El Niño Southern Oscillation (ENSO): What Is Its Role In Climate Change

by Julia Gaus

El Niño-Southern Oscillation (ENSO) is a natural climate pattern consisting of oceanic and atmospheric changes in the tropical Pacific [1]. While El Niño describes the oceanic pattern, Southern Oscillation refers to changes in the atmospheric pressure over the Pacific Ocean. 

The name stems from Spanish colonialists, who observed unusually warm ocean temperatures along the coast of Peru around Christmas time (El Niño means the Christ Child) [1]. 

ENSO is an example of natural climate variability as it swings between warm (El Niño) and cold (La Niña) phases and produces knock-on effects around the world [2]. Through these so-called ‘teleconnections’, ENSO can cause extreme weather events such as extended drought conditions that affect local economies. Climate change, a long-term change of the average climate, interacts with ENSO by supercharging temperature and rainfall variability [3].

This article briefly introduces the climate science behind ENSO before describing the worldwide climate and economic impact of a typical El Niño/La Niña year. It then discusses the growing scientific consensus about how climate change is affecting ENSO variability, and its consequences.

Between trade winds and upwelling: The geo-physics behind ENSO

Neutral state

ENSO occurs in the tropical Pacific between South America and Asia. Under normal or neutral conditions, strong winds – the trade winds – blow from East to West along the equator, pushing warm water from South America to Asia. As the warmer surface water is pushed westwards, cold nutrient-rich water rises up along the Western coast of Latin America; this is known as upwelling. As a result of the relatively cool water, the western coast of South America is dry in comparison to Indonesia and New Guinea, which receive more rainfall [2,4].

El Niño conditions

During El Niño the trade winds weaken, pushing less warm water towards the west and thus suppressing the upwelling of nutrient-rich cold water [2,4]. This change in cold and warm zones of the ocean also affects convection patterns, resulting in increased rainfall over the central or eastern Pacific while Indonesia and Australia receive below-average rainfall [1].

La Niña conditions

La Niña sees stronger than usual trade winds, pushing even more warm water from east to west. This results in more significant dry conditions over the central and eastern Pacific (South America) and increased rainfall in Indonesia [2,4]. 

ENSO does not follow a regular, predictable cycle, with El Niño events occurring irregularly in intervals of two to seven years and more frequently than La Niña events  [1].

Impacts of ENSO on weather around the world

Beyond the immediate impact on temperature and rainfall patterns across the Pacific, ENSO impacts weather patterns around the world through atmospheric teleconnections. 

Teleconnections are links between weather phenomena at different locations on Earth [5,6]. They often behave like a seesaw, meaning that as one area cools/dries, another warms/gets wetter and vice versa [5]. The stronger the El Niño / La Niña event, the stronger the teleconnections. Figure 3 shows a schematic of rainfall patterns under El Niño (left) and La Niña (right) conditions, illustrating the seesaw pattern. Both El Niño and La Niña events impact more than just the hydrological cycle. They can create extreme weather, affect ecosystems, agricultural productivity, and human communities [7].

How climate change affects ENSO and its socio-economic impacts

ENSO can act as an accelerator for global warming spikes. In 2023, a strong El Niño began that helped catapult 2023 and 2024 to be the warmest and second warmest years on record, beating 2016, which had also seen an El Niño event [8,9]. La Niña, on the other hand, can act as a dampener on average temperatures [10]. Nevertheless, neither effect counteracts the clear upward trend in global temperatures caused by human influence.

How, then, are increasing average global temperatures affecting ENSO?

The IPCC found in its sixth assessment report that there was no consensus among their models on the certainty of an increase in sea surface temperature variability. However, newer studies do predict an increase in temperature variability over the 21st century [3, 11, 12]. Correspondingly, an increase in rainfall variability is predicted [3]. 

These increasingly violent swings caused by the long-term forcing of climate change could exacerbate extreme weather events around the world. Studies show that El Niño events have caused significant socio-economic losses that could grow dramatically in a high-emissions scenario, whereas La Niña events tend to have only small positive impacts [7]. 

Even without a definite scientific consensus on how ENSO variability will evolve, its impact on weather patterns across the world means there is a clear need for a detailed monitoring of central Pacific Ocean temperatures to improve data and modelling, as well as for early warning systems and adaptation measures.

References:

[1] Climate.Gov Staff, 2016, El Niño and La Niña: Frequently asked questions, Climate.gov,  https://www.climate.gov/news-features/understanding-climate/el-ni%C3%B1o-and-la-ni%C3%B1a-frequently-asked-questions [accessed 25.05.25]
[2] National Geographic Society, nD, El Niño, National Geographic,  https://education.nationalgeographic.org/resource/el-nino/ [accessed 24.05.25]
[3] Cai et al, 2022, Increased ENSO sea surface temperature variability under four IPCC emission scenarios, nature climate change (Brief Communication), https://doi.org/10.1038/ s41558-022-01282-z
[4] NOAA, 2024, What are El Niño and La Niña? NOAA https://oceanservice.noaa.gov/facts/ninonina.html [accessed 25.05.25]
[5] Zavadoff & Arcodia, 2022, What are teleconnections? Connecting Earth’s climate patterns via global information superhighways, https://www.climate.gov/news-features/blogs/enso/what-are-teleconnections-connecting-earths-climate-patterns-global [accessed 25.05.25]
[6] National Weather Service, nD, ENSO Teleconnections, NOAA, https://www.weather.gov/fwd/teleconnections [accessed 25.05.25]
[7] Liu et al, 2023, Nonlinear El Niño impacts on the global economy under climate change, nature communications, https://doi.org/10.1038/s41467-023-41551-9 
[8] Bardan, 2025, Temperatures Rising: NASA Confirms 2024 Warmest Year on Record, NASA.gov, https://www.nasa.gov/news-release/temperatures-rising-nasa-confirms-2024-warmest-year-on-record/ [accessed 25.05.25]
[9] McGrath, 2023, El Niño planet-warming weather phase has begun, BBC,  https://www.bbc.com/news/science-environment-65839060 [accessed 25.05.25]
[10] Raghuraman et al., 2024, The 2023 global warming spike was driven by the El Niño–Southern Oscillation, Atmos. Chem. Phys., 24,   11275–11283, https://doi.org/10.5194/acp-24-11275-2024, 2024.
[11] McPhaden, 2023, Has climate change already affected ENSO? Climate.gov, https://www.climate.gov/news-features/blogs/enso/has-climate-change-already-affected-enso [accessed 25.05.25]
[12] Eyring et al., 2021, Human Influence on the Climate System. In Climate Change 2021: The Physical Science Basis. Contribution of Working Group I to the Sixth Assessment Report of the Intergovernmental Panel on Climate Change [Masson-Delmotte, V., P. Zhai, A. Pirani, S.L. Connors, C. Péan, S. Berger, N. Caud, Y. Chen, L. Goldfarb, M.I. Gomis, M. Huang, K. Leitzell, E. Lonnoy, J.B.R. Matthews, T.K. Maycock, T. Waterfield, O. Yelekçi, R. Yu, and B. Zhou (eds.)]. Cambridge University Press, Cambridge, United Kingdom and New York, NY, USA, pp. 423–552, doi: 10.1017/9781009157896.005.