The warming El Niño weather phenomenon could form later this year, potentially pushing global temperatures to record heights.

There is a 50-60% chance of El Niño developing during the July-September period and beyond, according to the US National Oceanic and Atmospheric Administration.

The World Meteorological Organization will issue an update on El Niño on Tuesday.

Here's what you need to know about El Niño and its cooler sister, La Niña.

El Niño and its cooler sister La Niña are two phases of a natural climate pattern across the tropical Pacific known as the El Niño-Southern Oscillation (ENSO).

Peruvian and Ecuadorian fishermen coined the term El Niño ("the boy" or "the Christ Child") in the 19th century for the arrival of an unusually warm ocean current off the coast that reduced their catch just before Christmas.

Scientists chose the name La Niña as the opposite of El Niño. Between the two events, there is a "neutral" phase.

El Niño can weaken consistent trade winds that blow east to west across the tropical Pacific, influencing weather by affecting the movement of warm water across this vast ocean.

This weakening warms the usually cooler central and eastern sides of the ocean, altering rainfall over the equatorial Pacific and wind patterns around the world.

The extra heat at the surface of the Pacific releases energy into the atmosphere that can temporarily drive up global temperatures, which is why El Niño years are often among the warmest on record.

"All else being equal, a typical El Niño event tends to cause a temporary increase in the global mean temperature on the order of 0.1C-0.2C," Nat Johnson, an NOAA meteorologist, told AFP.

El  Niño occurs every two to seven years.

It typically results in drier conditions across southeast Asia, Australia, southern Africa, and northern Brazil, and wetter conditions in the Horn of Africa, the southern US, Peru, and Ecuador.

The last El Niño occurred in 2023-2024, contributing to making 2023 the second highest year on record and 2024 the all-time high.

Carlo Buontempo, director of the European Union's Copernicus Climate Change Service, told AFP in January that 2026 could be "another record-breaking year" if El Niño appears this year.

However, El Niño's impact would be higher in 2027 than in 2026 if it develops in the second half of this year, said Tido Semmler, a climate scientist at Ireland's National Meteorological Service.

"It takes time for the global atmosphere to react to the El Niño," he said.

"Having said this, there is a risk of 2026 being the warmest year on record even without El Niño, due to the global warming trend," Semmler told AFP.

"2027 would face an increased risk of getting a record warm year if El Niño developed in the second half of 2026," he added.

The latest La Niña episode was relatively weak and short lived, starting in December 2024 and due to enter a neutral phase during the February-April period.

La Niña cools the eastern Pacific Ocean for a period of about one to three years, generating the opposite effects to El Niño on global weather.

It leads to wetter conditions in parts of Australia, southeast Asia, India, southeast Africa, and northern Brazil, while causing drier conditions in parts of South America.

La Niña did not stop 2025 from being the third hottest on record.

The NOAA adopted in February a new way of determining El Niño and La Niña events.

The old Oceanic Niño Index (ONI) compared the three-month average sea surface temperature one region of the Pacific with a 30-year average in the same area.

But as the oceans have been warming rapidly, that old 30-year average can be out of date.

The new method, the Relative Oceanic Niño Index (RONI), compares how warm or cool the east-central Pacific is compared to the rest of the tropics.

The NOAA said RONI is a "clearer, more reliable way" to track El Niño and La Niña in real time.