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El Niño and La Niña: Frequently asked questions

What are el niño and la niña.

El Niño and La Niña are opposite phases of a natural climate pattern across the tropical Pacific Ocean that swings back and forth every 3-7 years on average. Together, they are called ENSO (pronounced “en-so”), which is short for E l N iño- S outhern  O scillation.

The ENSO pattern in the tropical Pacific can be in one of three states: El Niño, Neutral, or La Niña. El Niño (the warm phase) and La Niña (the cool phase) lead to significant differences from the average ocean temperatures, winds, surface pressure, and rainfall across parts of the tropical Pacific. Neutral indicates that conditions are near their long-term average.

Maps of sea surface temperature anomaly in the Pacific Ocean during a strong La Niña (top, December 1988) and El Niño (bottom, December 1997). Maps by NOAA Climate.gov, based on data provided by NOAA View.   large versions La Niña | El Niño

What happens during El Niño and La Niña?

During El Niño, the surface winds across the entire tropical Pacific are weaker than usual. Ocean temperatures in the central and eastern tropical Pacific Ocean are warmer than average, and rainfall is below average over Indonesia and above average over the central or eastern Pacific.

Rising air motion (which is linked to storms and rainfall) increases over the central or eastern Pacific, and surface pressure there tends to be lower than average.  Meanwhile, an increase in sinking air motion over Indonesia leads to higher surface pressure and dryness.  

Generalized Walker Circulation (December-February) anomaly during El Niño events, overlaid on map of average sea surface temperature anomalies. Anomalous ocean warming in the central and eastern Pacific (orange) help to shift a rising branch of the Walker Circulation to east of 180°, while sinking branches shift to over the Maritime continent and northern South America. NOAA Climate.gov drawing by Fiona Martin. 

During La Niña, it’s the opposite. The surface winds across the entire tropical Pacific are stronger than usual, and most of the tropical Pacific Ocean is cooler than average. Rainfall increases over Indonesia (where waters remain warm) and decreases over the central tropical Pacific (which is cool). Over Indonesia, there is more rising air motion and lower surface pressure. There is more sinking air motion over the cooler waters of the central and eastern Pacific.

Generalized Walker Circulation (December-February) anomaly during La Niña events, overlaid on map of average sea surface temperature anomalies. Anomalous ocean cooling (blue-green) in the central and eastern Pacific Ocean and warming over the western Pacific Ocean enhance the rising branch of the Walker circulation over the Maritime Continent and the sinking branch over the eastern Pacific Ocean. Enhanced rising motion is also observed over northern South America, while anomalous sinking motion is found over eastern Africa. NOAA Climate.gov drawing by Fiona Martin. 

Between the warm phase (El Niño) and cool phase (La Niña), scientists describe conditions as “ENSO-neutral.” Neutral means that the temperatures, winds, convection (rising air), and rainfall across the tropical Pacific are near their long-term averages.   

Generalized Walker Circulation (December-February) during ENSO-neutral conditions.  Convection associated with rising branches of the Walker Circulation is found over the Maritime continent, northern South America, and eastern Africa. NOAA Climate.gov drawing by Fiona Martin.

Is El Niño a kind of storm that will hit the U.S.?

No,  El Niño  isn’t a storm that will hit a specific area at a specific time. Instead, the warmer tropical Pacific waters cause changes to the global atmospheric circulation , resulting in a wide range of changes to global weather. Think of how a big construction project across town can change the flow of traffic near your house, with people being re-routed, side roads taking more traffic, and normal exits and on-ramps closed. Different neighborhoods will be affected most at different times of the day. You would feel the effects of the construction project through its changes to normal patterns, but you wouldn’t expect the construction project to "hit" your house.

Was that big storm we just had due to El Niño?

That isn't an answerable question. El Niño does increase the chances for a wet and stormy winter and early spring overall across the southern tier of the United States, but it's impossible to say that any single storm was solely caused by El Niño and wouldn't have happened otherwise.

Think of it this way: Suppose that in an average year, your state experiences 10 winter storms. During this El Niño winter, perhaps you get 13. It's impossible to say which 10 were your "normal" ones and which 3 were the "extra" ones.

However, for any specific storm, scientists can try to estimate if and how much El Niño contributed to making the event especially extreme, for example, by increasing the amount of water vapor available “in the background,” or by shifting the position or strength of the jet stream.

This sort of analysis is called an attribution study. It requires comprehensive observations—both current and historical—as well as highly detailed climate recreations of the weather patterns that gave rise to the storm. It may take scientists several months to conduct this kind of analysis.

How do El Niño and La Niña affect weather patterns?

El Niño and La Niña alternately warm and cool large areas of the tropical Pacific—the world’s largest ocean—which significantly influences where and how much it rains there. The primary location of moist, rising air (over the basin’s warmest water) is centered over the central or eastern Pacific during El Niño and over Indonesia and the western Pacific during La Niña.

This shift disrupts the atmospheric circulation patterns that connect the tropics with the middle latitudes, which in turn modifies the mid-latitude jet streams. By modifying the jet streams, ENSO can affect temperature and precipitation across the United States and other parts of the world. The influence on the U.S. is strongest during the winter (January-March), but it lingers into the early spring.

These maps illustrate the typical impacts of El Niño and La Niña on U.S. winter weather. Typical means "common," but not guaranteed because each event is unique. NOAA Climate.gov drawings, adapted from originals by the Climate Prediction Center.

During El Niño, the southern tier of Alaska and the U.S. Pacific Northwest tend to be warmer than average, whereas the U.S. southern tier of state—from California to the Carolinas—tends to be cooler and wetter than average.  During La Niña, these deviations from the average are approximately (but not exactly) reversed.

The influence of El Niño and La Niña in some parts of the United States and the rest of the world can be so strong that they increase the odds of “extreme weather events”—phenomena that rank in the highest or lowest 10% compared to historical observations.  (Click to view a  historical perspective on El Niño impacts in the U.S. )

However, not all of these influences are negative. For example, because the northern tier of the U.S. tends to be warmer than average during El Niño winters, heating costs there may be appreciably reduced.

How does ENSO affect global average temperature?

Within any given decade, the warmest years are usually El Niño ones, and the coldest are usually La Niña ones. That’s because the Pacific Ocean is a big place. If you walked around the planet along the equator, you’d be spending over 40% of your time attempting to walk on the water in the Pacific Ocean. This vast size means that warming or cooling in the Pacific due to El Niño and La Niña can leave an imprint on the global average surface temperature.

In general, the warmest year of any decade will be an El Niño year, the coldest a La Niña one. This graph shows annual average surface temperatures (gray bars), grouped by decade, from 1950 to 2021. The warmest and coldest years of each decade are topped with circles: red for El Niño-influenced years and blue for La Niña years. We considered a year El Niño or La Niña "influenced" if the December-February was labelled as part of a historical episode by NOAA's Climate Prediction Center or if more than half of the months in that year were. By our definition, 1979 did not qualify as El Niño year because El Niño conditions were present for only 3 months late in the year. 1992 was the coldest year of the 1990s despite being an El Niño year because of the cooling influence of the  eruption of Mount Pinatubo in 1991. NOAA Climate.gov graph based on data from NOAA National Centers for Environmental Information.

But the surface warming and cooling during El Niño and La Niña don’t involve more or less heat energy entering or escaping the climate system as a whole. In other words, the whole climate system isn’t really cooling or warming. Heat energy that's already present in the climate system is simply shifting back and forth between the atmosphere (where it  shows up in the global surface temperature value) and the deeper layers of the ocean (where it doesn't).

The changes in sea surface temperatures during El Niño and La Niña are caused and helped along by changes in the trade winds, which normally blow from east to west across the tropical Pacific Ocean. When the trade winds are stronger than normal during La Niña, the winds push more surface water to the western half of the Pacific basin. The pool of warm water grows deeper, storing excess heat at depth , and allowing for colder, deeper water to rise to the surface in the eastern half of the Pacific basin.

This wind-driven disturbance creates a large area along the equator where the ocean surface temperatures are below normal. Over the span of months to seasons, heat from the atmosphere then goes into the ocean, leading to cooler air temperatures over a region broad enough to cool down the global average temperature.

During El Niño, when the trade winds are weak or even occasionally reverse themselves, the amount of cold water that comes to the surface is reduced. Warm waters in the west Pacific Ocean slosh to the east. Now there is a large area along the equator where ocean temperatures are above normal. Heat from the ocean then goes out into the atmosphere, leading to warmer air temperatures in the Pacific and subsequently, to warmer global air temperatures (plus a cascade of other impacts ).

All of this amounts to a shuffling of heat from one place (ocean) to another (the atmosphere) without affecting the Earth's overall energy budget—the balance between incoming and outgoing energy across the entire planet. So unlike volcanic eruptions, which actually block energy from the Sun from reaching the surface, or solar minimums, which reduce the total amount of energy the Sun emits, the phases of ENSO are not creating or removing energy from the climate system.  La Niña hides some of Earth’s existing heat below the surface, while El Niño reveals it.  Climate scientists call this kind of re-shuffling  internal  climate variability.

Will El Niño affect my town/state/region this winter?

Maybe. Probably. Probably not. The answer depends on many factors, including where you live, how strong the event continues to be, and other climate patterns that develop and influence the seasonal outcome.

Scientists have identified a set of typical U.S. impacts that have been associated with past El Niño events. (See How do El Niño and La Niña affect weather patterns?) But “associated with” doesn’t mean that all of these impacts happen during every El Niño episode. They may happen as often as 80 percent of the time, or as infrequently as 40 percent of the time.

In other words, the influence of El Niño on U.S. winter climate is a matter of probability , not certainty. The Climate Prediction Center takes El Niño into consideration in their monthly and seasonal outlooks, which describe the likelihood that temperature and precipitation will be well-above or well- below average.

How does NOAA decide when El Niño is happening? 

NOAA uses a 5-category alert system for tracking ENSO that is based on a combination of observed conditions, computer model forecasts, and expert scientific judgment. For El Niño, the eastern tropical Pacific Ocean has to be 0.5°C or more warmer than average, and winds, surface pressure, and rainfall must have begun to show changes consistent with El Niño. (See What happens during El Niño and La Niña?) These changes in average conditions must persist for at least five overlapping three-month periods in order to be count as a full-blown episode in the historical record.

Summary of NOAA decision process in determining El Niño conditions. NOAA Climate.gov drawing by Glen Becker and Fiona Martin.

What causes El Niño and La Niña to occur?

The winds near the surface in the tropical Pacific usually blow from east to west. For reasons scientists don’t yet fully understand, these relatively steady winds sometimes weaken or strengthen for weeks or months in a row. 

Weak winds allow warm surface waters to build up in the eastern Pacific. Sometimes, but not always, the atmosphere responds to this warming with increased rising air motion and above-average rainfall in the eastern Pacific. This coordinated change in both ocean temperatures and the atmosphere begins an El Niño event. As the event develops, the warmed waters cause the winds to weaken even further, which can cause the waters to warm even more.

El Niño is often (but not always) followed by La Niña the following year, particularly if the El Niño is strong. During La Niña conditions, the easterly trade winds near the equator get even stronger than they usually are. Stronger winds push surface water into the western Pacific. Meanwhile, cool water from deeper in the ocean rises up in the eastern Pacific. If the cooling persists, it can inhibit rising air movement and rainfall in the eastern Pacific, beginning a La Niña event. As the event develops, the cooled waters cause the winds to strengthen even further, which can cause the waters to cool even more.

How long do El Niño and La Niña typically last?

El Niño and La Niña episodes typically last 9-12 months. They both tend to develop during the spring (March-June), reach peak intensity during the late autumn or winter (November-February), and then weaken during the spring or early summer (March-June).

Both El Niño and La Niña can last more than a year, but it is rare for El Niño events to last longer than a year or so, while it is common for La Niña to last for two years or more. The longest El Nino in the modern record lasted 18 months, while the longest la Niña lasted 33 months. Scientists aren’t sure why the duration of the two types of events can be so different.  

Can we predict El Niño and La Niña before they occur?

Yes, scientists can often predict the onset of El Niño and La Niña several months to a year in advance, thanks to modern climate models (such as those used by NOAA’s National Centers for Environmental Prediction ) and observation data from the Tropical Pacific Observing System (which includes sensors on satellites, ocean buoys, and radiosondes), which constantly monitors changing conditions in the ocean and atmosphere.  Without these tools we wouldn’t be able to detect or predict the onset of El Niño or La Niña.     

Why is predicting El Niño and La Niña so important?

El Niño and La Niña can make extreme weather events more likely in certain regions. If we can predict El Niño and La Niña, we can predict a greater chance of the associated extreme events. Better predictions of where and when extreme weather events are likely to happen (e.g., floods and droughts) could save the United States billions of dollars in damage costs. 

Predicting the life cycle and strength of El Niño and La Niña is critical for helping people plan for, avoid, or mitigate potential damages in every sector of society, including agriculture, fisheries, energy, water, transportation, and health care).  Advances in scientists’ ability to predict future ENSO states could significantly improve U.S. economic opportunities in these vital sectors.

Can we prevent El Niño and La Niña from occurring?

No, El Niño and La Niña are naturally occurring climate patterns and humans have no direct ability to influence their onset, intensity, or duration.

Does global warming affect El Niño and La Niña? 

There are many ways in which global warming could affect the frequency and intensity of El Niño / La Niña (see this ENSO blog post, for example), but scientists currently have low confidence in their ability to predict exactly how a warmer world affect the ENSO.  Scientists have high confidence, however, that ENSO itself has been occurring for thousands of years, and will continue into the future.  Global warming is likely to affect the impacts related to El Niño and La Niña, including extreme weather events.

Do El Niño and La Niña influence the Atlantic and Pacific hurricane seasons?

Yes, the continental United States and Caribbean Islands have a substantially decreased chance of experiencing a hurricane during El Niño and an increased chance of experiencing a hurricane during La Niña.

Typical influence of El Niño on Pacific and Atlantic seasonal hurricane activity. Map by NOAA Climate.gov, based on originals by Gerry Bell.

Both El Niño and La Niña influence where Atlantic hurricanes tend to form. During El Niño, fewer hurricanes develop in the deep tropics from African easterly waves. Conversely, during La Niña, more hurricanes form in the deep tropics from African easterly waves and, therefore, have a greater likelihood of becoming major hurricanes that may eventually threaten the Caribbean Islands and the United States.

Typical influence of La Niña on Pacific and Atlantic seasonal hurricane activity. Map by NOAA Climate.gov, based on originals by Gerry Bell.

Overall, El Niño contributes to more eastern and central Pacific hurricanes and fewer Atlantic hurricanes while, conversely, La Niña contributes to fewer eastern and central Pacific hurricanes and more Atlantic hurricanes.. 

Do El Niño and La Niña influence tornado activity in the U.S.?

Yes, El Niño and La Niña appear to have an effect on tornado activity. Since a strong jet stream is an important ingredient for severe weather, the position of the jet stream helps to determine the regions more likely to experience tornadoes. 

The jet stream over the United States is typically considerably different during El Niño winters as compared to La Niña winters. During El Niño, the jet stream is oriented from west to east across the southern portion of the United States.  Thus, this region becomes more susceptible to severe weather outbreaks during the winter.  Conversely, during La Niña, the jet stream and severe weather are likely to be farther north.  

Why are these climate patterns called “El Niño” and “La Niña”?

Centuries before it was a focus of scientific study, South American fishermen noticed warmer-than-normal coastal Pacific Ocean waters and dramatic decreases in fish catch occurring periodically around Christmas time.  They nicknamed the phenomenon “El Niño” (Spanish for little boy) in connection with the celebration of the Christian holiday marking the birth of Jesus.  In the 1980s, when the opposite phase of El Niño was discovered (i.e., cooler-than-normal ocean temperatures), scientists called it “La Niña” (Spanish for little girl).   

Where can I find more information about El Niño and La Niña? 

NOAA’s primary point-of-entry for online information about ENSO is available at http://www.climate.gov/enso . NOAA Climate.gov publishes a frequently updated “ ENSO blog, ” written by climate scientists in language easy to understand by non-scientists. ENSO forecasts, outlooks, and diagnostic discussion information is available from NOAA’s Climate Prediction Center, at: http://www.cpc.ncep.noaa.gov . Maps showing El Niño and La Niña historical impacts on weather patterns in the United States are available from NOAA’s National Center for Environmental Information ( here ) and NOAA’s Earth System Research Laboratory ( here ).

Older ENSO FAQs from other NOAA labs and centers

The El Niño FAQ from AOML El Niño FAQ from PMEL El Niño and La Niña FAQs from CPC FAQs about El Niño and the western U.S., Alaska, and Hawaii ENSO FAQ from ESRL  

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El Niño and La Niña: Their Impact on the Environment

We know that there are many anthropogenic forcings on the climate, particularly the volume of carbon and greenhouse gases pumped into the atmosphere as a part of our everyday lives. Yet there are a number of natural processes that affect local weather, regional climate and global conditions. Some effects on our climate are a result of fluctuations and anomalies in the complex water conveyor belts of the ocean currents of the world. These fluctuations are known as “oscillations” and the two best-known oscillations are El Niño and La Niña (1) (2).

The latter is the opposite of the former and make up an oscillation known as ENSO. Understanding them requires knowledge of a broad range of data from multiple disciplines. Typically, researchers who understand the processes and study their causes and effects have post-graduate degrees in such disciplines as oceanography, geography, climatology and meteorology. The phenomena and the data extrapolated from them, have applications for palaeoclimatology (the study of climate in the past), anthropology, palaeobotany and archaeology, particularly in what we can extrapolate from the changes to tree ring data (dendrochronology) (3).

El Niño and La Niña: What Are They?

Both El Niño and La Niña are opposite effects of the same phenomenon: the ENSO (El Niño Southern Oscillation). Both are an oscillation in the temperatures between the atmosphere and the ocean of the eastern equatorial Pacific region, roughly between the International Dateline and 120 degrees west (2). El Niño - the conditions for which build up between June and December (15) - is caused by a change in the wind patterns (5). Here, the Pacific Trade Winds fail to replenish following the summer monsoons of Asia (7). This warmer air leads to an oscillation between the cooler and warmer waters, leading to warmer ocean temperatures than normal.

La Niña is effectively the opposite of El Niño, indicated by prolonged periods of sea temperatures in the same region (2), and the effects stated above are generally reversed. During non El Niño years, atmospheric pressure is lower than normal over the western Pacific area and higher over the colder waters of the western Pacific, as already discussed. With La Niña, the Trade Winds are particularly strong in carrying warmer water westwards across the Pacific leading to colder than average temperatures in the east and warmer than average temperatures in the west (9). The result is that plankton increases in the areas where the temperature is cooler, leading to a positive effect on the marine life that depends on plankton or depends on those creatures that depend on plankton (11).

It is commonly expected that La Niña will follow immediately on from an El Niño event, but this is not always the case (14). Typically, both occur every three to five years but they have varied anything between two and seven years. Both phenomena last anything between nine and twelve months.

How Does El Niño Affect Conditions?

Typically, it comes around every five years and what usually happens is that warming in the oceans caused by the winds leads to diffusion of this warming all over the globe. It changes atmospheric pressures with consequences for rainfall, wind patterns, sea surface temperatures and can sometimes have a positive, and sometimes a negative effect on those systems (4). In Europe for example, El Niño reduces the instances of hurricanes in the Atlantic (8). The beginning of the El Niño system will be seen over North America in the preceding winter (2); typically they include:

• Mild winter temperatures over western Canada and north western USA • Above average precipitation in the Gulf Coast, including Florida • A drier than average period in Ohio and pacific northwest

How Does La Niña Affect Conditions?

Like El Niño, it too affects atmospheric pressure and temperature, rainfall and ocean temperature. In Europe, El Niño reduces the number of autumnal hurricanes. La Niña has less of an effect in Europe but it does tend to lead to milder winters in Northern Europe (the United Kingdom especially) and colder winters in southern/western Europe (12) leading to snow in the Mediterranean region. Elsewhere in the world, areas that are affected by La Niña experience the opposite of the effects they experience with El Niño (9). It is continental North America where most of these conditions are felt. The wider effects include (1):

• Stronger winds along the equatorial region, especially in the Pacific • Decreased convection in the Pacific leading to a weaker jet stream • temperatures are above average in the southeast and below average in the northwest • Conditions are more favourable for hurricanes in the Caribbean and central Atlantic area • Greater instances of tornados in those states of the US already vulnerable to them

In the western Pacific, the formation of cyclones shifts westwards which increases the potential for landfall in those areas most vulnerable to their affects, and especially into continental Asia and China (13). There is greater rainfall in the west too, especially in Australia, Indonesia and Malaysia (10) and further westwards toward the southern countries in the African continent. Consequently, over the US and Canada there will be lower than average precipitation and this pattern follows the coast southwards where the western portion of South America will also experience lower than average rainfall.

Climate Change

How El Niño and La Niña will change or affect climate change in the future is now of tremendous importance thanks to the known effects over the last century or more - and the conditions are still not very well understood, though the phenomenon has been known since the early 1600s (2). For climate scientists, this is a grey area as to whether it will have an impact on the climate, or whether they will be affected by climate change (14). Some recent research has suggested that the effects of the ENSO will worsen as the climate changes (16).

It is important for lives and livelihood, for economies and insurers to understand the potential for damage caused by extreme weather such as El Niño and La Niña so their continued study is of vital importance. Historical records have built up to the point that researchers have a clear idea of what the likely effects of each ENSO is likely to be in any given year. A paper in 2013 compiled the effects from records going back 700 years and how they have impacted global conditions in this time (2). The question is not settled, though many scientific institutes have devoted much time to the study of the ENSO (15) and conflicting data says that ENSO may become the increasing norm.

• http://oceanservice.noaa.gov/facts/ninonina.html
• https://www.nature.com/articles/nclimate1936
• http://www.whoi.edu/main/topic/el-nino-other-oscillations
• http://skepticalscience.com/this-year-el-nino-real-enigma.html
• http://www.cpc.ncep.noaa.gov/products/analysis_monitoring/lanina/enso_evolution-status-fcsts-web.pdf
• http://earthobservatory.nasa.gov/Features/ElNino/
• http://earthobservatory.nasa.gov/Features/ElNino/elnino2.php
• https://earthobservatory.nasa.gov/Features/LaNina/la_nina_2.php
• http://www.nasa.gov/vision/earth/lookingatearth/plankton_elnino.html
• https://journals.ametsoc.org/view/journals/clim/17/6/1520-0442_2004_017_1419_ioenoe_2.0.co_2.xml
• http://www.realclimate.org/index.php/archives/2006/05/el-nino-global-warming/
• http://www.climatecentral.org/news/is-texas-toast
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What is El Niño and how is it influenced by climate change?

El Niño has officially been declared in 2023. This naturally occurring climate phase brings warmer weather throughout the globe and can increase the risk of extreme weather. This section explains how El Niño happens, and what affect it can have on global temperatures that are already rising due to human-caused climate change. 

FAQs on wildfires

What is el niño.

El Niño and La Niña are two phases of the naturally occurring climate phenomenon called the El Niño–Southern Oscillation (ENSO), which leads to the most dramatic year-to-year variation of Earth’s climate. El Niño is characterised by warmer global temperatures, while La Niña years are typically cooler.

In neutral years that are neither El Niño nor La Niña, strong Pacific winds along the equator push warm water from east to west, leading to an upwelling of deeper cooler waters in the eastern Pacific while warm water gathers in the western Pacific. The warm water heats up the air above the western Pacific, which in turn regulates weather patterns by driving atmospheric circulation. However, every few years (two to seven on average) the Pacific winds ease, reducing the upwelling of cooler waters in the east and causing sea surface temperatures to rise and become consistent across the Pacific Ocean. [1] These conditions are known as El Niño.

During the El Niño phase, the warmer temperatures in the eastern Pacific Ocean cause changes in atmospheric circulation patterns which strongly influence global weather patterns. El Niño impacts are usually felt for around 6-12 months and are strongest along the equator on either side of the Pacific. [2]

In Australia and Southeast Asia, hotter and drier conditions raise the risk of drought, heatwaves, and wildfires. [3] On the west coast of South America, wetter conditions result in heavy rainfall and increased flood risk. [4] The effects are less extreme elsewhere, but El Niño can induce shifts in the position of winds from the west in the northern hemisphere known as the polar front jet stream. By pushing this jet stream southward, El Niño can bring about heavy rainfall in the southern United States and increased temperatures in the northern United States and Canada. [5] In Europe, the effects are comparatively much milder but can drive colder winters and stronger heat waves in summer. [6]

La Niña has a less dramatic effect on extreme weather events, though it can still influence global weather patterns. During La Niña years, the easterly winds across the Pacific Ocean become stronger. This cools ocean temperatures in the eastern Pacific while pushing warmer waters further to the western Pacific, leading to increased rainfall and risks of cyclones in Pacific islands, Australia, and New Zealand. [7] Conversely, drier conditions and droughts are observed along the west coast of South America and the Gulf Coast of the United States. [8]

There is a high level of uncertainty regarding the likelihood of an ENSO event occurring and the magnitude of that event [9] [10] . To monitor ENSO, researchers routinely measure sea surface temperatures, and oceanic pressure using satellite imagery and a system of buoys positioned across the Pacific Ocean [11] [12] . Using these measurements researchers calculate indices and provide forecasts and warnings about the potential impacts and timings of El Niño and La Niña. These forecasts help governments and communities prepare for extreme weather events.

Key to monitoring ENSO is a stretch of the Pacific Ocean at the equator known as ‘Niño 3.4’ which is regularly monitored to calculate the Oceanic Niño Index (ONI), a 3-month running mean of sea surface temperatures compared to long-term averages. El Niño and La Niña events are defined when the ONI index exceeds +/- 0.5 o C for a period of five months or more. [13]

References:

[1] Timmermann, A., et al. (2018). El Niño–southern oscillation complexity. Nature, 559 , 535-545. https://doi.org/10.1038/s41586-018-0252-6

[2] WMO. (2023). World Meteorological Organization declares onset of El Niño conditions. https://public.wmo.int/en/media/press-release/world-meteorological-organization-declares-onset-of-el-niño-conditions

[3] Australian Government Bureau of Meteorology. (2021). What is El Niño and how does it impact Australia? http://www.bom.gov.au/climate/updates/articles/a008-el-nino-and-australia.shtml

[4] 4. Cai, W., et al. (2020). Climate impacts of the El Niño–Southern Oscillation on South America. Nature Reviews Earth & Environment , 1, 215-231. https://doi.org/10.1038/s43017-020-0040-3

[5] Halpert, M. (2014). United States El Niño Impacts. National Oceanic and Atmospheric Administration. https://www.climate.gov/news-features/blogs/enso/united-states-el-niño-impacts-0

[6] Brönnimann, S. (2007). Impact of El Niño–Southern Oscillation on European climate. Reviews of Geophysics , 45 , RG3003. https://doi.org/10.1029/2006RG000199

[7] Kuleshov, Y., et al. (2014). Extreme Weather and Climate Events and Their Impacts on Island Countries in the Western Pacific: Cyclones, Floods and Droughts. Atmospheric and Climate Sciences , 4 , 51441. https://doi.org/10.4236/acs.2014.45071

[8] McPhaden, M.J. (2002). El Niño and La Niña: causes and global consequences. Encyclopedia of global environmental change , 1 , 353-370. https://www.pmel.noaa.gov/gtmba/files/PDF/pubs/ElNinoLaNina.pdf

[9] Timmermann, A., et al. (2018). El Niño–southern oscillation complexity. Nature, 559 , 535-545. https://doi.org/10.1038/s41586-018-0252-6

[10] Capotondi, A. (2023). Simplifying climate complexity.  Nature Geoscience ,  16 , 280-281. https://doi.org/10.1038/s41561-023-01161-y

[11] National Oceanic and Atmospheric Administration. (2023). El Niño/Southern Oscillation (ENSO). https://www.ncei.noaa.gov/access/monitoring/enso/

[12] Voosen, P. (2023). Critical El Niño monitor gets an upgrade. Science , 380, 445-445. 10.1126/science.adi5370

[13] National Oceanic and Atmospheric Administration. (2023). El Niño/Southern Oscillation (ENSO). https://www.ncei.noaa.gov/access/monitoring/enso/

How does climate change influence El Niño?

The relationship between climate change and stronger El Niño is a topic of ongoing scientific research. While there is no definitive agreement in the scientific community, recent studies suggest that global heating may be leading to stronger El Niño events.

One recent study found that current sea surface temperature extremes driven by El Niño have intensified by around 10% compared to pre-1960 levels. [1] This builds on previous studies which predicted that the frequency of extreme El Niño events could double over the next century due to faster surface warming of the eastern Pacific Ocean brought on by global temperature rises. [2]

However, it can take up to a decade for the El Niño-Southern Oscillation (ENSO) to shift from El Niño to La Niña and back again, and the intensity of La Niña and El Niño events can vary substantially. [3]

This variable nature of ENSO means it is difficult for scientists to confidently connect the intensity of ENSO phases with climate change. However, the Intergovernmental Panel on Climate Change predicts the frequency of strong El Niño and La Niña events is likely to increase throughout the next century. [4]

Many scientists believe the effects of climate change will be intensified by El Niño because increased global temperatures are themselves associated with increased extreme weather events [5] [6] . Therefore, the coinciding effects of both elevated temperatures and El Niño events are predicted to induce record breaking spikes in global temperatures [7] , and a further increased probability that catastrophic weather conditions will occur. [8]

The last strong El Niño in 2015/2016 coincided with the hottest year on record and resulted in widespread droughts, wildfires, floods, and agricultural disruption, leading to ecosystem instability in some regions [9] [10] . Estimates from the UN suggest that this El Niño phase significantly impacted the lives of over 60 million people via socioeconomic damage, migration, disease outbreaks and food insecurity. [11] The extreme impact of this ‘super’ El Niño is widely linked to a strong El Niño event on top of ongoing global warming caused by human activity, such as burning fossil fuels. [12]

Record-breaking global temperatures have been observed even during La Niña years, demonstrating the long-term warming trend driven by climate change. For example, the La Niña year in 2022 was ranked as the fifth warmest year on record. [13]

On 4 July 2023, the World Meteorological Organization announced the onset of an El Niño phase and estimated that there is a 90% chance El Niño will continue at moderate or high strength up to the end of the year. A variety of El Niño indices, including the Oceanic Niño Index (ONI), also predict with high certainty that an extended El Niño period with extreme weather conditions will last well into 2024. [14] Global average temperatures have already reached record-breaking levels in 2023 [15] and with a strong El Niño phase, it is likely the world will experience climatic instability equal to or greater to 2016, with widespread floods and droughts predicted to cause vast economic damage and food insecurity. [16] [17]  

[1] Cai, W., et al. 2023. Anthropogenic impacts on twentieth-century ENSO variability changes. Nature Reviews Earth & Environment , 4 , 407-418. https://doi.org/10.1038/s43017-023-00427-8

[2] Cai, W., et al. 2014. Increasing frequency of extreme El Niño events due to greenhouse warming. Nature Climate Change , 4 , 111-116. https://doi.org/10.1038/nclimate2100

[3] Klingsman, N., Will, K. (2018). El Niño 2018-2019: Historical impact analysis, in Strengthening Resilience and response to crises. UK Government: Department for International Development. https://www.dai.com/uploads/DFID_El%20Nino_2018_Historical%20Impact%20Analysis%20(University%20of%20Reading).pdf

[4] Masson-Delmotte, V., et al. (2021). Climate change 2021: the physical science basis. Contribution of working group I to the sixth assessment report of the intergovernmental panel on climate change, 2021. 2. https://www.ipcc.ch/report/ar6/wg1/downloads/report/IPCC_AR6_WGI_FrontMatter.pdf

[5] Diffenbaugh, N.S., et al. (2017). Quantifying the influence of global warming on unprecedented extreme climate events. Proceedings of the National Academy of Sciences , 114 , 4881-4886. https://doi.org/10.1073/pnas.1618082114

[6] Knutson, T.R., et al. (2021). Climate change is probably increasing the intensity of tropical cyclones. Critical Issues in Climate Change Science , Science Brief Review, 4570334. https://news.sciencebrief.org/cyclones-mar2021/

[7] WMO (2023). WMO Global Annual to Decadal Climate Update. Target years: 2023-2027. https://library.wmo.int/index.php?lvl=notice_display&id=22272

[8] Rifai, S. W., Li, S., & Malhi, Y. (2019). Coupling of El Niño events and long-term warming leads to pervasive climate extremes in the terrestrial tropics.  Environmental Research Letters ,  14 , 105002. https://doi.org/10.1088/1748-9326/ab402f

[9] Santoso, A., McPhaden, M.J. & Cai, W. (2017). The Defining Characteristics of ENSO Extremes and the Strong 2015/2016 El Niño. Reviews of Geophysics , 55 , 1079-1129. https://doi.org/10.1002/2017RG000560

[10] Field, R. D., Van Der Werf, G. R., Fanin, T., Fetzer, E. J., Fuller, R., Jethva, H., … & Worden, H. M. (2016). Indonesian fire activity and smoke pollution in 2015 show persistent nonlinear sensitivity to El Niño-induced drought.  Proceedings of the National Academy of Sciences ,  113 , 9204-9209. https://doi.org/10.1073/pnas.1524888113

[11] OCHA. (2016). El Niño: Overview of Impact, Projected Humanitarian Needs and Response. https://reliefweb.int/report/world/el-ni-o-overview-impact-projected-humanitarian-needs-and-response-16-august-2016

[12] Funk, C.C. (2021). Climate Change Made the 2015–2016 El Niño More Extreme, in Drought, Flood, Fire: How Climate Change Contributes to Catastrophes. Cambridge University Press , 186-211.

[13] NASA. (2022). NASA Says 2022 Fifth Warmest Year on Record, Warming Trend Continues. https://www.nasa.gov/press-release/nasa-says-2022-fifth-warmest-year-on-record-warming-trend-continues

[14] NOAA. (2023). El Niño/Southern Oscillation (ENSO) diagnostic discussion. https://www.cpc.ncep.noaa.gov/products/analysis_monitoring/enso_advisory/ensodisc.shtml

[15]   NOAA. (2023). OISST V2.1. Climate reanalyzer.org, University of Maine, Climate Change Institute. https://climatereanalyzer.org/clim/sst_daily/

[16] Economist Intelligence (2023). El Niño: South and South-east Asia’s 2023 wildcard. https://www.eiu.com/n/el-nino-south-and-south-east-asias-2023-wild-card/

[17] FAO. (2023). Threat of El Niño looms, FAO prepares anticipatory actions with Members and partners. https://www.fao.org/documents/card/en/c/cc5749en

Read more about these topics by exploring the explainers published by our sister institute, the Grantham Research Institute at LSE: 

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How is climate change affecting the oceans.

The world’s oceans form a primary component of the climate system, but how is climate change affecting them, and what are the impacts for people?

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'Loss and Damage' refers to the negative consequences of climate change on human societies and the natural environment. How can loss and damage from climate change be reduced, and how is this issue covered in international climate negotiations?

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What is El Niño—and will it lead to more snow this winter?

Here’s a look at what these weather events are, why they happen, and whether scientists think they’re getting stronger.

We're currently experiencing the effects of an El Niño weather pattern , which tends to create warmer-than-average weather.  

Layered on top of climate change, this year's El Niño has already helped contribute to record warm temperatures as warm water locked in the deep ocean rises to the surface.

But hot weather isn't the only impact of an El Niño—some parts of the country may have an above average chance of seeing more snowfall. Thanks to its influence on the jet stream, El Niño winters typically result in dryer conditions in the north, and wetter conditions along the California coast and in the south.  

This year, the National Oceanic and Atmospheric Administration   expects the odds of snow to increase in the Southwest and Mid-Atlantic and decrease over the Rocky Mountains, Midwest, and New England.  

While El Niño raises the odds for snow in certain regions, it's not a guarantee that more snow will indeed fall. Overall, a warming climate has nudged annual snowfall totals down in many states.  

Learn more about how El Niños form and how they influence our weather.

For Hungry Minds

What is el niño.

El Niño events are actually just one half—the warm, wet half—of a naturally occurring weather cycle called the “ El Niño-Southern Oscillation ,” or ENSO.

During an El Niño event, the surface of the tropical Pacific Ocean gets warmer than usual, particularly at the equator and along the coasts of South and Central America. Warm oceans lead to low pressure systems in the atmosphere above, which in turn leads to a lot of rain for the western coasts of the Americas.

During some of the most famous El Niños of the past, the deluges have been so strong that entire villages have slid down mountainsides . In the 1972 to 1973 event, ocean temperatures skyrocketed off the Peruvian coast, nearly wiping out the anchoveta fishing industry , a critical one for the country. During the 1997 to 1998 El Niño, the country sustained over $3.5 billion in damage to buildings, agricultural lands, and other infrastructure. And in 2016, corals bleached across the Pacific, floods ravaged South America, and drought-fueled fires ripped across Australia .

The events can last for as long as a year, though the warming tends to be strongest during the Northern Hemisphere’s fall and winter months— October through February . In fact, that timing is the source of the name: “El Niño” means “male child” in Spanish, and also refers to the baby Jesus. Fishermen in South America, who have long known and described the phenomenon, called it “El Niño” because the some of the biggest effects spin up around Christmas—and the name stuck.

What about La Niña?

The other half of the ENSO phenomenon is generally called “La Niña.” It’s basically the opposite of an El Niño: Ocean temperatures along the eastern half of the tropical Pacific cool down and that part of the world dries out. The band of heat and rain swings over to the other side of the ocean, meaning that Australia, Indonesia, and southeastern Asia get wetter and warmer than usual.

La Niña events tend to settle in for longer than El Niños, persisting for somewhere between nine months to two years .

El Niños and La Niñas generally occur about every two to seven years. In between, ocean temperatures and rainfall patterns become more average. The patterns aren’t perfectly clear, though—a strong El Niño doesn’t necessarily mean the following La Niña will be particularly intense, and vice versa .

Both El Niños and La Niñas affect weather far beyond the Pacific basin. During El Niño years, for example, fewer hurricanes whirl across the Atlantic than usual, and the ones that do are likely to be fairly weak. And rainfall patterns shift across the globe : California and the Horn of Africa dampen, for example, while the rains that generally drench India during monsoon season weaken, and the Indian subcontinent dries out slightly.

Why El Niños happen

At the start of an El Niño, the trade winds that usually whisk briskly across the surface of the tropical Pacific slacken. Usually, those winds push warm surface ocean waters eastward toward Asia and Australia, where they essentially get corralled into a giant warm pool by Australia to the south, the Indonesian archipelago near the equator, and southeastern Asia.

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In a normal year, as the trade winds drag waters from the sun-warmed surface eastward, away from the edge of South and Central America, they draw up cold water from deep below, “ upwelling ” the chilly, nutrient-rich seas. The trade winds also usually induce upwelling of deep, cold waters near the equator.

During a normal year it’s cool and not too rainy along the western coast of the Americas, and warm and wet in the western part of the Pacific.

But when the trade winds die, two things happen: The wind-forced upwelling that draws cool water to the surface slows down, and the warm water that has pooled up in the western part of the Pacific basin starts to slosh back toward the east. And as the warmth spreads eastward, the trade winds—which are partly controlled by the temperature and air pressure differences between the two sides of the Pacific—get even weaker. So there’s a double whammy: the chilly waters that usually help cool down the South American coast stay trapped deep below the surface, and the winds that would help cool things down stagnate.

Scientists still don’t know exactly what kicks off the cycle. But they can pick out the signs of a brewing El Niño early and they have a good idea of how the events develop once they’re nudged into action. So once the signs appear, scientists can start warning the general public that an El Niño is likely to pop up about six to nine months later.

How El Niños influence climate—and vice versa

Some climate models predict that the ENSO cycle will intensify as the planet gets hotter, leading to even warmer, wetter El Niños and drier La Niñas—and more devastating impacts on communities around the world. Others show less intensification, or none at all. Scientists are racing to understand the phenomenon better.

It’s also not yet clear whether the cycle has intensified since humans started warming the planet by pumping the atmosphere full of greenhouse gases .

What scientists can say is that ENSO has existed for thousands of years and is likely to persist far into the future . And whether or not the actual cycle changes, we’ll likely feel its effects more strongly in the future .

Already the world has warmed 1.2, and scientists sa y additional warming from an El Niño might provide a preview of what life will be like at 1.5°C, an aspirational limit to global warming set by the Paris Climate Agreement.

2016 was the last time an El Niño event caused such deadly heat, and that year may hold clues for what’s in store.  

Temperature readings for oceans around the Great Barrier Reef in Australia and at islands from Fiji to Hawaii were sky-high—hotter, in many cases, than ever before recorded.

Oceans have been warming up quickly and steadily because of climate change, and research suggests El Niño events are getting rainier and hotter.  

The effects of El Niño events ripple across the planet, changing weather patterns from Dakar to Delhi to Boston and beyond. These powerful events happen naturally, but climate change may tweak their strength and ferocity in the future.

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Study says El Nino, not climate change, was key driver of low rainfall that snarled Panama Canal

Cargo ships wait in Panama Bay before moving through the Panama Canal in Panama City, Sept. 23, 2023. (AP Photo/Arnulfo Franco)

FILE - Cargo ships wait in Panama Bay before moving through the Panama Canal in Panama City, Sept. 23, 2023. The climate phenomenon known as El Niño — and not climate change — was a key factor driving low rainfall that disrupted shipping at the Panama Canal, scientists said Wednesday, May 1, 2024. (AP Photo/Arnulfo Franco, File)

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FILE - A cargo ship sails toward the Pacific Ocean after moving though the Panama Canal, seen from Panama City, Aug. 3, 2023. The climate phenomenon known as El Niño — and not climate change — was a key factor driving low rainfall that disrupted shipping at the Panama Canal, scientists said Wednesday, May 1, 2024. (AP Photo/Arnulfo Franco, File)

FILE - Storm clouds gather overhead as cargo ships that wait to move through the Panama Canal are anchored on the Atlantic side of the Panama Canal, seen from Colon, Panama, Sept. 4, 2023. The climate phenomenon known as El Niño — and not climate change — was a key factor driving low rainfall that disrupted shipping at the Panama Canal, scientists said Wednesday, May 1, 2024. (AP Photo/Arnulfo Franco, File)

WASHINGTON (AP) — The climate phenomenon known as El Nino — and not climate change — was a key driver in low rainfall that disrupted shipping at the Panama Canal last year, scientists said Wednesday.

A team of international scientists found that El Nino — a natural warming of the central Pacific that changes weather worldwide — doubled the likelihood of the low precipitation Panama received during last year’s rainy season. That dryness reduced water levels at the reservoir that feeds freshwater to the Panama Canal and provides drinking water for more than half of the Central American country.

Human-caused climate change was not a primary driver of the Central American country’s unusually dry monsoon season, the World Weather Attribution group concluded, after comparing the rainfall levels to climate models for a simulated world without current warming.

The study has not been published in a peer-reviewed scientific journal yet but follows scientifically accepted techniques, and past such studies have frequently been published months later.

A cargo ship sails toward the Pacific Ocean after moving though the Panama Canal, seen from Panama City, Aug. 3, 2023. (AP Photo/Arnulfo Franco)

“Natural variability plays a critical role in driving many extremes,” said Kim Cobb, a climate scientist at Brown University, who was not involved in the study. “This is an important reminder that climate change isn’t always the answer.”

Panama experienced one of its driest years on record last year, receiving below-average rainfall for seven of the eight months of its May to December rainy season.

As a result, since last June, the Panama Canal Authority has restricted the number and size of ships passing through the Panama Canal due to low water levels in Lake Gatun , the canal’s main hydrological reserve. Global shipping is still being disrupted.

To test whether climate change had a role, the team of scientists analyzed weather data against computer simulations precise enough to capture precipitation in the region. Such models simulate a world without the current 1.2 degrees Celsius (2.2 degrees Fahrenheit) of warming since preindustrial times, and see how likely the lack of rainfall would be in a world without fossil fuel-charged warming.

The climate models did not show a trend similar to the drying that Panama experienced last year. In fact, many models show a wetter trend in the region due to climate change from carbon dioxide and methane emissions produced by the burning of coal, oil and natural gas .

Meanwhile, the analysis showed that El Nino reduced the 2023 rainfall by about 8%, and that it’s unlikely Panama would have experienced such a dry rainy season without the influence of the weather phenomenon. The researchers said increased demand for water in the region worsened the shortfall.

Storm clouds gather overhead as cargo ships that wait to move through the Panama Canal are anchored on the Atlantic side of the Panama Canal, seen from Colon, Panama, Sept. 4, 2023. (AP Photo/Arnulfo Franco)

The group used more than 140 years of rainfall records collected from 65 weather stations — a “statistician’s dream,” said Clair Barnes, a researcher at Imperial College of London and one of the study’s authors.

“So we’re very confident that El Nino is driving the low precipitation,” said climate scientist Friederike Otto, also of Imperial College, who coordinates the attribution study team.

The World Weather Attribution group launched in 2015 largely due to frustration that it took so long to determine whether climate change was behind an extreme weather event. Studies like theirs, within attribution science, use real-world weather observations and computer modeling to determine the likelihood of a particular happening before and after climate change, and whether global warming affected its intensity.

The Associated Press’ climate and environmental coverage receives financial support from multiple private foundations. AP is solely responsible for all content. Find AP’s standards for working with philanthropies, a list of supporters and funded coverage areas at AP.org .

Summer of 2023 Was Hottest in 2,000 Years

By Ernie Mundell HealthDay Reporter

TUESDAY, May 14, 2024 (HealthDay News) -- High temperatures across the Northern Hemisphere last summer were scorching and frequent enough to make it the hottest summer in two millennia, new research shows.

Weather records based on scientific instruments only goes back as far as 1850, noted researchers at Cambridge University in England. That data already had confirmed the summer of 2023 as the hottest ever recorded.

However, the Cambridge crew turned to tree ring data to reach back 2,000 years and last summer was still the hottest over that entire period of time.

“When you look at the long sweep of history, you can see just how dramatic recent global warming is,” said study co-author Ulf Büntgen , a professor of geography at Cambridge. “2023 was an exceptionally hot year, and this trend will continue unless we reduce greenhouse gas emissions dramatically.”

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His team published its findings May 14 in the journal Nature .

As Büntgen's group explained, it can be easy for climate change skeptics to criticize "hottest year ever" claims if records don't go further back than 1850.

“Many of the conversations we have around global warming are tied to a baseline temperature from the mid-19th century, but why is this the baseline? What is normal, in the context of a constantly changing climate, when we’ve only got 150 years of meteorological measurements?” Büntgen noted in a Cambridge news release.

“Only when we look at climate reconstructions [from much deeper into the past] can we better account for natural variability and put recent anthropogenic climate change into context," he said.

To help reach farther back into the past, Büntgen's group compared known instrumental data on weather against tree ring growth patterns for the same years.

They found that reading tree rings was accurate in spotting weather trends.

For example, tree ring changes accurately reflected the "Little Antique Ice Age" cooling period of the 6th century, as well as the Little Ice Age of the early 19th century. These cooling periods typically follow large volcanic eruptions, which spew ash and other contaminants into the atmosphere, cooling the Earth down.

In contrast, the Northern Hemisphere heats up during El Niño weather changes, which was also recorded on tree rings.

“It’s true that the climate is always changing, but the warming in 2023, caused by greenhouse gases, is additionally amplified by El Niño conditions, so we end up with longer and more severe heat waves and extended periods of drought,” said study lead author Jan Esper , of Johannes Gutenberg University Mainz in Germany. “When you look at the big picture, it shows just how urgent it is that we reduce greenhouse gas emissions immediately.”

The study also found that in the Northern Hemisphere, the 2015 Paris Agreement to limit warming to 1.5 degrees Celsius above pre-industrial levels has already been surpassed.

Because the current El Niño period isn't expected to subside until well into this summer, the summer of 2024 could also be a record-breaker, the researchers said.

More information

Find out more about climate change at the Environmental Defense Fund .

SOURCE: University of Cambridge, news release, May 14, 2023

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