What is El Niño and Why does it Matter?

The world is already experiencing hotter temperatures year on year thanks to climate change, but with 2023 marking the beginning of a new El Niño cycle, temperatures could smash records across the globe. 

👉 In this article we’ll explore what El Niño is, how it is impacted by climate change, and what it means for countries across the globe. 

The Earth is said to be in a period of El Niño when sea surface temperatures in the eastern Pacific rise 0.5 degrees celsius above the long-term average. The effects are most felt in the tropical eastern Pacific region where weather will also be hotter than average. However, impacts are not just limited to this corner of the world - global weather patterns are also influenced.

El Niño is part of a 3 to 7 year cycle (5 years on average) known as El Niño Southern Oscillation (ENSO), whereby the Earth’s climate system fluctuates between a period of El Niño and La Niña. 

💡Southern Oscillation is the term for atmospheric pressure changes between the east and west tropical Pacific that accompany the El Niño and La Niña oceanic changes. 

La Niña describes the corresponding side of the fluctuation and is a period of cooler than average sea surface temperature in the equatorial Pacific. Sea temperatures will be between 3 and 5 degrees celsius lower than average, bringing cooler and drier weather to the tropical eastern Pacific region.

Both El Niño and La Niña tend to develop during March to June, reaching the height of their effects around December to April, then weakening off again in between May and July. 

👉 There are also periods where the cycle is said to be more neural - ie. the temperature is closer to the long term average. In fact, half of all years are described as neutral.

When people hear about the warming effects of El Niño they often assume that it has something to do with climate change. However, the El Niño Southern Oscillation cycle is a natural process that has been ongoing for thousands and thousands of years.

ENSO is essentially a periodic fluctuation in sea surface temperature and air pressure of the overlying atmosphere across the equatorial Pacific region. Changes to the ocean surface temperature affect tropical rainfall patterns and atmospheric winds over the Pacific ocean, which in turn affects the ocean temperatures and currents.

Neutral state

Under normal conditions (ie. during neutral periods of the cycle) the trade winds blow in a westerly direction across the Pacific. These winds cause the cooler water in the eastern Pacific to flow westwards along the equator where the sun heats the temperature of the water. The result is that the sea surface temperature in the western Pacific region is warmer than that of the eastern Pacific by around 8 to 10 degrees celsius. The warmer sea water causes the typically hotter, wet, low-pressure weather that characterize the western Pacific region.

El Niño

During an El Niño state we see a rise in air pressure over the western Pacific region (ie. the Indian Ocean, Indonesia, and Australia). Trade winds in the south Pacific region weaken or shift in an easterly direction, thereby moving the typically warmer waters of the western Pacific region eastwards. This results in higher air surface pressure in the western Pacific region and hotter, wetter weather in the eastern Pacific.

La Niña

La Niña is the colder counterpart of El Niño. It occurs when strong winds blow the warmer surface water away from the eastern Pacific region, further west than normal. Cooler deep ocean water rises to the surface due to an increase in upwelling along the western coast of South America, this causes the sea surface temperature in the eastern Pacific to drop by 3 to 5 degrees below average.

👉 Even though the phenomenon occurs in the Pacific region, El Niño and La Niña impact weather patterns across the globe.

El Niño and La Niña affect global weather patterns, however, not all regions are impacted in the same way. What’s more, is that the impacts of El Niño and La Niña are never the same - their effects depend on the intensity of the event, the time of year that they develop and other climate patterns that are taking place. It’s a very complex process to study, and one that is difficult to predict!

El Niño

During El Niño, trade winds weaken and warm water is pushed further east towards the coast of the Americas. The result is that regions in southern South America, the southern United States, the Horn of Africa, and central Asia experience increased rainfall. At the same time, Australia, Indonesia, and parts of southern Asia experience dry weather and increased incidences of droughts and wildfires. 

👉 The warmer waters in the eastern Pacific region caused by El Niño can also drive hurricanes in the central and eastern Pacific Ocean regions, while decreasing the risk of hurricanes in the Atlantic basin.

La Niña

La Niña will typically have the opposite effect on global weather patterns, with wet conditions in Australia, southeast Asia, southeastern Africa, and northern Brazil. Drier than normal conditions can usually be observed in parts of South America (particularly in the south of the continent) and the Gulf Coast of the United States. Over the winter months, we can also expect to see colder and stormier conditions across North America. 

👉 The upwelling caused by La Niña brings nutrient-rich, cold waters to the surface. This increases the numbers of fish in the region, which is good news for fishermen operating in the waters of western South America.

Even though El Niño and La Niña have been occurring for thousands of years, and are not a phenomenon that is caused by climate change, some experts believe that global warming is actually influencing the El Niño Southern Oscillation cycle. 

👉 Since the 1970’s we’ve seen more frequent and longer lasting El Niño cycles, leading some scientists to hypothesis that warmer global sea surface temperatures caused by climate change are resulting in an increase in El Niño periods. However, this is an area of ongoing research and it’s not entirely clear whether or not the El Niño Southern Oscillation cycle is impacted by global warming. 

What is certain however, is that the combination of both climate change and El Niño has the potential to exacerbate extreme weather conditions. 

Scientists predict that the next El Niño event could result in heavy rains across the south of North America, hotter and more intense heatwaves in Europe, and drought in countries such as Brazil and Indonesia.

In June the US National Oceanic and Atmospheric Administration announced that a new El Niño cycle is currently underway. 

Given that El Niño periods typically result in warmer temperatures, the cycle could have catastrophic effects ranging from searing heat waves to more intense storms.

The first regions to feel the first effects of El Niño are most likely to be countries in the Pacific, regions of the west coast of America, Japan, Australia, and New Zealand: 

• Indonesia and Australia already experience devastating wildfires, and sadly this risk will be heightened by the hotter and drier weather that they can expect to experience thanks to El Niño. 
• East Africa will also be at an increased risk of heavy rain and flooding.
• The Pacific region is likely to suffer from more tropical cyclones. 

However, the impact of El Niño is not limited to countries in the Pacific region - we can also expect to experience the effects of El Niño in Europe and North America. Northern Europe for example may experience a colder winter and hotter than normal temperatures in the summer. While southern Europe may experience more rain. 

Similarly in the US, the north of the country can expect colder temperatures in the winter and a hotter summer, whereas the weather is likely to be wetter than normal in the south.

However, it should be noted that the temperature spike caused by El Niño is temporary only and will not affect long-term climate targets. Still, the impacts in the short term can be very damaging.

El Niño will increase incidences of extreme weather and push global temperatures higher - this has the potential to create devastating effects, with food systems, infrastructure, ecosystems, and human health all impacted.

For example, one of the effects of El Niño is that the nutrient rich cooler water does not rise as easily on the western coast of South America - this reduces the number of fish and marine life in the region, which can affect the livelihoods of fishing communities. 

Extreme weather events such as drought and flooding can severely affect food security - it's estimated that during the El Niño event of 2025-2016 as many as 60 million people suffered from food insecurity as a direct result. If we experience an intense El Niño cycle this could become a significant problem again. 

The potential rise in global temperature is also bad news for delicate ecosystems such as the Earth’s coral reefs. If global temperatures breach the 1.5 degrees Celsius threshold, coral reefs could decline by as much as 70 to 90%. Even a brief passing of this temperature threshold could have devastating effects on these delicate ecosystems.

We're already beginning to see the harmful impacts of El Niño in South America. Chile recently suffered the deadly impacts of a large-scale forest fire brought about by increased temperatures and a prolonged period of drought in the country. Unfortunately, El Niño's impact on ocean temperatures in the Pacific region made this event more likely. A recent study found that "El Niño and climate-fuelled droughts and heat waves boost the local fire risk and have decisively contributed to the intense fire activity recently seen in Central Chile." Unfortunately, the combination of climate change and El Niño makes similarly devastating weather events more likely across the globe.

Even though the science is not clear on whether or not climate change is impacting the El Niño Southern Oscillation cycle, what is clear is that El Niño and La Niña have the potential to exacerbate the impacts of global warming. 

We’re now heading into another El Niño period, and even though the most extreme effects are not expected to be felt until 2024, the combination of climate change and El Niño means that we are entering uncharted territory. 

This is why it’s so important to understand and study the El Niño Southern Oscillation cycle. It is essential for predictive modeling that can help us to anticipate and therefore mitigate or adapt to the worst effects of these cycles.

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