El Niño is a climate pattern that describes the unusual warming of surface waters in the eastern tropical Pacific Ocean. El Nino is the “warm phase” of a larger phenomenon called the El Nino-Southern Oscillation (ENSO). La Nina, the “cool phase” of ENSO, is a pattern that describes the unusual cooling of the region’s surface waters. El Niño and La Niña are considered the ocean part of ENSO, while the Southern Oscillation is its atmospheric changes.
El Niño has an impact on ocean temperatures, the speed and strength of ocean currents, the health of coastal fisheries, and local weather from Australia to South America and beyond. El Niño events occur irregularly at two- to seven-year intervals. However, El Niño is not a regular cycle, or predictable in the sense that ocean tides are.
El Niño was recognized by fishers off the coast of Peru as the appearance of unusually warm water. We have no real record of what indigenous Peruvians called the phenomenon, but Spanish immigrants called it El Niño, meaning “the little boy” in Spanish. When capitalized, El Niño means the Christ Child, and was used because the phenomenon often arrived around Christmas. El Niño soon came to describe irregular and intense climate changes rather than just the warming of coastal surface waters.
Led by the work of Sir Gilbert Walker in the 1930s, climatologists determined that El Niño occurs simultaneously with the Southern Oscillation. The Southern Oscillation is a change in air pressure over the tropical Pacific Ocean. When coastal waters become warmer in the eastern tropical Pacific (El Niño), the atmospheric pressure above the ocean decreases. Climatologists define these linked phenomena as El Niño-Southern Oscillation (ENSO). Today, most scientists use the terms El Niño and ENSO interchangeably.
Scientists use the Oceanic Nino Index (ONI) to measure deviations from normal sea surface temperatures. El Niño events are indicated by sea surface temperature increases of more than 0.9° Fahrenheit for at least five successive three-month seasons. The intensity of El Niño events varies from weak temperature increases (about 4–5° F) with only moderate local effects on weather and climate to very strong increases (14–18° F) associated with worldwide climatic changes.
In order to understand the development of El Niño, it’s important to be familiar with non-El Niño conditions in the Pacific Ocean. Normally, strong trade winds blow westward across the tropical Pacific, the region of the Pacific Ocean located between the Tropic of Cancer and the Tropic of Capricorn. These winds push warm surface water towards the western Pacific, where it borders Asia and Australia.
Due to the warm trade winds, the sea surface is normally about .5 meter (1.5 feet) higher and 45° F warmer in Indonesia than Ecuador. The westward movement of warmer waters causes cooler waters to rise up towards the surface on the coasts of Ecuador, Peru, and Chile. This process is known as upwelling.
Upwelling elevates cold, nutrient-rich water to the euphotic zone, the upper layer of the ocean. Nutrients in the cold water include nitrates and phosphates. Tiny organisms called phytoplankton use them for photosynthesis, the process that creates chemical energy from sunlight. Other organisms, such as clams, eat the plankton, while predators like fish or marine mammals prey on clams.
Upwelling provides food for a wide variety of marine life, including most major fisheries. Fishing is one of the primary industries of Peru, Ecuador, and Chile. Some of the fisheries include anchovy, sardine, mackerel, shrimp, tuna, and hake.
The upwelling process also influences global climate. The warm ocean temperature in the western Pacific contributes to increased rainfall around the islands of Indonesia and New Guinea. The air influenced by the cool eastern Pacific, along the coast of South America, remains relatively dry.
El Niño Events
El Niño events are defined by their wide-ranging teleconnections. Teleconnections are large-scale, long-lasting climate anomalies or patterns that are related to each other and can affect much of the globe.
During an El Niño event, westward-blowing trade winds weaken along the Equator. These changes in air pressure and wind speed cause warm surface water to move eastward along the Equator, from the western Pacific to the coast of northern South America.
These warm surface waters deepen the thermocline, the level of ocean depth that separates warm surface water from the colder water below. During an El Niño event, the thermocline can dip as far as 152 meters (500 feet).
This thick layer of warm water does not allow normal upwelling to occur. Without an upwelling of nutrient-rich cold water, the euphotic zone of the eastern Pacific can no longer support its normally productive coastal ecosystem. Fish populations die or migrate. El Niño has a devastating impact on Ecuadorian and Peruvian economies.
El Niño also produces widespread and sometimes severe changes in the climate. Convection above warmer surface waters bring increased precipitation. Rainfall increases drastically in Ecuador and northern Peru, contributing to coastal flooding and erosion. Rains and floods may destroy homes, schools, hospitals, and businesses. They also limit transportation and destroy crops.
As El Niño brings rain to South America, it brings droughts to Indonesia and Australia. These droughts threaten the region’s water supplies, as reservoirs dry and rivers carry less water. Agriculture, which depends on water for irrigation, is threatened.
Stronger El Niño events also disrupt global atmospheric circulation. Global atmospheric circulation is the large-scale movement of air that helps distribute thermal energy (heat) across the surface of the Earth. The eastward movement of oceanic and atmospheric heat sources cause unusually severe winter weather at the higher latitudes of North and South America. Regions as far north as the U.S. states of California and Washington may experience longer, colder winters because of El Niño.
El Niño events of 1982-83 and 1997-98 were the most intense of the 20th century. During the 1982-83 event, sea surface temperatures in the eastern tropical Pacific were 9-18° F above normal. These strong temperature increases caused severe climatic changes: Australia experienced harsh drought conditions; typhoons occurred in Tahiti; and record rainfall and flooding hit central Chile. The west coast of North America was unusually stormy during the winter season, and fish catches were dramatically reduced from Chile to Alaska.
The El Niño event of 1997-98 was the first El Niño event to be scientifically monitored from beginning to end. The 1997-98 event produced drought conditions in Indonesia, Malaysia, and the Philippines. Peru experienced very heavy rains and severe flooding. In the United States, increased winter rainfall hit California, while the Midwest experienced record-breaking warm temperatures during a period known as “the year without a winter.”
El Niño-related disruption of global atmospheric circulation extends beyond Pacific Rim nations. Strong El Niño events contribute to weaker monsoons in India Southeast Asia. ENSO has even contributed to increased rainfall during the rainy season in sub-Saharan Africa.
Diseases thrive in communities devastated by natural hazards such as flood or drought. El Niño-related flooding is associated with increases in cholera, dengue, and malaria in some parts of the world, while drought can lead to wildfires that produce respiratory problems.
'Flavors' of El Niño
Variations of El Niño are referred to as “flavors.” The transition period of an El Niño event, for instance, is called a "Trans Niño." Trans Niño events occur at the onset and closing of an El Niño event. Trans Niño events often include increased tornado activity in the American Midwest.
Another "flavor" of El Niño is the El Niño Modoki, or Modoki Niño. Modoki is a Japanese word meaning "similar, but different." Modoki Niño, also called the Central Pacific Niño, is characterized by changes in sea-surface temperatures in the central, not eastern, Pacific. Some Modoki Niño events are distinct from traditional El Niño events, such as increased hurricane activity in the Atlantic and Gulf of Mexico. Many meteorologists are critical of the Modoki Niño, calling for more climate models to study the proposed phenomenon.
Monitoring El Niño
Scientists, governments, and non-governmental organizations (NGOs) collect data about El Niño using a number of technologies. The National Oceanic and Atmospheric Administration (NOAA), for instance, operates a network of scientific buoys. These buoys measure ocean and air temperatures, currents, winds, and humidity. The buoys are located at about 70 locations in the southern Pacific Ocean, from the Galapagos Islands to Australia.
Olympic El Niño
El Niño put a damper on the 2010 Winter Olympics in Vancouver, British Colombia, Canada. The weather pattern brought unseasonably warm weather to the normally chilly coastal town.
El Niño devastates western South American fisheries—and also fertilizer industries. The South American fertilizer industry is driven by the droppings of seabirds, whose population declines during El Niño events due to a reduction in their food source (fish).
In the Rings
Scientists are able to detect an El Niño event and its effects on the climate through a variety of technological and natural sciences. One of these natural sciences is dendrochronology, or the study of tree rings. Dendrochronologists study the rings of a tree in order to understand climatic conditions during specific time periods. Thin rings often indicate drier seasons while fatter rings indicate rainy seasons. Depending on where the tree is, scientists can see past El Niño events in trees that exhibit signs of much rainier or drier seasons that normal.
the art and science of cultivating land for growing crops (farming) or raising livestock (ranching).
alterations in the layer of air surrounding the Earth, such as an increase of pollution or humidity.
large-scale movement of air that helps distribute thermal energy (heat) on the surface of the Earth.
force per unit area exerted by the mass of the atmosphere as gravity pulls it to Earth.
floating object anchored to the bottom of a body of water. Buoys are often equipped with signals.
all weather conditions for a given location over a period of time.
person who studies long-term patterns in weather.
edge of land along the sea or other large body of water.
transfer of heat by the movement of the heated parts of a liquid or gas.
steady, predictable flow of fluid within a larger body of that fluid.
(singular: datum) information collected during a scientific study.
harmful condition of a body part or organ.
period of greatly reduced precipitation.
community and interactions of living and nonliving things in an area.
irregular, recurring weather system that features a warm, eastern-flowing ocean current in the eastern Pacific Ocean.
El Nino-Southern Oscillation (ENSO)
climate pattern in which coastal waters become warmer in the eastern tropical Pacific (El Nio), and atmospheric pressure decreases at the ocean surface in the western tropical Pacific (Southern Oscillation).
imaginary line around the Earth, another planet, or star running east-west, 0 degrees latitude.
act in which earth is worn away, often by water, wind, or ice.
upper zone of the ocean. This zone goes down to approximately 600 feet. Also called the epipelagic or sunlit zone.
industry or occupation of harvesting fish, either in the wild or through aquaculture.
overflow of a body of water onto land.
to predict, especially the weather.
amount of water vapor in the air.
tropical storm with wind speeds of at least 119 kilometers (74 miles) per hour. Hurricanes are the same thing as typhoons, but usually located in the Atlantic Ocean region.
time period between events or activities.
watering land, usually for agriculture, by artificial means.
weather system that includes cool ocean temperatures in the eastern Pacific Ocean.
distance north or south of the Equator, measured in degrees.
an animal that lives most of its life in the ocean but breathes air and gives birth to live young, such as whales and seals.
person who studies patterns and changes in Earth's atmosphere.
area of the United States consisting of the following states: Illinois, Indiana, Iowa, Kansas, Michigan, Minnesota, Missouri, Nebraska, North Dakota, Ohio, South Dakota, and Wisconsin.
to move from one place or activity to another.
to observe and record behavior or data.
seasonal change in the direction of the prevailing winds of a region. Monsoon usually refers to the winds of the Indian Ocean and South Asia, which often bring heavy rains.
National Oceanic and Atmospheric Administration (NOAA)
U.S. Department of Commerce agency whose mission is to "understand and predict changes in climate, weather, oceans, and coasts; to share that knowledge and information with others, and; to conserve and manage coastal and marine ecosystems and resources."
event in the physical environment that is destructive to human activity.
type of salt used as fertilizer. Excess nitrates can choke freshwater ecosystems.
substance an organism needs for energy, growth, and life.
Oceanic Nino Index
set of data used by scientists to measure the differences in normal sea surface temperatures.
an unusual act or occurrence.
type of salt used as fertilizer. Excess phosphates can choke freshwater ecosystems.
process by which plants turn water, sunlight, and carbon dioxide into water, oxygen, and simple sugars.
microscopic organism that lives in the ocean and can convert light energy to chemical energy through photosynthesis.
all forms in which water falls to Earth from the atmosphere.
animal that hunts other animals for food.
regular or able to be forecasted.
first or most important.
time of year when most of the rain in a region falls.
natural or man-made lake.
photographs of a planet taken by or from a satellite.
at the same time.
decrease in the air pressure over the tropical eastern and western Pacific Ocean, linked to El Nino.
widely spaced, large-scale, long-lasting climate anomalies or patterns that are related to each other and can affect much of the globe.
degree of hotness or coldness measured by a thermometer with a numerical scale.
heat, measured in joules or calories.
level or layer of a fluid depth where temperature changes more rapidly than the fluid either above or below it.
rise and fall of the ocean's waters, caused by the gravitational pull of the moon and sun.
a violently rotating column of air that forms at the bottom of a cloud and touches the ground.
winds that blow toward the Equator, from northeast to southwest in the Northern Hemisphere and from southeast to northwest in the Southern Hemisphere.
to pass along information or communicate.
movement of people or goods from one place to another.
existing in the tropics, the latitudes between the Tropic of Cancer in the north and the Tropic of Capricorn in the south.
tropical storm with wind speeds of at least 74 miles (119 kilometers) per hour. Typhoons are the same thing as hurricanes, but usually located in the Pacific or Indian Ocean region.
process in which cold, nutrient-rich water from the bottom of an ocean basin or lake is brought to the surface due to atmospheric effects such as the Coriolis force or wind.
to make visual.
state of the atmosphere, including temperature, atmospheric pressure, wind, humidity, precipitation, and cloudiness.