El Niño 2023 looks probable, with implications for human, national, and global security dimensions. (Update 5/16: El Niño is knocking on the door! Security community should be on alert!)

ENSO, or the El Niño-Southern Oscillation, is a periodic climate pattern involving changes in ocean temperatures and atmospheric pressure across the equatorial Pacific Ocean. This phenomenon consists of two phases, El Niño, which causes warmer-than-average sea surface temperatures, and La Niña, which results in cooler-than-average sea surface temperatures, influencing global weather patterns and affecting various regions differently. Currently, the Earth is in an ENSO-neutral phase, after two years of La Niña. 

NOAA tracks the strength of El Niño (and La Niña) phases by the Multivariate ENSO index, which combines several meteorological and oceanographic components (see below). This plot illustrates the nonuniformity of ENSO oscillations, both in timing and strength, which is why climatologists remark that every El Niño is different. According to NOAA, there is now a 62% chance that El Niño will develop between May and July 2023, with a 4 in 10 chance of a “strong” El Niño occurring. Such an El Niño is likely to increase global insecurity while intensifying many modes of ecological disruption.

The 2015-2016 extreme El Niño event, the strongest since 1997-98, had enormous impacts worldwide, arising partly from being supercharged by the background pattern of global warming (the average CO2 concentration in 2016 was 404.4ppm, an 11% increase over 2017’s level of 363.5ppm). Although the most recent El Niño in 2019 was relatively weak, parts of Southeast Asia experienced drought conditions that negatively impacted agriculture and water resources, and regions in South America faced heavy rainfall and flooding.

Some consequences from the 2015-16 El Niño event:

El Niño and Global Mean Temperatures

According to NASA records, the global mean temperature for 2015 was the highest in the instrumental record. That record stood for one year until 2016’s temperature dwarfed 2015. Currently, 2016 is the warmest year on record (although NASA datasets show that 2020 eventually tied 2016, even though the planet was then in La Niña conditions then). 

El Niño and Tropical Storm Activity

El Niño 2015-2016 significantly influenced tropical cyclone activity in both the Atlantic and Pacific Oceans. The Atlantic hurricane season was relatively quiet, arising from increased wind shear and a more stable atmosphere that tends to hinder the development and intensification of cyclones. However, the Eastern and Central Pacific experienced an increase in the number and intensity of tropical cyclones, some especially notable:

• Hurricane Patricia, a powerful storm that formed over the eastern Pacific Ocean in October 2015, was the strongest tropical cyclone ever recorded in the Western Hemisphere, with maximum sustained winds of 215 mph. Patricia caused catastrophic damage throughout Mexico, tearing roofs off buildings, uprooting trees, and flooding homes. Though only 10 people were killed due to the storm, thanks to early warnings, the economic losses for Mexico were estimated at $460 million.
• The South Pacific Island nations of Vanuatu, Tuvalu, and Kiribati were devastated by Cyclone Pam in March 2015. This powerful storm brought winds up to 155 miles per hour, causing widespread destruction and death. Many villages lost access to medical care, food, and water, and countless homes were destroyed. Cyclone Pam caused damage equivalent to more than 50 percent of the country’s GDP, according to the Vanuatu government.
• In February 2016, Cyclone Winston struck Fiji as a Category 5 tropical cyclone, causing extensive damage to the country from wind speeds up to 185 mph. The cyclone was particularly destructive due to its large size, slow movement, and extreme intensity as it made landfall. There were 44 fatalities, more than 24,000 homes destroyed, and more than 300,000 people affected by the cyclone, resulting in a major humanitarian crisis. Around $1.4 billion was also lost due to the cyclone’s economic damage. 
• Cyclone Fantala was an intense and long-lived tropical cyclone formed in the South Indian Ocean in April 2016. With maximum sustained winds of 175 mph, Fantala was one of the strongest cyclones ever recorded in the South Indian Ocean. Its track took it close to several islands, including Madagascar, Seychelles, and the outer islands of Mauritius. Although it did not make direct landfall on any major island, its powerful winds and heavy rainfall caused significant damage to infrastructure, agriculture, and coastal ecosystems.

El Niño and Droughts

Shifts in rainfall patterns and ocean circulation patterns can cause or exacerbate droughts in various regions worldwide. Some of the most affected areas for the 2015-2016 El Niño were:

• Southeast Asia: Countries like Indonesia, the Philippines, Malaysia, and Thailand experienced severe drought conditions during the 2015-2016 El Niño. In Indonesia, the drought led to a significant increase in forest fires, while in the Philippines, the agricultural sector was severely affected.
• Eastern and Southern Africa: Widespread drought conditions were experienced across parts of Eastern and Southern Africa, including countries like Ethiopia, Somalia, Zambia, Zimbabwe, and South Africa. The drought led to severe food shortages, water scarcity, and crop failure, affecting millions of people in the region.
• Central America and the Caribbean: Countries such as Guatemala, Honduras, El Salvador, and Haiti experienced drought conditions due to the El Niño event. This led to food shortages, water scarcity, and adverse agricultural impacts.
• Pacific Islands: Many Pacific Island nations, such as Papua New Guinea, Fiji, and the Solomon Islands, experienced droughts and water shortages during the 2015-2016 El Niño.
• Australia: Australia’s eastern and northern regions faced below-average rainfall and drought conditions, affecting agricultural production and causing severe water shortages in some areas.
• Brazil: The El Niño exacerbated the ongoing drought in parts of Brazil, particularly in the northeast and southeast regions, leading to water scarcity and negative impacts on agriculture and hydropower generation.
• India: The El Niño contributed to the deficit of monsoon rainfall in India, leading to drought conditions in several parts of the country. The drought also affected agricultural production, causing crop failures and water shortages.

El Niño and Disease and Illness

The 2015-2016 El Niño had various effects on patterns of disease and illness. Some of these impacts include:

• Vector-borne diseases: The El Niño event increased the risk of vector-borne diseases such as malaria, dengue fever, and Zika virus. The warmer temperatures and increased rainfall in certain regions provided favorable conditions for breeding mosquitoes, which are the primary vectors for these diseases. For example, the El Niño almost certainly contributed to the spread of the Zika virus in South and Central America by creating suitable conditions for the Aedes mosquito.
• Water-borne diseases: The heavy rainfall and flooding from El Niño in some regions increased the prevalence of water-borne diseases like cholera and leptospirosis. Contaminated water sources and poor sanitation led to outbreaks of these diseases in some areas.
• Respiratory infections: The drought conditions and wildfires caused by the 2015-2016 El Niño, particularly in Southeast Asia, increased air pollution due to smoke and haze. Negative impacts on air quality contributed to increased respiratory infections and other related health issues.
• Malnutrition and food-borne diseases: The droughts and crop failures led to food shortages and increased malnutrition in some regions, particularly Africa and Central America. Malnourished populations are more susceptible to various diseases, and food-borne illnesses can become more prevalent when food supplies are limited and people resort to potentially unsafe food.
• Rodent-borne diseases: The changes in weather patterns drive rodent population increases, which in turn tend to lead to a rise in rodent-borne diseases such as hantavirus and plague. For example, the warmer temperatures during the 2015-2016 El Niño contributed to increased rodent populations in some parts of the United States, increasing the risk of hantavirus transmission to humans.
• Heat-related illnesses: The unusually high temperatures during the 2015-2016 El Niño increased the risk of heat-related diseases, such as heatstroke and dehydration, particularly among vulnerable populations and those with pre-existing health conditions.

In light of the significant impacts of the 2015-2016 El Niño event on global weather patterns, droughts, disease transmission, and socioeconomic well-being, it is crucial to pay close attention to future El Niño events. The lessons learned from this event underscored the importance of early warning systems, preparedness plans, and coordinated responses to mitigate the effects of El Niño on vulnerable populations and ecosystems. The El Niño also serves as a stark reminder of the interdependence of our global community and the need for collaborative, proactive measures to safeguard our collective future in an era of increasing climate variability and change.

El Niño Effects (on Average) for Different Regions of the World (adapted from climate.gov)