Fact check: What are El Niño and La Niña and could they impact the climate in 2025?

The past year is certain to be the hottest on record, according to European scientists, and the first to see average global temperatures surpass the Paris Agreement target of 1.5 degrees Celsius above the pre-industrial period.

Soaring temperatures in 2024 were partly boosted by climate conditions known as El Niño (Spanish for "the boy"), according to the World Meteorological Organisation’s data analysis.

In 2025, another phenomenon known as La Niña (Spanish for "the girl") could emerge to slightly cool global temperatures, meaning it looks unlikely that the 2024 temperature record will be broken next year.

But despite this, 2025 is still likely to be among the three hottest years on record, according to the UK’s weather and climate agency, the Met Office.

What are El Niño and La Niña?

El Niño and La Niña are two opposing climate conditions in the Pacific Ocean that affect the weather across the globe.

Trade winds in the Pacific tend to blow from east to west, pushing warm surface waters towards the western Pacific.

El Niño occurs when these winds weaken or reverse, making the waters in the eastern Pacific - off the coast of the Americas - warmer than normal.

In La Niña periods, the east-to-west trade winds become stronger, pushing warm waters further west towards the coasts of Australia and south-east Asia. This causes cold water to ‘upwell’ or rise from the depths of the ocean, making sea surface temperatures cooler on average, particularly in the Americas.

The episodes happen at irregular intervals every two to seven years, and usually last nine to 12 months.

Both El Niño and La Niña can affect weather patterns across the world. Although each episode is different, La Niña is associated with rainier-than-normal conditions in several parts of the world, such as northern Australia, south-eastern Africa and northern Brazil. It can also make flooding more likely in some regions, and cause a more intense hurricane season.

What are scientists predicting for 2025?

The World Meteorological Organisation (WMO) says La Niña conditions could emerge between November 2024 and February 2025.

But its cooling impact on global temperatures could be “weak and short-lived”, the WMO says.

“Since June 2023 we have seen an extended streak of exceptional global land and sea surface temperature. Even if a short-term cooling La Niña event does emerge, it will not change the long-term trajectory of rising global temperatures due to heat-trapping greenhouse gases in the atmosphere,” WMO Secretary-General Celeste Saulo said.

In fact, meteorologists say the temperature forecasts for 2025 are extremely high considering the probability of La Niña conditions.

“Years such as 2025 which aren’t dominated by the warming influence of El Niño, should be cooler. 2016 was an El Niño year and at the time it was the warmest year on record for global temperature. In comparison to our forecast for 2025 though, 2016 is now looking decidedly cool,” according to Professor Adam Scaife, who leads the UK Met Office’s global forecast for 2025.

Paris Agreement not (yet) breached

It looks likely that 2024 temperatures will for the first time exceed 1.5 degrees Celsius above pre-industrial times, a benchmark set by the 2015 Paris Climate Agreement for the first time.

But passing that threshold for one year is not considered a breach of the Paris threshold. Scientists say that the threshold would need to be breached persistently, over a period as long as 20-30 years.

Some scientists say the link between climate change and the phenomena of La Niña and El Niño is not entirely clear.