was the abrupt strengthening of western Pacific trade winds back to near-normal levels last November. It is probably no mistake then that El Niño reached maximum strength that month

But this has not weakened El Niño as much as it would seem. Localized but strong westerly bursts of wind over the central and eastern Pacific – the Niño region – have propped up SSTs in recent weeks, though the wind bursts have been less frequent since early March.

Enter the ocean temperature anomalies. Water temperatures just below the surface across the entire Pacific Ocean have turned net cool, and this massive, cold blob is now lurking below the surface waiting for its chance to turn up. The colder the anomaly becomes, the bigger the potential for La Niña becomes

The cold blob can surface in the Niño region with the help of the trade winds. The winds must continue to strengthen, and the pace at which they do so will determine just how soon we might enter La Niña.

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