Scientists say there is a high likelihood of El Nino conditions developing over the Northern Hemisphere summer, with some forecasts pointing to a potentially record-breaking event.

El Nino is a natural climate phenomenon that warms surface temperatures in the central and eastern equatorial Pacific Ocean, bringing worldwide changes in winds, rainfall patterns and erratic weather.

Copernicus said its June outlook "further strengthens the likelihood of a large El Nino event".

"The odds are strongly in favour of a moderate to strong, or probably strong to record-breaking, event at this stage," the service's director Carlo Buontempo told AFP.

Its outlook combines El Nino predictions from nine of the world's leading meteorological centres -- including in Europe, the United States, Australia and Japan -- into a single forecast.

Some 75 percent of these models predict average sea temperatures in key El Nino zones in the Pacific could surge 2.5C or more by November -- exceptionally high projections.

Last month, confidence was just 50 percent.

"From May 1st to June 1st all models effectively shifted upward their predictions," said Buontempo, a climate scientist. The median forecast was just above 3C in November, he said.

This would be well above what is dubbed "super" El Nino territory and rank among the most powerful ever recorded.

Just three events -- 1982/83, 1997/98 and 2015/16 -- have breached 2C since the first major El Nino recorded in the modern era in 1877/78.

- Strong signal -

Copernicus stressed that "individual models are not unanimous in the support for a very strong event" but those at the lower end had historically underestimated El Nino strength.

Scientists say that observations in the real world also point to an unusual event taking shape.

Sea temperatures in key El Nino zones of the equatorial Pacific are rapidly rising and an enormous pool of abnormally warm water is massing beneath the surface.

El Ninos build strength as the ocean and atmosphere increasingly "couple" over the summer months, shifting air pressure, cloud patterns and winds.

This feedback loop can turn a modest El Nino into a blockbuster event, supercharging heat and triggering chaotic weather worldwide.

El Nino tends to peak late in the year but heat in the oceans releases more slowly into the atmosphere, pushing up global temperatures the following year.

Climate scientists interviewed by AFP said 2027 would likely surpass 2024 as the hottest year on record.

Scientists say that every El Nino is different, but major events often follow familiar patterns.

This includes drought across parts of the Amazon, Indonesia and Australia, disrupted monsoons in India, and shifting rainfall throughout the tropics.

Scientists stress that stronger El Ninos raise the odds of more severe impacts -- but do not guarantee them.

Long-range forecasts carry significant uncertainty and their reliability generally improves as the period being predicted draws closer.