The La Niña weather phenomenon is expected to arrive later this year and bring cooler temperatures, after the heat records fueled by El Niño and broken month after month for the past year.
“The El Niño phenomenon in 2023 and 2024, which helped fuel a rise in global temperatures and extreme weather conditions around the world, is showing signs that it is coming to an end. There will likely be a return to La Niña later this year”, indicates the World Meteorological Organization (WMO), the UN institution, in its latest bulletin dedicated to these two natural meteorological phenomena which have almost opposite impacts.
La Niña refers to the large-scale cooling of ocean surface temperatures in the central and eastern equatorial Pacific. It is associated with changes in tropical atmospheric circulation: winds, pressure and precipitation. However, the precise effects vary depending on the intensity, the duration but also the time of year at which the phenomenon occurs and the interaction with other climatic phenomena, underlines the WMO.
A rise in average global temperatures
In contrast, El Niño is a phenomenon that causes an increase in average global temperatures, due to warming of water in the central and eastern tropical Pacific Ocean, which influences precipitation, winds and ocean currents . It occurs every two years at age seven and generally lasts nine to twelve months.
The latest El Niño, which began in June 2023, ranks among the five most intense ever measured, according to the World Meteorological Organization (WMO). While it should therefore be coming to an end, La Niña could well succeed it. According to the WMO, there is a 60% chance that the climatic phenomenon will appear during the July-September period. These probabilities increase to 70% in August-November, according to the UN agency, which judges that “the risk of a reappearance of El Niño is negligible during this period”.
Before then, over the June-August period, the organization estimates that there is an equal chance (50%) of conditions being neutral – neither Niño nor Niña – or of a transition to La Niña.
No pause in long-term climate change
These natural phenomena are obviously not the only causes of climate change. These events “are now occurring in the context of human-induced climate change, which is increasing global temperatures, exacerbating extreme weather and climate conditions and impacting seasonal patterns of precipitation and temperatures”, recalls the ‘OMM.
Every month since June 2023 has set a new temperature record – and 2023 has been by far the hottest year on record. “The end of El Niño does not mean a pause in long-term climate change, as our planet will continue to warm due to heat-trapping greenhouse gases. Exceptionally high sea surface temperatures will continue to play an important role in the coming months,” said Ko Barrett, Deputy Secretary-General of WMO, quoted in the press release.
Thus La Niña is already incorporated into the forecasts of the National Oceanic and Atmospheric Administration (NOAA) for the 2024 hurricane season in the North Atlantic, which is due to begin in early June. It promises to be “extraordinary”, with four to seven Category 3 or higher hurricanes possible, according to NOAA.
The WMO also recalls that the last nine years have been the hottest on record, despite the cooling effect of a long “La Niña”, which lasted from 2020 to early 2023. As for El Niño, it peaked in December 2023 and is one of the five strongest on record.
“Our weather conditions will continue to be more extreme due to the additional heat and humidity in our atmosphere,” Ko Barrett further emphasizes. “This is why the Early Warning for All initiative remains WMO’s top priority,” recalled the official. The organization has made it a priority to ensure that the entire world population is covered by early warning systems for weather risks by the end of 2027 and in particular the most deprived areas as in Africa.