How will this year’s record-breaking El Niño affect NZ and the world? 5 things to know

Kevin Carter/Getty Images Months out from its projected peak, El Niño is already helping push ocean temperatures into record territory.

July brought the highest global sea-surface temperatures ever recorded for that month, partly fuelled by the fast-developing climate pattern.

The latest forecasts suggest there is much more to come.

So, what exactly is El Niño, why is this one potentially so significant and what could it mean for New Zealand? Here are five things to know.

El Niño begins with a huge shift in ocean heat El Niño is a natural climate pattern involving unusual warming of the central and eastern tropical Pacific Ocean, accompanied by changes in winds and atmospheric circulation.

Here’s how the process normally works.

The sun heats the tropical ocean, while trade winds push warm surface water westward across the equatorial Pacific, causing it to pile up around Indonesia, northern Australia and Southeast Asia.

Cooler water rises from below in the eastern Pacific.

This build-up means sea levels in the western Pacific “Warm Pool” average about 60cm higher than in the eastern Pacific off South America.

Without the trade winds holding it there, that warm water would flow back eastwards.

But there is a limit to how much can build up.

Exactly how an El Niño gets underway varies, with weather and tropical storms sometimes weakening the tradewinds and providing the trigger.

Once it begins, warm water starts surging back eastwards across the Pacific.

It can take two to three months to cross the ocean, shifting thunderstorms and rainfall as it goes and influencing weather patterns far beyond the tropical Pacific.