The El Niño Fast Track: Could a 2026 El Niño deliver another global warming shockwave?
NOAA are predicting the return of El Niño in 2026, the first since 2023. What could this spell for global temperatures and weather extremes?
What is ENSO?
El Niño and the Southern Oscillation (ENSO) is a periodic fluctuation in sea surface temperatures and the air pressure of the overlying atmosphere across the equatorial Pacific Ocean. In this way it is a combination of two phenomena that actually reinforce each other. There are three states of the ENSO system, the most well known warm El Niño, the slightly less well known cool La Niña and the unremarkable neutral condition.
ENSO is one of the most important climate phenomena on Earth due to its ability to change the global atmospheric circulation, which in turn, influences temperature, precipitation and other aspects of the climate all around the globe.
The discovery and linking of the systems was only complete in the 1960s. Much earlier, South American fisherman noticed the warming of coastal waters occurred every so often around Christmas. They referred to the warming as “El Niño,” (niño being Spanish for a boy child) in connection with the Christmas holiday.
Sir Gilbert Walker discovered the “Southern Oscillation,” or large-scale changes in sea level atmospheric pressure across Indonesia and the tropical Pacific. However, he did not link it to the changes in the Pacific Ocean temperature or El Niño events. It wasn’t until the late 1960s that Jacob Bjerknes realised that the changes in the ocean and the atmosphere were connected and the hybrid term “ENSO” was born. It wasn’t until the 1980s that the terms La Niña and Neutral gained popularity.
The Southern Oscillation aspect describes a bimodal variation in sea level air pressure between Australia and Tahiti. Normally, under neutral conditions, lower atmospheric pressure is present over Eastern Australia and higher pressure exists over Tahiti. This drives a trade wind running from east to west. The wind pushes surface waters with it in a westerly direction across the equatorial Pacific. This warm water flow brings rain to Australia and the Western Pacific. It also draws cold deep water to the surface along the South American coast which replaces the warm surface waters flowing westward. A La Niña accentuates these effects drawing more cool water to the eastern surface and driving more rain into the west.
Every 2 to 7 years, apparently at random, although work is progressing to provide longer and longer predictions, these trade winds weaken and in some cases reverse. This in turn slows the ocean current that draws surface water away from the western coast of South America and reduces the upwelling of cold, nutrient–rich water from the deeper ocean, flattening out the thermocline and allowing warm surface water to build in the eastern part of the Pacific - the temperature rise noticed by the fishermen which they called El Niño.
El Niño conditions change the precipitation patterns across the ocean, leading to much dryer conditions in the western Pacific and Australia and wetter conditions in the East, including the Gulf of Mexico.
The warm sea surface temperature emits more heat as long wave radiation which escapes to space, but as greenhouse gases increase, more of this heat is trapped by the atmosphere pushing up global mean temperatures.
How is ENSO monitored?
Although the Southern Oscillation is an air pressure difference and monitored through an index, the SOI, the main monitoring tool is measurements of sea surface temperature anomalies in four regions of the Pacific. Even though there are four zones, the principle index is known as Niño 3.4 which comprises portions of zone 3 and zone 4 as shown in the map below. The index is basically the difference in sea surface temperature between the area inside the Niño 3.4 box and the surrounding Pacific Ocean.
An El Niño is present when the three month rolling average Niño 3.4 is above 0.5°C. A La Niña is declared when the three month rolling average is below -0.5°C. Anomalies over ±1.5° are strong and ±2° are very strong. Anything in between 0.5° and -0.5° is defined as neutral.
NOAA, among other international and national weather services, provides a weekly ENSO report1 together with historical records and forecasts for the coming 9 months. Below is the latest forecast issued in November 2025. The current report shows La Niña conditions are forecast to be present until the spring of 2026, but there is a rising chance that the late autumn and winter of 2026 will see the return of El Niño.
El Niños effect on global temperatures
Since El Niño events temporarily increases the peak global surface air temperature (SAT), successive events have provided glimpses of the future climates that we are heading into. The super-strong 2015/16 event, which recorded a Niño 3.4 reading of 2.7°C drove an increase in peak SAT of 0.35°C. This led to the 18 month mean surrounding the El Niño event of 1.25°C above pre-industrial, the first time this had been reached. It wasn’t until 2020 that the underlying trend passed this level of warming.
The 2023 El Niño was only just over 2°C, ranking just 5th out of the 7 strong events on record since 1950. Plotting the strength against the temperature peak shows it sat nicely on the normal line adding just 0.14° to the peak SAT. Together with other warming acceleration effects such as aerosol reduction and continued greenhouse gas emissions, it was however strong enough to give us the first taste of a 1.5°C world. This was especially the case since the previous years had witnessed prolonged La Niña conditions which meant that when the El Niño broke through it influenced temperatures for longer, increasing the annual average as well as the peak2.
Global implications of a 2026 El Niño
Global temperatures
What can we expect in terms of global temperature if there is an El Niño in late 2026? Given the relatively short period since the last El Niño - just 3 years, the bump in peak temperature is unlikely to be as high as the 2024 SAT. The graph below shows how a 2015 or 2023 scale event could influence global temperatures. The yellow and red lines show where SAT could peak to, over the next 25 years, tracking the underlying acceleration of global warming. Essentially a strong El Niño produces a peak yearly SAT 3 years ahead of the trend and a very strong El Niño, 6 years ahead of the trend.
A strong El Niño in late 2026 on a par with the 2023 event could drive the 2027 temperature to +1.66°C while a very strong, 2015 scale event, could drive 2027 to +1.78°C. So if an El Niño does develop next year, 2027 would be likely to set a new hottest year record, but not break through the +2°C upper Paris commitment level.
The first El Niño supported +2°C year would take a very strong event in 2031 or a strong event in 2034. The underlying trend would then catch up in 2038, the current trajectory timing for passing 2°C permanently.
Precipitation effects
Since ENSO moves rain systems back and forth along the equator, it’s no surprise that this has the strongest effect in both South America and Australia and Indonesia. Changes sit on top of natural variability but certainly affect the trend and likelihood of both wet and dry conditions.
In South America an El Niño brings warm and very wet weather, especially along the coasts of Peru and Ecuador. The high sea surface temperatures promote thunderstorm development adding to the likelihood of extreme rainfall events. These often cause major flooding during strong El Niño years.
Dryer and hotter conditions are experienced in parts of the Amazon basin, Columbia and central south America while southern Brazil and northern Argentina experience a wetter season.
Australia and the western Pacific have the opposite impacts - drought, especially in the north and east of the continent. Many of the worst recorded wildfires occur during El Niño events due to the increased temperatures and lack of rainfall.
North America is also affected but to a lesser extent, increased rainfall is likely along the gulf coast. Canada generally experiences a milder winter.
Ecological effects
El Niño reduces the upwelling of cold, nutrient-rich water that sustains large fish populations, which in turn sustain abundant sea birds, whose droppings support the fertiliser industry. The reduction in upwelling leads to mass fish die-offs off the shore of Peru and negatively effect fisheries, especially for local populations.
The droughts in the western Pacific affect forest health leading to increases in wildfires but also seedling mortality and a period of carbon source rather than sink. Droughts also affect the northern Amazon increasing pressure of water availability and increasing the likelihood of fire damage.
Coral Bleaching
Tropical coral reefs have already passed their tipping point leading to collapse and die off. Any natural variability, but especially an El Niño event, puts additional pressure on the systems, speeding their collapse. Previous mass bleaching events have corresponded to El Niño events so another one so soon after the 2023-25 bleaching event is only bad news for the coral, the ecosystem that it supports and the hundreds of millions who rely on it for income and food.
Hurricane season
Generally, over the North Atlantic, fewer tropical cyclones tend to form during El Niño years, while more tropical cyclones form during La Niña years. It has also been shown that the landfall probability of hurricanes in the United States decreases during El Niño events, while the converse is true during La Niña events. Xiong Wang et al.3 found that La Niña dissipation phases are associated with increased frequency, longer lifetime, and stronger intensity of hurricanes over the North Atlantic. Their tracks are also more likely to pass through the Caribbean Sea, Mississippi River, and eastern main development region.
The ENSO state in the previous winter is a strong indicator for the year’s season. With La Niña currently present and likely this winter, the 2026 season is likely to be lively but 2027 calmer if an El Niño does develop.
Disease outbreaks including Dengue fever
The warming caused by El Niño increases the range of disease vectors, especially mosquitos. Dengue fever has been spreading rapidly over the last decade, affecting millions rather than tens of thousands. Spikes in infection rates coincide with El Niño in addition to general global warming. The plot below shows this relationship clearly. A 2026 event could see many millions of cases in ever wider areas.
Antarctic Sea Ice
ENSO also has effects as far away as Antarctica. El Niño conditions result in high-pressure anomalies over the Amundsen and Bellingshausen Seas, causing reduced sea ice and increased poleward heat fluxes in these sectors, as well as the Ross Sea. The Weddell Sea, conversely, tends to become colder with more sea ice during El Niño.
A prolonged El Niño in the early 1940s has been linked to the start of the Thwaites Glacier instability and the 2015 event is linked to the sudden collapse in sea ice cover since then.
Given the rapidly declining sea ice extent around Antarctica since 2016, further disturbances are concerning. Reduced sea ice affects bottom water formation, carbon sequestration and ice sheet stability. All impact ice melt rates and accelerate sea level rise.
Economic effects
The extensive warming and reduced upwelling of nutrients along the eastern Pacific coastline can negatively effect the economics of local fishing and the international marine food markets. Coupled with on-land agricultural impacts, El Niño can affect commodity prices and the macroeconomy of many different countries. It can constrain the supply of rain-driven agricultural commodities, reduce agricultural output, construction, and services activities, increase food prices, and can even trigger social unrest in commodity-dependent poor countries that primarily rely on imported food.
Meanwhile other countries can benefit from El Niño who are able to capitalise on the shortages and increased prices, for example Argentina, the US and Mexico.
Conclusions
ENSO is the most impactful natural variation in the world’s climate. During the current period of accelerating warming it is even more pronounced. The relative cooling provided by 46 months of neutral and La Niña conditions before the 2023 El Niño led to the shockwave that that event caused.
A 2026 El Niño, after a three year break, will have serious impacts. Sea Surface temperatures are already as high as they were in 2023 despite the current cooling phase. An event in 2026 sitting on top of this will drive a further spike in global warming, increasing both air and sea temperatures.
It is unlikely that it will push annual temperatures in 2027 above +2°C, but an average between 1.6° and 1.8°C in 2027 is likely.
Impacts will include further tropical coral bleaching, pushing this essential ecosystem further past its tipping point towards complete die-off. It will drive droughts in Australia, Indonesia and the Brazilian Amazon increasing the likelihood of fire damage. It will drive a further growth spike in infectious diseases such as Dengue fever which will reach into higher latitudes.
The 2026 hurricane season may be lively with more storms forming in the Gulf of Mexico and making landfall. Given continuous increases in sea surface temperatures in that region, storm intensification and strength will be high. 2027 might see a calmer season however.
Which ever way you cut it, a 2026 El Niño is not good news.
ENSO Report for November 2025 https://www.cpc.ncep.noaa.gov/products/analysis_monitoring/lanina/enso_evolution-status-fcsts-web.pdf
Shiv Priyam Raghuraman et al. The 2023 global warming spike was driven by the El Niño–Southern Oscillation, Atmospheric Chemistry and Physics Vol 24 I 19, 2024. https://acp.copernicus.org/articles/24/11275/2024/
Wang X, Quan M, Fan K. Effects of El Niño–Southern Oscillation Dissipation Phases on Tropical Cyclone Activity over the North Atlantic. Ocean-Land-Atmos. Res. 2025;4:Article 0082. https://doi. org/10.34133/olar.0082
HI Tom, I have been giving much thought to the sensitivity issue from a hydro/ecological perspective, as you know that I believe that our focus on co2 as the main problem is in itself becoming part of the problem. If we see our adverse impact on this planet as a sensitivity enhancer then this becomes a multiplier on the co2 sensitivity . Say co2 sensitivity is 3 and our environmental impact is creating increased sensitivity in regards to incoming solar radiation through ecological and hydrological changes is 2 then the overall sensitivity is 5 or 6 depending on a time feedback loop. This is a number being thrown around a lot in regards to the rate of increase we are currently experiencing. If we can turn our land and ocean impact sensitivity into a fraction instead of a multiplier through work aligned with hydrological as well as ecological repair then we allow ourselves ample time to bring about a safe and profitable transition. Deforestation of tropical rainforest for biofuels is an example of how wrong I think our understanding is and the danger we are amplifying through our lack of understanding. Maybe we should think again about a sensitivity piece.
The way I see it each el Nino gives us a glimpse of what neutral years would be without sulfate aerosol pollution; what el Nino temperatures would bring without the disguising mask of fossil fuel pollution are hotter again.