El Niño and La Niña Phenomena on Top of Climate Change

According to the Meteorologist at the National Oceanic and Atmospheric Administration (NOAA) Matthew Rosencrans: “ We do expect the El Niño to at least continue through the northern hemisphere winter. There’s a 90% chance or greater of that.”

You might be aware that El Niño is a Spanish word that means “Boy”, with its female homolog, La Niña, obviously meaning “Girl”. Those concepts are tightly in touch with a recurrent climate pattern that implicates fluctuations in the temperature of waters within the central and eastern tropical Pacific Ocean; and show significant effects around the globe. This naming is in origin El Niño de Navidad, or “The Christmas Child” and emerged in the 1600s in South America when fishermen of the Pacific Ocean, around Peru and El Ecuador, were aware of unusual periods of water warmth during Christmas time, associated with a scarcity in fish amount.

Furthermore, Sir Gilbert Thomas Walker, a prominent Physicist and Statistician, achieved in 1930 an outstanding discovery about the so-called “Southern Oscillation” which refers to large-scale variations in sea level pressure across Indonesia and the tropical Pacific. At that time, he had not yet recognized its connection to changes in the Pacific Ocean. It was only in the late 1960s that Jacob Bjerknes and other researchers realized the interconnectedness between oceanic and atmospheric changes, leading to the creation of the hybrid term “ENSO”, short for “Southern Oscillation Cycle”. Subsequently, as of the 1980s, the new terms La Niña and Neutral stepped into the limelight within the scientific community. The warm phase of ENSO is called El Niño and the cold one is namely La Niña, with an intermediate neutral phase.

1. What is the effect of the ENSO Cycle?

The ENSO cycle has an impact on the environment and humans in El Niño, La Niña, and the neutral condition all over the globe, thus, impacting the global weather patterns; including the atmospheric circulation which affects temperature and precipitation due to the interactions between the ocean and atmosphere. As a matter of fact, in the central and eastern tropical Pacific Ocean area, when there is an increase in rainfall, La Niña contributes to the cooling of the ocean surface to or below-average Sea Surface Temperatures (SST). On the opposite side, over the Indonesian region and the central and eastern tropical Pacific Ocean, there would be a trend of decrease in rainfall, and vice-versa. In normal conditions, the flood carries water from the depths to the surface within the so-called Upwelling phenomenon, thus, bringing cold water characterized with high nutrient amounts to the surface and cooling the SST.

Schematic diagram of ENSO cycle in the equatorial Pacific (Source: (The Open University (1989): Ocean Circulation. Pergamon Press, Oxford, 238 pp; Kawahata and Gupta, 2014))

ENSO Cycle Description:

• The so-called Trade Winds (also known as “easellies”, which are the prevailing east-to-west winds) blow from the eastern part of the globe, particularly the Pacific along the equator line. They are the result of the difference in temperature between the equator and the poles. When they get weak in respect of normal conditions could even go the opposite way-, they result in atmosphere pressure and wind speed fluctuations.

Trade Winds: from east to west near the equator (Source: NASA/JPL-Caltech)

• Much of the warm water will remain in the eastern part of the Pacific Ocean and not migrate to the Asian compartment due to those atmospheric conditions.
• The cold water supposed to get to the surface during the Upwelling Phenomenon will not go up.
• By getting warmer, water reduces the winds more, resulting in more warm water in the eastern part of the Pacific.
• The heat from water spreads to the atmosphere resulting in more moisture and higher temperatures.
• Temperature Distribution on Earth gets disturbed: The atmosphere encounters issues with well-allocating heat over the globe, which increases both temperature and moisture in the south of Pacific equatorial regions and engenders the opposite in regions far away from the equator: less heat and more precipitations, this phenomenon is called La Niña.
• Warm water decreases the winds increasingly and we come up to a continuous circle.
• Out of the natural state of equilibrium where cold water upwells from the bottom to the surface to cool water, comes the two opposite El Niño and La Niña phenomena that disturb this balance: it is the ENSO cycle short for El Niño- La Niña Southern Oscillation cycle. They are the 2 extremities of the ENSO cycle, the balance phase is called ENSO-neutral.
• “Niña” and “Niño” refer to two phases of the ENSO, where the water goes through a warming and cooling pattern. El Niño event is officially recognized when sea surface temperatures in the tropical eastern Pacific increase by at least 0.5°C above the long-term average. In general, El Niño is more frequent than La Niña.
• La Niña is often associated with wet conditions in eastern Australia and heavy rainfall in Indonesia, the Philippines, Malaysia, and central Pacific islands such as Fiji, Tonga, and Papua New Guinea; thus, generating heat and drought. On the contrary, winter is drier than in usual conditions in areas such as southeastern Africa and northern Brazil, nevertheless, there are more precipitations than in normal conditions along the Gulf Coast of the US, the west coast of tropical South America such as Colombia, Ecuador, and Peru; and from southern Brazil to central Argentina together with some areas of eastern Africa including Kenya and Uganda. In northwestern Canada and Alaska, winters are warmer, inducing less cold Arctic air.
• La Niña was predominant on the planet, however, according to the World Meteorological Organization (WMO), the United Nations (UN), the European Space Agency (ESA), and NASA; we are getting back to El Niño.
• They were warning of higher temperatures over the globe and particularly along the tropical area. Even though this phenomenon is happening in the south of the Pacific Ocean, its effects are diffused and perceived all around the globe. The most recent significant El Niño event occurred in 1997/98, leading to the most severe documented coral bleaching and death, and the loss was estimated between 16% and 90% for areas such as the Maldives. Indeed, at a depth of 150m, the water temperatures recorded were approximately 3 °C, which contrasts with the typical rise of 0.25 °C often linked to El Niño occurrences.
• El Niño has an actual impact on ocean temperatures; and ocean currents’ speed and strength. It occurs at irregular intervals, typically ranging from 2 to 7 years, and can last between 9 and 12 months but can go beyond this period. However, unlike predictable climate cycles such for instances, the ENSO cycle is neither a regular nor an easily predictable phenomenon.

2. How to Monitor/Predict the ENSO Cycle?

The prediction of El Niño is ensured by several methods such as:

2.1. Buoys:

• Floating devices implemented in around 70 locations in the Pacific Ocean, there are many types of them: (1) Mooring buoys serve as secure points for boats, protecting marine ecosystems and detecting El Niño by measuring sea surface temperature anomalies. (2) Drifting buoys, equipped with sensors, provide real-time data on ocean conditions, supporting weather forecasting and El Niño detection. (3) Expendable buoys collect valuable oceanic data, detecting El Niño by measuring sea surface temperature anomalies for short-term monitoring and research targets.

2.2. Sea level monitoring:

• Detects El Niño by measuring the rise in sea level caused by the warming of ocean waters during El Niño events.

2.3. Satellites:

• Mainly the Sentinel-6 Michael Frelich which can identify the ability of Kelvin waves using radar altimeters via microwave signals to measure and monitor the ocean’s surface height.

Sentinel-6 Michael Frelich Satellite (Source: NASA Jet Propulsion Laboratory)

When it comes to assessment metrics, the most comprehensive index available is the MEI, short for the Multivariate ENSO Index. This index considers a range of meteorological and oceanographic factors, making it a highly effective tool for monitoring ENSO.

3. What triggers El Niño?

According to the NOAA, El Niño is triggered by a complex interaction between the ocean and the atmosphere in the tropical Pacific region which effects are spread over the globe. The main reason is the weakening of the Trade Winds normally blowing from east to west across the tropical Pacific Ocean. This wind speed is a function of the pressure gradient of the atmosphere along the 60-degree line. Those winds are the combined result of the Coriolis effect and the presence of a high-pressure area. The Coriolis Effect is due to the planet’s rotation which deviates/deflects air from the Earth’s movement on its axis, pushing it to the right in the Northern Hemisphere and the left in the Southern Hemisphere as follows:

Coriolis Effect Visualization (Source: NOAA)

4. Characteristics of EL Niño:

4.1. Kelvin and Rossby Oceanic Waves:

• Generates Rossby waves also known as planetary waves which result from the rotation of the planet.
• In a Rossby wave, there is a considerable difference in the velocity between the upper and lower parts of this huge wave, with the top portion displaying conspicuously slower movement in one direction while the bottom part moves in the opposite direction.

4.2. Ocean Currents:

• Trigger descending motion in the Pacific and ascending motion in the Atlantic.

4.3. Surface Heating:

• EL Niño is typically detected when the ocean’s surface temperature rises more than half a degree Celsius above the normal level.
• Conversely, La Niña occurs when the ocean’s surface temperature falls half a degree Celsius below the normal level.

4.4. Impact on North America:

• The impact reaches its peak during the winter season, raising several weather conditions throughout the US. While its effects are temporary, the most pronounced consequences are observed in the winter months, sometimes extending into early spring.

4.5. Impact on India:

• Indian Monsoons are weaker, thus, impacting other regions of south and south-east Asia and Australia. In La Niña Monsoons in India are better than normal.

4.6. Ecosystem:

• Cold water flow is slowed or stopped and the nutrients from the depth are fewer, which triggers less phytoplankton off the coast. Fish feeding on phytoplankton are, thus, affected leading to a looming food scarcity, and the food chain is disturbed.
• Waters with warmer heat bring tropical species, like yellowtail and albacore tuna, into areas that are normally too cold.

5. El Niño versus La Niña: Which one is Better?

• Whether La Niña or El Niño is considered “best” depends on the perspective and the specific needs or community preferences of different regions and industries.
• It’s important to note that both La Niña and El Niño can have far-reaching effects on weather patterns, ecosystems, agriculture, water resources, and various sectors of the economy. The preference for one over the other largely depends on the requirements and vulnerabilities of different regions and industries.
• La Niña and El Niño events are part of the natural climate variability, and both can play important roles in the overall balance and functioning of the Earth’s climate system. Neither one is intrinsically “better” than the other, due to their distinct roles and different impacts across the Earth.
• Scientists and meteorologists closely monitor and study those phenomena for a better understanding of their effects and betterment of preparedness and resilience in the face of their impacts.
• Just like El Niño, La Niña events don’t occur the same as one another and in the same previous area, dry conditions are replaced with wet, mild to weak rainfalls are replaced with heavy ones; heavy rains are replaced with rainfall deficiency.

El Niño versus La Niña (Source: NOAA)

5.1. El Niño:

a. Positive Aspects

• Can lead to drier and warmer conditions in some areas, which may be advantageous for some particular agricultural contexts and outdoor events.
• Can result in milder winters in certain regions, reducing the severity of cold temperatures.

b. Negative Aspects

• Can bring droughts, heatwaves, and water scarcity, thus, negatively impacting agriculture, water, and ecosystems.
• Can increase the risk of wildfires and contribute to extreme weather events.

5.2. La Niña:

a. Positive Aspects

• Often associated with increased rainfall in certain regions, which can be beneficial for agriculture, replenishing water resources, and reducing drought conditions.
• This can lead to cooler temperatures in some areas, which may be favorable for certain ecosystems and outdoor activities.

b. Negative Aspects

• Excessive rainfall during La Niña can also lead to floods, erosion, and Landslips; causing damage to infrastructure, affecting agriculture, and posing human safety risks.
• Warm water conditions affect negatively the marine ecosystems and thus the fisheries activities.

(Source: NOAA)

6. What is the Relationship Between El Niño-Southern Oscillation Cycle (ENSO) and Climate Change Phenomenon?

• The ENSO cycle is a phenomenon naturally occurring, however, under the strain of climate change, the heat index (also known as the apparent temperature or temperature felt by humans), in addition to violent natural episodes are outlined. According to the NOAA, El Niño is not caused by climate change.
• Indeed, oceans have the potential to absorb CO2 and heat; however, with the augmentation of their SSI, their ability to absorb atmospheric heat decreases. Even worse, they eject theirs into the atmosphere, thus worsening the atmosphere heat spread along the equator to further countries. Climate change has the potential to affect the frequency and intensity of El Niño and La Niña events, even though scientists are still skeptical about the quantification of this effect and its scope.
• Though the exact relationship between climate change and ENSO is still under scrutiny, some projections indicate that ongoing global warming could result in more frequent and severe El Niño and La Niña occurrences in the future.
• Additionally, climate change can amplify the impacts of those extreme events of the ENSO cycle on the weather and climate worldwide. For example, El Niño may lead to heightened heatwaves, droughts, and wildfires in certain regions, while La Niña can bring about more intense rainfall and flooding in other areas.

6. What is the Current Situation?

• The last El Niño year recorded was 2016 and the last La Niña was in the Northern Hemisphere between the years 2020 and 2022. According to the last update from the World Meteorological Organization (WMO) on 3 May 2023 in Geneva, the probability of the further development of El Niño is going up within the next months.
• The last prediction work led by the World Meteorological Organization (WMO) showed that El Niño is 90% likely to remain during the second half of 2023 against a likelihood of 10% of taking a dropping trend toward a neutral equilibrium state. While the current model guidance does not rule out the possibility of a strong event, the re-development of La Niña is practically ruled out until at least the end of 2023.
• As mentioned, the tropical Pacific is currently going through El Niño conditions, and the existence of higher-than-normal temperature anomalies beneath the surface of the eastern Pacific, along with a positive thermocline depth anomaly, has led to meaningful warming not only in the eastern Pacific but also extending westward. Nota Bene: A thermocline serves as the boundary separating the warmer mixed water at the water’s surface from the cooler deep water below.

7. The Impact of El Niño on the Environment, Economy, and Public Health:

• Those extreme weather events can significantly impact agriculture, water resources, ecosystems, and human communities. It is crucial to continue monitoring and studying the ENSO cycle and its interactions with climate change to reach a deeper understanding and prepare for potential global consequences. Governments, organizations, and individuals must take proactive measures to adapt to changing climate patterns and mitigate human activities contributing to climate change.
• El Niño can have significant impacts on the global economy, particularly in regions affected by its climate patterns. Some of the ways El Niño can impact the economy include:

7.1 . Agriculture and Fisheries:

• Shifts in weather patterns, lead to changes in precipitation and temperature. In some regions, it results in droughts, reduced water supply, and heat stress, which can damage crops, reduce agricultural yields, and increase food prices, thus generating accessibility to food issues.
• Disruptions in the warming of ocean waters marine ecosystems, lead to changes in fish migration patterns and reductions in fish stocks. This can negatively affect the fishing industry and the livelihoods of communities dependent on fishing.

7.2 . Resources:

a. Water:

• Reduced water availability due to rainfall patterns, impacts water supplies for drinking, irrigation, and industrial use, resulting in water scarcity.

(Source: UN Water)

b. Energies:

• Changes in temperature and precipitation can affect energy demand for heating and cooling, as well as hydroelectric power generation. It can also impact utilities’ operations, leading to higher operational costs and potential supply disruptions.

(Source: National Geographic)

7.3. Economy and Industry:

a. Infrastructure:

• It can intensify extreme weather events, such as heavy rainfall, floods, and landslides, prone to damaging infrastructure, disrupting transportation, and triggering significant economic losses.

b. Insurance and Financial Markets:

• The occurrence of severe weather events can result in augmenting the burden due to insurance claims, which can negatively impact insurance companies’ profitability and create crushes in the financial markets.
• Health insurance income can be affected in case of the emergence of ENSO-related health conditions.
• Reduced productivity in sectors like agriculture and outdoor labor can also impact overall economic output.

c. Trade and Supply Chains:

• El Niño’s effects on agricultural production and fisheries can cause disruptions in global supply chains and the trade of items, thus, influencing both prices and the availability of goods and commodities.

7.4. Public health:

• Impacts on weather conditions can have repercussions on public health, including the potential spread of diseases and heat-related illnesses such as plague and malaria.
• Some of the health consequences recorded by the WHO are:

- Injuries and fatalities

- Vector-driven diseases

- Diseases from contaminated water

- Food insecurities and thus malnutrition

- Mental health issues and heat stress

- Respiratory diseases

- Hard access to healthcare facilities and service

Therefore, governments, businesses, and communities should implement resiliency strategies to cope with the potential effects of this climate phenomenon.

8. How to avoid/cope with the impacts of El Niño?

Unlike climate change mainly induced by human activities, El Niño and La Niña are natural climate patterns, and humans have no direct control over their initiation, intensity, or period. It is rather about Managing than avoiding, and adaptive solutions are similar to those handled for climate change.

• Early Warning Systems, alimented by weather forecasts and meteorological agencies facilitate preparing for potential impacts beforehand within populations.
• Effective water management strategies for agriculture and households support saving water during dry periods and managing potential drought conditions.
• Climate-resilient agricultural strategies such as crop diversification, embracing drought-resistant crops, and adjusting planting schedules according to expected weather patterns can be achieved.
• Disaster Preparedness and Infrastructure Resilience for extreme weather events such as floods and storms, along with investing in resilient infrastructure able to withstand sharp weather conditions.
• Health Precautions and awareness of potential health risks associated with El Niño, like heat-related illnesses and take prevention measures.
• Conservation and Reforestation efforts aim to protect natural ecosystems, especially forests, which play a crucial role in climate regulation and mitigating extreme weather impacts.
• Sustainability corporate education/investment towards a Net Zero target, portfolio decarbonization, CO2 emissions reduction, and further mitigation steps of the effect of climate change.
• Community Awareness initiatives educate people about El Niño’s impacts and adaptation measures, fostering a shared sense of responsibility. Addressing underlying factors contributing to climate change, through Climate Change Mitigation, is essential as El Niño impacts can amplify the effects of global warming.
• Scientific research promotion to study, monitor, and forecast the ENSO oscillations in addition to its correlations to exiting and potentially supervening natural phenomena/disasters.

While these measures can assist in reducing the impacts of El Niño, currently occurring and which effects are highly perceived, they may not entirely prevent its effects. Therefore, building resilience and adapting to changing climate patterns and the Urban heat island effect (which refers to a localized warming wave phenomenon observed in cities temperatures compared to the rural regions due to the agglomeration of buildings and infrastructures) remain crucial in confronting the challenges imposed by El Niño and other climate-related events, and the potential associated phenomena to be depicted by scientific research.

Remark: The main resources used for the creation of this content are NOAA, NASA, WHO, UN, and ESA.