December 23, 2015 / 9:48 AM / 3 years ago

Don't get too used to El Niño, it's already fading: Braun

(Reuters) - Hidden beyond the current El Niño hype, solid evidence exists that the demise of the record-breaking event has already begun and that all traces of it will have vanished by next August.

The warm sea surface temperature (SST) anomalies in the central-east Pacific Ocean, which characterize El Niño and have been steadily rising since early March, have reached a plateau in recent weeks (tmsnrt.rs/1UXHGTv).

The current El Niño event has been compared to those in 1997/98 and 1982/83, the strongest two events observed since 1950. Last month, SST anomalies surpassed the record-warm monthly values of November 1997.

The 1997/98 and 1982/83 El Niño events began dismantling in almost the exact same way, both during the height of their strength, and the data shows an uncannily similar pattern is already unfolding in 2015.

This certainly marks the beginning of the end for the monster El Niño, and not only are models in agreement that the phenomenon has already reached its peak, several of them strongly indicate that the scenario will be vastly different one year from now.

And the historical data backs that theory near-perfectly.

DEATH OF A GIANT

Several atmospheric and oceanic ingredients work together to support El Niño, but the phenomenon appears virtually unsustainable without two key variables: trade winds in the western equatorial Pacific Ocean and temperature anomalies below the ocean’s surface.

While El Niño is directly defined by activity in the central and eastern Pacific, it cannot be long-lived without support from the entire ocean.

Strongly reversed trade winds in the western basin sustain El Niño by continuing to push anomalously warm pools of water eastward into the Niño region.

But once an ingredient is lost – either the western Pacific trades revert to their normal easterly direction or the ocean waters cool down – the process is disrupted and El Niño’s lifeline is essentially severed.

In both 1982 and 1997, western trade winds were highly reversed but abruptly returned to normal within one month at the end of both years. Although these winds have not been as anomalously strong in 2015, the same rapid jump occurred last month (tmsnrt.rs/1J2iEB1).

One month later in both January 1983 and 1998, temperature anomalies in the upper 300 meters of the equatorial Pacific Ocean took a nose dive and did not return to levels warmer than normal until two years later (tmsnrt.rs/1J2jgXc).

The subsurface Pacific waters are still quite warm at present, similar to “pre-crash” levels in 1982 and 1997, but there are already signs that they could soon take a tumble.

SST anomalies across the equatorial Pacific basin have cooled roughly one-half a degree over the last four weeks. At the same time, a large pool of cold water beneath the surface in the western Pacific has been expanding eastward, nearly doubling in size over the past two months.

HELLO, LA NIÑA?

By July in both 1983 and 1998, SST anomalies in the equatorial Pacific were back near zero or even in negative territory. If the current El Niño in fact meets its demise in the exact fashion as its predecessors, it too will likely be gone by mid-2016.

Current climate models only predict through early autumn 2016, but they have already been indicating a rapid descent from El Niño over the next few months, and historical data suggests the same.

A simple inspection of the years immediately following past strong El Niño years reveals that the chances are very likely for La Niña, classified by cool SST anomalies in the equatorial Pacific, to be present by the close of 2016.

Since 1950, the four strongest El Niño events led to the strongest, seventh-, and eighth-strongest La Niña events on record in the following year. Weak La Niña conditions were observed in the fourth instance.

Consensus among international climate models is that by August, SST anomalies will be near zero, and are likely to keep declining toward the end of 2016 (tmsnrt.rs/1UXILL0).

But in the near term, El Niño will continue to have a big presence. Although models indicate that El Niño likely reached its peak last month, the globe can still expect to be in an El Niño state through the first half of 2016.

Both the rapid descent into La Niña and the event itself have presented problems for North and South America in the past.

The transition period has been associated with several summer droughts in the United States, and key corn and soybean growing areas of Argentina and Southern Brazil tend to be drier than normal during La Niña events.

Additionally, the Northern United States has more frequently observed brutally cold and snowy winters during La Niña events than El Niño ones.

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Graphic: Weekly Sea Surface Temperature Anomalies in the Pacific Ocean tmsnrt.rs/1UXHGTv

Graphic: Mid-December 2015 Plume of Model ENSO Predictions (IRI/CPC) tmsnrt.rs/1UXILL0

Graphic: El Nino, temperature anomalies vs trade winds tmsnrt.rs/1J2iEB1

Graphic: El Nino, surface vs subsurface temperature anomalies in the Pacific Ocean tmsnrt.rs/1J2jgXc

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Reporting by Karen Braun in Chicago; Editing by Matthew Lewis

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