Is this year’s El Niño set to be an especially strong one?
Questions and answers about the climate phenomenon and its consequences
How do El Niño and La Niña develop, and what happens during these events?
El Niño is a natural climate phenomenon in which surface waters in the central and eastern Pacific warm up unusually strongly. El Niño occurs every two to seven years towards the end of the year, hence the name El Niño, which is Spanish for 'Christ child'.
El Niño is triggered when the trade winds blowing from east to west across the Pacific are weakened, for example by tropical storms. Under normal conditions, trade winds push warm Pacific surface water to the west. In the east, off the coast of Peru, cold, nutrient-rich water rises from the depths to the surface, sustaining abundant fish stocks there. When the trade winds weaken, warm water accumulates at the surface off the west coast of South America. When this water is more than 0.5 °C warmer than usual, meteorologists speak of an El Niño. In the process, the warm water can also spread from the tropics into the subtropics.
El Niño is part of the El Niño–Southern Oscillation (ENSO), whose counterpart is La Niña. During La Niña, trade winds intensify: warm water is driven further into the western Pacific, allowing more cold water to rise to the surface along the west coast of South America. When surface water is more than 0.5 °C colder than usual, it is classified as La Niña.
El Niño and La Niña
What are the regional and global consequences of El Niño – climatic, health-related, ecological, and economic?
For every degree that the sea surface temperature off the west coast of South America rises, the global average temperature increases by 0.1 °C. El Niño and La Niña affect the weather in different regions in very distinct ways. The impacts are particularly severe in South America as well as in Indonesia and Australia. The most serious impacts of an El Niño include:
- Extremely heavy rainfall along the west coast of South America, which can lead to flooding resulting in numerous casualties and extensive damage.
- A lack of cool, nutrient-rich water off the Peruvian coast, causing fish stocks to decline and disrupting fisheries.
- Severe droughts in Indonesia and Australia. These hamper rice production and encourage wildfires. Although these fires are often set deliberately for slash-and-burn clearance, particularly in Indonesia, they frequently burn out of control. This also results in severe smoke pollution.
- A lower likelihood of severe hurricanes in the Atlantic; however, climate change is warming the Atlantic, which in turn increases hurricane risk.
- A higher likelihood of severe tropical cyclones in the Pacific, which are referred to as typhoons in the western Pacific and hurricanes in the eastern Pacific.
- Cold late winters in Europe, because the polar vortex, a band of strong winds encircling cold air masses over the Arctic, is disrupted. This allows cold polar air to surge southwards and warm air to flow northwards.
- A weakening of the monsoon in South Asia. It was this connection that led to the discovery of El Niño's global impacts and underlying causes. When several El Niño events occurred in rapid succession in the early 20th century, they triggered extreme droughts and severe famines. This prompted British meteorologist Sir Gilbert Walker to investigate the causes, leading to his discovery of the El Niño–Southern Oscillation (ENSO), its underlying mechanisms, and its link to the monsoon.
La Niña has opposite impacts in several respects. Because it represents an intensification of normal climatological conditions, its consequences are less pronounced:
- Less rainfall along the west coast of South America.
- Massive torrential rain across Southeast Asia and north-eastern Australia.
- An increased likelihood of severe hurricanes in the Atlantic.
Under what conditions does El Niño become particularly strong?
El Niño events are considered strong when the surface water temperature off the west coast of South America is more than 1.5 °C above average. This is favoured not only when warm water accumulates in the western Pacific, but also when a reservoir of warm water forms deep within the central Pacific. If this reservoir migrates eastwards and rises to the surface off South America, a strong El Niño is to be expected.
Is it already possible to assess whether El Niño will be particularly strong at the end of 2026?
As early as late July, surface temperatures in the south-eastern Pacific off the coast of South America were already 2 °C higher than normal, according to measurements from various meteorological institutions. In August, the National Oceanic and Atmospheric Administration (NOAA), the US weather service, observed weekly average surface temperatures along the Equator that were as much as 3 °C above average.
However, because of natural weather fluctuations, weekly surface temperatures are not considered particularly informative. Meteorologists therefore usually calculate temperature anomalies as three-month averages and base their forecasts on these intervals. According to these models, there is a greater than 90 per cent probability of a very strong El Niño by the end of 2026. This is further indicated by the fact that temperatures in deeper oceanic layers across large areas of the central and eastern Pacific are 8 °C above the long-term average.
Both NOAA and the UK Met Office, whose forecasts have proven highly reliable in the past, predict that sea temperatures will be 3 °C warmer by the end of the year, which would make it the strongest El Niño ever observed. The German Weather Service (Deutscher Wetterdienst) and several other institutions even forecast an El Niño with a strength of around 4 °C.
How does the strength of an El Niño affect its impacts?
The intensity of rainfall depends heavily on the surface temperature of the sea over which it forms, as the atmosphere then absorbs more moisture and the warmer temperature drives the water cycle. Rainfall along the west coast of South America is therefore particularly heavy during a strong El Niño.
The intensity of tropical cyclones also depends on the surface temperature of the sea over which they form, as cyclones draw energy from the ocean. Typhoons in the Pacific consequently become more destructive during a strong El Niño.
In many cases, however, a strong El Niño does not intensify the impacts so much as make them more likely. This applies, for example, to the cold late winters that El Niño can bring to Europe. As with many meteorological developments, whether this happens depends on numerous factors, of which El Niño is only one. During a strong El Niño, however, it becomes more likely that its influence will prevail. Furthermore, a strong El Niño lasts longer, meaning its meteorological consequences are expected to persist for longer.
What is known about how El Niño will change with climate change?
Studies using high-resolution climate models investigating this question predict that human-caused climate change could generally intensify El Niño events in the second half of the century.
In August 2026, a study was published in the journal Science in which a US team presented evidence of an increase in strong El Niño events since the 1980s. Researchers reconstructed surface temperatures in the eastern Pacific using the chemical composition of coral skeletons from the Galápagos Islands. The study also examined whether such data are suitable as a so-called proxy for sea surface temperatures in the first place. Individual strong El Niño events were indeed reflected in the geochemistry of the corals.
Daniela Matei, who researches the El Niño–Southern Oscillation at the Max Planck Institute for Meteorology, considers that the study could offer an outlook on the future development of ENSO under the influence of climate change. However, she also points out limitations to the research. For instance, several strong El Niño events around 1900 that are very well documented by observational data could not be detected in the coral data. Furthermore, the US team compared coral data with measured surface temperatures only for the period from 1984 to 2015, partly because proxy data were not continuously available, leaving two strong El Niño events (1982/83 and 2015/16) unrecorded.
Ultimately, whether strong El Niño events will increase with climate change remains a subject of ongoing research, in which the Max Planck Institute for Meteorology is actively involved.
Note: This is an updated version of an article originally published on 29 June 2023.
