History of El Niño–Southern Oscillation in Timeline

El Niño–Southern Oscillation (ENSO) is a climate phenomenon characterized by irregular but somewhat cyclical variations in winds and sea surface temperatures over the tropical Pacific Ocean. ENSO significantly impacts the climate of tropical and subtropical regions, with teleconnections influencing weather patterns in higher latitudes. The phenomenon involves two phases: El Niño (warming) and La Niña (cooling), each typically lasting a year and occurring every 2-7 years with varying intensity. El Niño is associated with high air pressure over the western Pacific and Indian Ocean, while La Niña exhibits the opposite pattern. The Southern Oscillation refers to the coupled atmospheric changes.

1900: Start of El Niño Event Records

Records of El Niño events became more detailed and comprehensive starting around 1900.

1900: ENSO Events in Australia

Since 1900, Australia has experienced 28 El Niño and 19 La Niña events, demonstrating the significant influence of ENSO on the country's climate.

1904: Norman Lockyer's Observation

In 1904, Norman Lockyer corroborated Charles Todd's earlier suggestion, observing that droughts in India and Australia often coincided, hinting at a possible link with the El Niño phenomenon.

1907: Flooding in Beni Department, Bolivia

In 1907, La Niña conditions brought higher than normal rainfall in the central Andes, leading to catastrophic flooding on the Llanos de Mojos of Beni Department, Bolivia.

1919: Victor Eguiguren's Contribution

Although Victor Eguiguren passed away in 1919, his 1894 report linking El Niño with flooding marked an early recognition of the phenomenon's broader impact.

1921: Flooding in Beni Department, Bolivia

The Llanos de Mojos of Beni Department, Bolivia, experienced severe flooding in 1921 due to heavy rainfall in the central Andes, a consequence of the La Niña phase.

1924: Coining of "Southern Oscillation"

Gilbert Walker introduced the term "Southern Oscillation" in 1924, marking a significant step in understanding the atmospheric component of the El Niño phenomenon.

1925: Major El Niño Event Recorded

A major El Niño event was recorded in 1925-1926, contributing to the historical understanding of these events.

1928: Flooding in Beni Department, Bolivia

The year 1928 saw another instance of La Niña-induced heavy rainfall in the central Andes causing devastating floods on the Llanos de Mojos in Beni Department, Bolivia.

1929: Flooding in Beni Department, Bolivia

In 1929, the Llanos de Mojos region of Beni Department, Bolivia, faced catastrophic flooding due to the intense rainfall in the central Andes caused by the La Niña phenomenon.

1931: Flooding in Beni Department, Bolivia

The La Niña phase in 1931 triggered excessive rainfall in the central Andes, resulting in another instance of disastrous flooding in the Llanos de Mojos area of Beni Department, Bolivia.

1942: La Niña's Impact on Baja California's Plants

Between 1942 and 1957, La Niña's impact caused isotope changes in the plants of Baja California. This observation provided valuable data for scientists studying La Niña's effects.

1949: Creation of the Equatorial Southern Oscillation Index (EQSOI)

A new index, the Equatorial Southern Oscillation Index (EQSOI), was created in 1949 to address the limitations of the Southern Oscillation Index. This new index utilizes data from two regions centered on the Equator, one over Indonesia and the other over the equatorial Pacific near South America, providing a more accurate reflection of ENSO conditions.

1950: Strong La Niña Costera Event

A strong La Niña Costera event, a counterpart to El Niño Costero, occurred in 1950.

1950: ENSO and Civil Conflicts

Analysis of data from 1950 to 2004 by scientists at The Earth Institute of Columbia University suggests a potential link between ENSO and civil conflicts.

1950: ENSO Impact Observations

Observations of ENSO events since 1950 revealed that their impacts vary depending on the time of year. While some effects are expected, their occurrence is not guaranteed.

1954: Strong La Niña Costera Event

A strong La Niña Costera event occurred in 1954-1956.

1957: Strong El Niño Costero Event

A strong El Niño Costero event, a distinct type of El Niño with localized impacts, occurred in 1957.

1957: "Modoki" El Niño Event

An El Niño "Modoki" event occurred in 1957-1959, representing a distinct type of El Niño with its own characteristics.

1957: La Niña's Impact on Baja California's Plants

Between 1942 and 1957, La Niña's impact caused isotope changes in the plants of Baja California. This observation provided valuable data for scientists studying La Niña's effects.

1962: Strong La Niña Costera Event

A strong La Niña Costera event occurred in 1962.

1963: "Modoki" El Niño Event

An El Niño "Modoki" event occurred in 1963-1964.

1964: Strong La Niña Costera Event

A strong La Niña Costera event occurred in 1964.

1965: "Modoki" El Niño Event

An El Niño "Modoki" event occurred in 1965-1966.

1966: Strong La Niña Costera Event

A strong La Niña Costera event occurred in 1966.

1967: Strong La Niña Costera Event

A strong La Niña Costera event occurred in 1967-1968.

1968: "Modoki" El Niño Event

An El Niño "Modoki" event occurred in 1968-1970.

1968: Drought in Singapore

Singapore experienced its second driest February on record in 1968, with only 8.4 mm of rainfall, likely influenced by El Niño conditions.

1969: Bjerknes' Hypothesis and Theories on ENSO Phase Shifts

In 1969, Bjerknes further hypothesized that ENSO acts as a positive feedback system, where changes in the ocean or atmosphere reinforce changes in the other, exemplifying this with the weakening of trade winds during El Niño events. However, he acknowledged that other factors must be involved in shifting ENSO between phases, as the positive feedback loop alone would result in a perpetual state. This led to the development of theories categorized by either negative feedbacks reversing the abnormal state of the tropical Pacific, or irregular external phenomena driving the phase change.

1969: Bjerknes Feedback Mechanism Proposed

In 1969, Jacob Bjerknes identified a key mechanism of ENSO, now known as the Bjerknes feedback. This positive feedback loop describes how atmospheric changes influence sea temperatures, which in turn further impact atmospheric winds. For example, weaker trade winds lead to warmer surface waters moving eastward and reduced ocean upwelling, further weakening the Walker circulation and trade winds.

1970: Strong La Niña Costera Event

A strong La Niña Costera event occurred in 1970-1971.

1972: Major El Niño Event Recorded

Another major El Niño event occurred in 1972-1973, further demonstrating their significant and recurring nature.

1972: Peruvian Fisheries Collapse

In 1972, following the El Niño event, the Peruvian fisheries, which were once the world's largest, collapsed due to a combination of overfishing and the impacts of El Niño on anchoveta populations.

1972: ENSO and Fishery Crisis

The 1972–73 ENSO event led to a collapse in Peruvian and Chilean anchovy populations, causing a severe fishery crisis.

1973: La Niña Modoki Event

A La Niña Modoki event, a distinct type of La Niña, was observed in 1973-1974.

1975: La Niña Modoki Event

A La Niña Modoki event occurred in 1975-1976.

1975: Strong La Niña Costera Event

A strong La Niña Costera event occurred in 1975-1976.

1977: "Modoki" El Niño Event

An El Niño "Modoki" event occurred in 1977-1978.

1979: "Modoki" El Niño Event

An El Niño "Modoki" event occurred in 1979-1980.

1979: Limited Data Availability for ENSO Modoki Research

The discovery of ENSO Modoki and its potential link to global warming was hampered by the limited availability of comprehensive satellite data, which only became available from 1979 onward. This data limitation highlighted the need for further research to understand the relationship between ENSO Modoki, past El Niño episodes, and climate change.

1982: Strong El Niño Costero Event

A strong El Niño Costero event occurred in 1982-1983.

1982: Major El Niño Event Recorded

The 1982-1983 El Niño event, recognized as one of the strongest on record, showcased the potential for these events to cause widespread impacts.

1982: ENSO and Ecological Impacts

The 1982-83 ENSO event had devastating ecological consequences. It caused the likely extinction of two hydrocoral species in Panama and massive kelp bed mortality along 600 km of Chilean coastline.

1982: Fishery Impacts of the 1982-83 El Niño

The 1982-83 El Niño event had mixed impacts on fisheries. Some populations like jack mackerel and anchoveta decreased, while others, like scallops, increased. Hake moved down the continental slope following cooler water, while shrimp and sardines shifted southward.

1982: Impact of El Niño on Tropical Forests

The 1982-83 El Niño event led to prolonged droughts in tropical forests, causing widespread fires and significantly impacting forest structure and tree species composition in Amazonian and Bornean forests.

1982: Scientific Interest in El Niño

The significant 1982–83 El Niño event sparked a surge in scientific interest and research on the phenomenon and its global consequences.

1983: La Niña Modoki Event

A La Niña Modoki event occurred in 1983-1984.

1986: First Recorded Eastward-Moving Central Pacific El Niño

The year 1986 marked the first recorded instance of an El Niño event originating in the central Pacific and subsequently moving eastward, a pattern that would be observed in later years.

1988: La Niña Modoki Event

A La Niña Modoki event occurred in 1988-1989.

1990: Unusual El Niño Frequency

The period from 1990 to 1995 was exceptional due to an unusual frequency of El Niño events, raising questions and prompting further investigation into the phenomenon's dynamics.

1991: Central Pacific El Niño Event

A Central Pacific El Niño event occurred in 1991-1992.

1991: Chilean Fishing Restrictions

In 1991, the Chilean government implemented restrictions on fishing areas, impacting both self-employed fishermen and industrial fleets. This added another layer of complexity to the fishing industry already grappling with the effects of El Niño.

1994: Central Pacific El Niño Event

A Central Pacific El Niño event occurred in 1994-1995.

1997: Strong El Niño Costero Event

A strong El Niño Costero event occurred in 1997-1998.

1997: Strong El Niño Events Recorded

Another exceptionally strong El Niño event took place in 1997-98, further solidifying the understanding of their significant impact.

1997: El Niño and Epidemic Diseases

The 1997-98 El Niño event was linked to a severe outbreak of Rift Valley fever in northeastern Kenya and southern Somalia after the regions experienced extreme rainfall. This event highlighted the correlation between extreme weather conditions caused by El Niño and the increased risk of mosquito-transmitted diseases.

1997: Impact of El Niño on Tropical Forests

The 1997-98 El Niño event, like the one in 1982-83, resulted in extensive droughts and fires in Amazonian and Bornean forests, further demonstrating the significant impact of El Niño on these ecosystems.

1997: Global Mass Coral Bleaching Events

The 1997–98 ENSO event resulted in a global mass coral bleaching event, with 75-99% losses of live coral recorded worldwide, highlighting the devastating impact of ENSO on these fragile ecosystems.

1997: First Large-Scale Coral Bleaching Event

The Pacific Marine Environmental Laboratory attributed the first large-scale coral bleaching event to the warming waters caused by the 1997-98 El Niño event.

1998: La Niña Modoki Event

A La Niña Modoki event occurred in 1998-1999.

1998: Intense El Niño and Coral Bleaching

An exceptionally intense El Niño event in 1998, warming air temperatures by 1.5 °C, caused widespread coral bleaching, with an estimated 16% of the world's reef systems dying, highlighting the devastating impact of such events.

1998: First Large-Scale Coral Bleaching Event

The first large-scale coral bleaching event, attributed to the 1997-98 El Niño, highlighted the devastating effects of warming waters on coral reefs.

2000: La Niña Modoki Event

A La Niña Modoki event occurred in 2000-2001.

2000: El Niño Monitoring in the 21st Century

Since 2000, the monitoring of El Niño events has continued, revealing a pattern of occurrences throughout the early 21st century.

2002: Central Pacific El Niño Event

A Central Pacific El Niño event occurred in 2002-2003.

2002: El Niño Event

An El Niño event was observed in 2002-2003.

2004: Central Pacific El Niño Event

A Central Pacific El Niño event occurred in 2004-2005.

2004: El Niño Event

An El Niño event was observed in 2004-2005.

2004: ENSO and Civil Conflicts

Research concluding in 2004 suggested that ENSO may have played a role in 21% of all civil conflicts since 1950. The study found that the risk of annual civil conflict doubled in countries affected by El Niño compared to La Niña years.

2005: Drought in Singapore

Singapore experienced its second driest February on record in 2005, with only 8.4 mm of rainfall, likely influenced by El Niño conditions.

2006: El Niño Event

An El Niño event was observed in 2006-2007.

2006: Potential Central Pacific El Niño Event

The El Niño event of 2006-2007 is considered by some sources to be a Central Pacific El Niño, though this classification is not universally agreed upon.

2007: La Niña and Eastern Canada Snowfall

The La Niña winter of 2007-2008 brought near-record-breaking snowfall to eastern Canada, demonstrating the significant impact of La Niña on North American winter weather.

March 2008: La Niña Impacts in Southeast Asia

In March 2008, La Niña caused a 2 °C drop in sea surface temperatures over Southeast Asia and brought heavy rains to the Philippines, Indonesia, and Malaysia, demonstrating its significant influence on regional weather patterns.

2008: La Niña Modoki Event

A La Niña Modoki event occurred in 2008-2009.

2008: La Niña and Eastern Canada Snowfall

The La Niña winter of 2007-2008 brought near-record-breaking snowfall to eastern Canada, demonstrating the significant impact of La Niña on North American winter weather.

2009: Central Pacific El Niño Event

A Central Pacific El Niño event occurred in 2009-2010.

2009: El Niño Event

An El Niño event was observed in 2009-2010.

2010: La Niña Modoki Event

A La Niña Modoki event occurred in 2010-2011.

2010: Drought in Singapore

Singapore experienced its driest February since records began in 1869 during the 2010 El Niño event. Only 6.3 mm of rain fell, highlighting the extreme drought conditions brought by El Niño.

2013: Strong La Niña Costera Event

A strong La Niña Costera event occurred in 2013.

2014: Major El Niño Event Recorded

A major El Niño event took place in 2014-2016, underscoring their recurring nature and potential for substantial global effects.

2014: Potential Central Pacific El Niño Event

Similar to the 2006-2007 event, the El Niño of 2014-2016 is also sometimes classified as a Central Pacific El Niño, though this remains a point of debate.

2014: Proposal of the South Pacific Meridional Mode (SPMM)

Zhang, Clement, and Di Nezio put forward the existence of the "South Pacific Meridional Mode" (SPMM) in 2014, drawing a parallel to the Northern Hemisphere's PMM and its influence on climate patterns.

2015: Strong El Niño Costero Event

A strong El Niño Costero event occurred in 2015-2016.

2015: Global Mass Coral Bleaching Events

Similar to the 1997-98 event, the 2015-16 ENSO event caused another global mass coral bleaching event, further emphasizing the vulnerability of coral reefs to these climatic events.

2015: Impact of El Niño on Tropical Forests

The 2015-16 El Niño caused severe droughts and fires in Amazonian and Bornean forests, leading to declines in insect populations, habitat-specialist bird species, and large-frugivorous mammals. Over 100 lowland butterfly species were temporarily wiped out at a burned forest site in Borneo.

2016: La Niña Modoki Event

A La Niña Modoki event occurred in 2016-2017.

2018: El Niño Event

An El Niño event was observed in 2018-2019.

2018: SPMM Peak Anomalies Timing

You and Furtado, in 2018, elaborated on the SPMM, suggesting that sea surface temperature anomalies peak during the austral summer, while wind anomalies peak during the austral winter.

2019: Cloud Radiative Feedbacks on SPMM

Middlemas et al., in 2019, associated cloud radiative feedbacks with counteracting the persistence of the SPMM, adding another layer to the understanding of this climate mode.

2019: Emerging Research on Climate Change and Extreme El Niño Events

Starting around 2019, new research began to emerge suggesting a link between climate change and an increased frequency of extreme El Niño events. This marked a shift from previous uncertainties surrounding the impact of climate change on the strength and duration of El Niño events, which had yielded conflicting findings.

2021: IPCC Sixth Assessment Report on ENSO and Climate Change

The 2021 IPCC Sixth Assessment Report highlighted the uncertain future trends of ENSO due to climate change, noting that while the impacts of droughts and floods are likely to be exacerbated, there is no consensus on the exact nature of these changes. The report did state that "in the long term, it is very likely that the precipitation variance related to El Niño–Southern Oscillation will increase", and that "it is very likely that rainfall variability related to changes in the strength and spatial extent of ENSO teleconnections will lead to significant changes at regional scale".

2021: IPCC Sixth Assessment Report Summarizes ENSO Research

The 2021 IPCC Sixth Assessment Report provided a comprehensive overview of the current understanding of ENSO's future. The report summarized the latest research findings and highlighted key areas of uncertainty regarding the impact of climate change on ENSO.

October 2022: El Niño's Impact on Seasonally Dry Tropical Forests

A study published in October 2022 revealed that El Niño-induced drought increased seedling mortality in seasonally dry tropical forests in Thailand, indicating potential long-term impacts on these ecosystems.

2022: La Niña Impacts in Oregon

In the spring of 2022, La Niña brought above-average precipitation and below-average temperatures to Oregon. April was one of the wettest months on record, highlighting the influence of La Niña on regional weather patterns.

2023: Major El Niño Event Recorded

A major El Niño event was observed in 2023-2024.

2023: El Niño Event

An El Niño event was observed in 2023-2024.

2023: 2023 El Niño Event in Australia

Australia declared an El Niño event on September 17, 2023, marking the latest in a series of ENSO events that significantly impact the country's climate.

2023: CSIRO Study on Climate Change and El Niño/La Niña Likelihood

In 2023, a study by CSIRO researchers found that climate change may have doubled the likelihood of strong El Niño events and increased the likelihood of strong La Niña events by nine times. This study, which identified a consensus across various models and experiments, added weight to the growing body of evidence linking climate change to more frequent and severe El Niño and La Niña events.