The world could be facing a ‘weak La Niña’ returning within weeks – an ocean cycle that can spell a cooler early winter and wetter spring for Britain.
The World Meteorological Organization (WMO) predicts a 55% chance of La Niña conditions developing between September and November, rising to 60% from October 2024 to February 2025.
El Niño and La Niña, the warm and cool phases of a recurring climate pattern across the tropical Pacific, affect weather and ocean conditions around the world and, broadly speaking, have opposite effects on the world’s climate.
Last year saw the third cooling La Niña event in a row in the Pacific – known as a ‘triple dip’. Last year’s La Niña was linked to disasters including flooding in Australia and drought in the US Southwest.
What is La Niña?
La Niña refers to a cooling event that sees colder ocean surface temperatures coupled with winds and rainfall in the Pacific –which has knock-on effects on weather around the world, including in Britain.
La Niña (which means ‘little girl’ in Spanish) has the opposite impact on weather and global climate as the better-known warming El Niño (‘little boy’), which is the warm phase of the so-called El Niño Southern Oscillation (ENSO).
During La Niña, strong trade winds blow warm water towards the west Pacific causing an upwelling of cool water from the ocean depths in the east Pacific.
This leads to variations in global weather – and the Met Office says it can influence the Atlantic jet stream and our weather here in the UK.
How does La Niña affect weather in the UK?
The Met Office says that La Niña increases the risk of a cold start and mild end to the winter, although the forecaster says that it is just one part of a complex global weather system.
In the later parts of winter, La Niña increases the chance of westerly winds, the Met Office says.
Professor Adam Scaife, the head of long range prediction at the Met Office, said in 2020, “La Niña has a profound effect on weather across the globe with us even seeing impacts that extend across the UK.
“In late autumn and early winter it historically promotes high pressure in the mid-Atlantic, which stops Atlantic weather systems from delivering mild air to the UK, and therefore can allow cold conditions to intensify.
“However, in late winter La Niña can drive a shift of the jet stream towards the poles increasing storminess and heavy rainfall, while bringing milder conditions.”
How does this relate to climate change?
While the effect of La Niña is cooling, it’s occurring against a background of rising temperatures worldwide, the WMO points out.
Between 2020 and 2022, an unusually long La Niña event helped to keep a lid on temperatures worldwide – but this was only temporary.
WMO secretary-general Celeste Saulo said, “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.”