Effects
- Planetary Boundaries & Tipping Points
- Extreme weather & event attribution
- ENSO: El Niño & La Niña
- Feedback effects of warming
- Wildfires increasing
- Antarctica melting
- Antarctic sea ice disappearing
- Arctic sea ice disappearing
- Greenland melting
- Ocean currents changing
- Oceans warming
- Ocean acidification
- Melting permafrost & burning ice
- New Zealand’s disappearing glaciers
- Black carbon & ash on snow
- Seasons changing
- How we know about past climates: proxy data
Home > Climate wiki > Effects > ENSO
Summary
Effects
- Planetary Boundaries & Tipping Points
- Extreme weather & event attribution
- ENSO: El Niño & La Niña
- Feedback effects of warming
- Wildfires increasing
- Antarctica melting
- Antarctic sea ice disappearing
- Arctic sea ice disappearing
- Greenland melting
- Ocean currents changing
- Oceans warming
- Ocean acidification
- Melting permafrost & burning ice
- New Zealand’s disappearing glaciers
- Black carbon & ash on snow
- Seasons changing
- How we know about past climates: proxy data
Home > Climate wiki > Effects > ENSO
Summary
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Due to the Coriolis Effect, the Trade Winds blow east-to-west across the Pacific. These surface winds push warm tropical surface water west, where it builds up above northern Australia and Indonesia, raising sea levels 40-60cm higher than the eastern Pacific. Warm water leads to more evaporation, resulting in monsoon rainfall and tropical cyclones (Fig. 1). On the eastern side of the Pacific, cool water from the deep is drawn to the surface, bringing vast quantities of fish.
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During ENSO neutral conditions the Trade Winds push warm tropical water west to east, where warm moist air rises, generating monsoon rainfall over Asia and northern Australia. Image: NOAA.
In the 1600s South American fishermen noticed a periodic warming of these (eastern) coastal Pacific waters, and with it, fewer fish. As it occurred around Christmas they named it El Niño; Spanish for ‘Little Boy’ or the ‘Christ Child’.
Others noticed that the Trade Winds had reversed, which explained why warm water from around Indonesia was pushed back towards South America (Fig. 2).
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During El Niño conditions the Trade Winds reverse, pushing warm tropical waters (yellow areas) east across the central Pacific. (Warm water can be much further south than this diagram shows). This reversal in Trade Winds also reverses the Pacific Walker Circulation, which in turn changes global weather systems. Image: NOAA.
The reversal of the Trade Winds changes the Walker Circulation. This generally inhibits the formation of cyclones and typhoons in the Pacific, and hurricanes in the Atlantic Oceans. However, fed by so much heat in the ocean, those that do form are amongst the most powerful and destructive.
The peaks in temperatures during El Niños are often followed by the cooling effects of La Niñas (Fig. 3). While the wind patterns are similar to ENSO neutral conditions (Fig. 1), they are more intense, leading to more powerful cyclones, typhoons, hurricanes, and stronger monsoon rains.
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Fig. 3: La Niña conditions push more warm water west, allowing cooler waters in the east to rise to the surface. This extra warm water in the west can result in more cyclones forming, some of which may track down to Aotearoa, fed by the heat in the ocean. Image: NOAA.
By 1969 the ENSO phenomena was broadly understood. But exactly what triggers it remains unclear. Still, by examining past weather records the overall pattern was consistent—until the late 1970s when each El Nino seemed to permanently ratchet up global temperatures (Fig. 4).
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Global temperature anomalies ENSO 1950-2026. Image: Our World in Data
By the 1970s it was also becoming clear that the increasing volume of greenhouse gases in the atmosphere was preventing some of the heat from the sun escaping back into space. Around 89% of this heat was being absorbed by the oceans as far down as 300-700m. By the mid-1990s that excess heat was penetrating waters below 2000m (Fig. 5). As the energy imbalance is increasing, more heat is continuously being added every year.
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The amount of heat that the ocean, land, ice, and atmosphere has been absorbing from 1960-2020 in Zetajoules. 1 Zetajoule = 1 billion petajoules. A petajoule = 1 million billion joules or 278 gigawatt hours of energy. Image: von Schuckmann et al. 2023
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In 2025 the ocean took up around 23 Zettajoules (278 billion gigawatts) of heat. That’s the equivalent heat of ~12 Hiroshima sized atomic bombs exploding in the ocean every second. Water has a very high specific heat capacity, so the ocean can store massive amounts of this thermal energy with relatively small changes in temperature (although due to thermal expansion this is contributing to accelerating sea level rise).
The 2023-2024 El Niño released a tiny portion of this excess heat into the atmosphere, helping to push global temperatures past 1.5°C for the first time (Fig. 6). Late in 2024 La Niña set in, but global temperatures barely dropped below 1.5°C.
“Cool” years are now hotter than the “warm” years of the past: tracking global temperatures through El Niño and La Niña. – OurWorld in Data, 03 March 2025
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Annual average temperatures to 2025. Image: Copernicus
- April 2025: the weak short-lived La Niña had vanished and the Walker circulation had resumed its normal ENSO neutral pattern (Background | Fig. 1). However, it was clear that unless a stronger La Niña returned, global average temperatures had been permanently reset to a new high (Fig. 6).
We typically gain much clearer insight between late May and June, once interactions between the ocean and atmosphere strengthen. This coupling–such as weakening trade winds and warming of the central Pacific–provides the physical evidence needed for confidence to increase. – EMCWS, 10 April 2026
- March 2026: it was becoming increasingly clear that another El Niño was on its way. Historically, El Niños appear every two to seven years, so this was not unprecedented. The models used to predict changes to the ENSO pattern are notoriously unreliable during March-May. So the budding El Niño might have faded away, although there was so much heat in the ocean that seemed unlikely.
- 01 June 2026: an ‘historic’ extreme signal in the models indicated El Niño’s imminent arrival (Fig. 7).
- 12 June 2026: El Niño offcially begins.
Fig. 7: 01 June 2026: multiple model runs show unprecedented (‘historic’) temperature anomalies in the ‘Nino 3.4’ region [Fig. 8]. Image: Jeff Berardelli.
Fig. 8: The section of the Pacific monitored for changing ENSO Conditions ‘Nino 3.4’ Image: NOAA -
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El Niño is arriving at a time when global temperatures are exceptionally high (Fig. 6). Sea surface temperatures (SSTs) around Aotearoa were also unusually high the time of writing (they are normally cooler during El Niños: Fig. 2). Hence there is a considerably uncertainty how it will play out. An El Niño was declared by NIWA/Earth Sciences New Zealand 02 July 2026 Video 2.
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Fig. 6: Annual average temperatures to 2025. Image: Copernicus
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Fig. 2: During El Niño conditions the Trade Winds reverse, pushing warm tropical waters (yellow areas) east across the central Pacific. (Warm water can be much further south than this diagram shows). This reversal in Trade Winds also reverses the Pacific Walker Circulation, which in turn changes global weather systems. Image: NOAA.
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02 July 2026 meteorologists walk through the full winter outlook including El Niño.
Further resources:
- Climate Central ‘climate shift index’ online mapping tool updates SSTs every few days
- NIWA seasonal climate outlook
- NIWA SST forecasts
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More information
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Some incoming radiation from the sun is reflected back into space due to the albedo effect of the cryosphere (ice caps, permafrost, glaciers) and atmospheric aerosols much of which, paradoxically, come from burning fossil fuels. About 89% of the retained excess heat is being absorbed by the oceans. The land takes up ~6%, the cryosphere absorbs ~4%—which is why it’s rapidly melting—and the remaining 1% is in the atmosphere.
The imbalance leads to energy accumulation in the atmosphere, oceans and land, and melting of the cryosphere, resulting in increasing temperatures, rising sea levels, and more extreme weather. – Mauritsen et al 2025
The role of the land, ocean, and cryosphere taking up most of the heat is included in climate models. However:
Worryingly, the observed energy imbalance is rising much faster than expected, reaching 1.8 W/m2 in 2023—or twice that predicted by climate models—after having more than doubled within just two decades. – op. cit.
While the land and oceans absorbed 95% of the excess heat, they’re also doing double duty by absorbing (mostly via plants) 38% of the excess CO2 we’re putting into the atmosphere. If not for them, temperatures would be much higher (see Greenhouses gases and how they work).
In 2024, the global annual growth rate of atmospheric CO2 surged to a record of 3.73 ppm year—the highest since 1959—exceeding the 1.5°C climate threshold for the first time. – Dang et al April 2026
While human emissions were still climbing, they weren’t enough to account for all that extra CO2. Dang et al all found that from 2014-2023 the land had been absorbing and average 3.22Gt/year of carbon. But in 2024—the year that temperatures spiked above 1.5°C (Fig. 9)—the land suddenly stopped absorbing about a third of the CO2 that it had done over the previous ten years of measurements.
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Fig. 6: Annual average temperatures to 2025. Image: Copernicus
This explained the increasing energy imbalance (Fig. 10) and corresponding sudden increase in temperatures. The 6% of heat that the land had been taking up was driving up ground surface temperatures, increasing soil respiration, and triggering decomposition of soil organic matter—which released CO2. Together with melting permafrost and an increase in wildfires and ongoing destruction of forests, the land has not only stopped absorbing as much CO2, it’s now releasing some of the long-held CO2 back into the atmosphere. A tipping point had been crossed.
….the underlying mechanism for the reduction was caused by hotter and drier conditions leading to a larger increase in respiration than photosynthesis….These results challenge previous assumptions about the long-term stability of the terrestrial carbon sink. – op cit.
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Fig. 9: The imbalance between the incoming radiation (black line) and outgoing infrared radiation (red line). The imbalance leads to energy accumulation in the atmosphere, oceans, and land, leading to rising temperatures (Image: Leon Simmons, February 2025).
This had already been raised in 2021 at COP 26, but was ignored:
The only reason why the IPCC provides the world with the remaining carbon budget* of roughly 4 – 500 gigatonnes, is that the models assume that the carbon sink capacity of intact nature will continue. So not only are we assuming that biological systems will not cross tipping points, we’re also assuming that the stocks of carbon in forests in soils, in wetlands and permafrost, remain reasonably intact over the next 50 years. That is quite an optimistic assumption because it means we need to invest in conserving the remaining intact ecosystems. – Rockström, COP 26 (see Tipping points).
* The ‘carbon budget’ was the assumed amount of carbon that we could keep releasing into the atmosphere to keep temperatures under 1.5°C , on the assumption that the land and ocean would keep absorbing it.
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- 2026; Steinert et al; Permafrost carbon–climate feedback amplifies Earth system tipping risks, Environmental Research Letters 21 | 12
- 2026; Tsuchida et al; Multi-year La Niña–El Niño transition influenced Earth’s extreme energy uptake in 2022–2023 Nature Geoscience 19 pp432–438
- 2026: Forster et al; Indicators of Global Climate Change 2025: annual update of key indicators of the state of the climate system and human influence Earth Systen Science Data 11 June 2026 (open access)
- 2026: Cheng et al; Ocean Heat Content Sets Another Record in 2025, Advances in Atmospheric Sciences 09 January
- Plain English: 2026: Live Science; Last year, the oceans absorbed a record-breaking amount of heat — equivalent to 12 Hiroshima bombs exploding every second
- 2026: European Centre for Medium-Range Weather Forecasts (ECMWF); How confident should we be in a prediction of El Niño?
- 2026: Berkeley Earth Global Temperature Report 2025
- 2026: Copernicus Climate Change Service 14 January
- 2026: ECMWF ‘2025 Global Climate Highlights’
- 2025: Mauritsen et al; Earth’s Energy Imbalance More Than Doubled in Recent Decades, AGU Advances: (open access)
- Plain English article from the authors: Earth is trapping much more heat than climate models forecast – and the rate has doubled in 20 years; University of NSW
- 2025: Peng et al; Strong 2023–2024 El Niño generated by ocean dynamics Nature Geoscience 23 May
- 2025: Lu et al; Increased frequency of multi-year El Niño–Southern Oscillation events across the Holocene Nature Geoscience 18 pp337-343 (Open access)
- 2025: Samborskaand Ritchie: “Cool” years are now hotter than the “warm” years of the past: tracking global temperatures through El Niño and La Niña The world is warming despite natural fluctuations from the El Niño cycle. Our World in Data
- 2024: Frankopan, The Earth Transformed: An Untold History. Bloomsbury, 736pp
- 2024: Pearce; Pollution Paradox: How Cleaning Up Smog Drives Ocean Warming, Yale Environment 360
- 2023: Schuckmann et al; Heat stored in the Earth system 1960–2020: where does the energy go? Earth Systems Science Data 15 pp1675-1709
- NIWA: What are El Niño and La Niña
- NIWA: The impact of El Niño and La Niña on New Zealand’s climate
- 2022: Lopez et al; Projections of faster onset and slower decay of El Niño in the 21st century, Nature Communications v13 no. 1915
- 2020: England et al; Tropical climate responses to projected Arctic and Antarctic sea-ice loss, Nature Geoscience 13 pp275-281
- 2020: McFadden et al (eds) El Niño Southern Oscillation in a Changing Climate, AGU book series
- 2020: Cai et al; Butterfly effect and a self-modulating El Niño response to global warming Nature 585 pp68–73
- 2019: Adamson; El Niño and Society, Oxford Research Encylopedia of Climate Science Edition: 1
- 2014: Trenberth et al; Earth’s Energy Imbalance: American Meteorological Society Journal of Climate 27 | 9 pp 3129-3144