The phenomenon known as El Niño, which combined with human-caused warming to supercharge global temperature in 2015/16 and brought chaotic weather worldwide, is officially on its way out. But stepping quickly into El Niño’s shoes is its cooler counterpart, La Niña.

Carbon Brief has been speaking to climate scientists about what it all means. Despite La Niña’s propensity to drag down global temperature, so exceptional is the warming we’ve seen so far this year that 2016 is still likely to top the charts as the hottest year on record.

But we should expect 2017 to be cooler than 2016, as the world begins to feel the full force of La Niña, scientists say.

El Niño is over

TheEl Niñothat left such amarkon weather, crop yields and water supplies in 2015/16 is firmly on its way out.Australia’s Bureau of Meteorologythis weekbecamethe first of the world’s major weather organisations toofficially declare it dead.

The high sea surface temperatures that have characterised the equatorial eastern Pacific Oceanare waningand relative calm is on its way to being restored,say scientists.

This El Niño was no ordinary event.亚当教授Scaife, head of monthly to decadal prediction at the UK’s Met Office, tells Carbon Brief:

The departingElNiño rivalled the massive 1997/8 event as the strongest on record and it was unexpectedly tenacious, saysProf Kim Cobb, whose work at Georgia Tech University involves reconstructing past temperatures in the tropical Pacific using corals. Cobb tells Carbon Brief:

The El Niño is now dissipating at quite a pace. This part of its behaviour is not so unusual, saysProf Mat Collins在气候变化,联合办公椅at the University of Exeter. He tells Carbon Brief:

So, what happens next?

‘Switcheroo’

While the record-topping ElNiñomay be fading fast, hot on its heels is itscooler counterpart, known asLa Niña.

During LaNiña, a change in the trade winds mean more heat is absorbed from the atmosphere into the ocean than usual. In ElNiñoyears, the reverse happens and more heat enters the atmosphere from the ocean instead. This major reshuffling of heat means bothEl Niñoand LaNiñatend to have big – but opposite – effects on global surface temperature.

Most climate modelspredicta return to neutral conditions during 2016’s Northern Hemisphere summer, before tipping the balance the other way into a full-blown LaNiña.

的机会of a LaNiñadeveloping before the end of the northern hemisphere winter is 75%, according to scientists at the US National Oceanic and Atmospheric Administration (NOAA).

How unusual is it to slide straight into a LaNiñaevent after an ElNiño?

Not at all unusual,saysDr Michael McPhaden,a senior expert in the ocean’s role in climate at the NOAA/Pacific Marine Environmental Laboratory in Seattle, US. He tells Carbon Brief:

You can find more information aboutLa Niña on NOAA’s blog, written and maintained by its scientists.In the latest May 2016 update, entitled “Switcheroo!”,Dr Emily Beckersays:

So, what impact will an impending La Niña have on global temperature in 2016?

A record hot start to 2016

So far in 2016, global temperatures have been exceptionally high.

With February, March and April allbreakingmonthly temperature records by the biggest margins ever recorded, 2016 is looking like a sensible bet for the warmest year on record.

Earlier this month,Dr Gavin Schmidt, director of the NASA Goddard Institute for Space Science, put the chance of 2016 topping the temperature rankings at more than 99%.

Will the comingLa Niña alter that picture?

With Apr update, 2016 still > 99% likely to be a new record (assuming historical ytd/ann patterns valid).pic.twitter.com/GTN9sPL2D7

— Gavin Schmidt (@ClimateOfGavin)May 14, 2016

‘A done deal’

Such is the warming seen so far this year that 2016 is likely to retain the top spot, whether or not a LaNiñadevelops, says Cobb. She tells Carbon Brief:

One, is that LaNiñatends to have a smaller influence on global temperature than her warmer brother. A large event still wouldn’t be enough to redress the balance, Cobb says:

Two, is that LaNiñatypically doesn’t reach a peak until winter, or early the following year. This means the biggest impact on global temperature is likely to come in 2017, not in 2016.

That means that, while LaNiñawill reduce some of the warmth in the latter part of 2016,it is likely that 2016 will stay in top spot. Scaife predicts:

Other scientists appear a little less keen to call it just yet. McPhaden tells Carbon Brief:

Collins suggests it would be unwise to rule out the possibility that 2016 could slip down the rankings. He tells Carbon Brief:

How likely is it that the coming LaNiñawill turn out to be a big one?

Waiting game

Looking back over past events can help shed some light on this question. The best analogy is the last big ElNiñoevent in 1997/98, says Cobb, which was followed by a strong LaNiña.

But while the 1997/8 ElNiñowas on a par in terms of magnitude, the event now on its way out had some slightly different characteristics. So that analogy can only take us so far, says Cobb:

Scaife says it’s still a little early to be confident of the strength of LaNiña. But, he adds:

Predicting anything about ElNiñoor LaNiñaat this time of year is notoriously difficult because so much can still change, warns Collins. He tells Carbon Brief:

Prepare for a cooler 2017

If a LaNiña does materialise, it’s reasonable to expect global temperature in 2017 to drop compared to what we’re seeing now, says Cobb. She tells Carbon Brief:

Scaife agrees with this prediction, telling Carbon Brief:

On that point of the background warming, it’s worth noting that as the baseline is pushed ever higher, the distinction between typically hot ElNiñoyears and typically cool LaNiñayears is blurring. The Met Office’sDr Mark McCarthytells Carbon Brief:

McCarthy points to the LaNiñain 1999, which followed the large ElNiñoof 1997-98. That LaNiñawas still warmer than most preceding years, with the exception of 97/98. He ponders:

‘Double jeopardy’

If and when a LaNiñadoes appear later this year, its passage is likely to be accompanied by some very extreme weather.Scaife tells Carbon Brief:

Many of the impacts will simply be the opposite of El Niño, says McPhaden. India, Indonesia and other regions that experienced severe drought during the recent El Niño may see flooding during the La Niña. He tells Carbon Brief:

The good news, relatively-speaking, is that scientists’ ability to predict El Niño and La Niña means we can at least prepare for some of the most damaging impacts, says McCarthy.

La Niña could bring welcome respite in some parts of the world, Cobb says:

Potentially, La Niña could even reverse the recent fortunes of the world’s coral reefs,strickenby rising temperatures and widespread bleaching. Cobb tells Carbon Brief:

For some reef systems, it may be too little too late, Cobb says. But for others, it could mean the difference between life and death.

Carbon Brief will be updating you with the latest on La Niña in the coming months. You can also track its official status on the NOAApages, or via the Met Officeforecasts.

Main image: Monsoon rainclouds over mountains in India. Credit: Gaurav Kavathekar/Flickr.