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What Is the Difference Between El Niño and La Niña?
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Images of sea-surface height taken during the El Nino episodes of 1997 and 2015. Diagram of the equatorial Pacific Ocean showing El Nino conditions, with weak trade winds, increased rainfall over South America, increased convection, a deepened thermocline, and suppressed upwelling. Map of the tropical Pacific Ocean highlighting the four ENSO (El Niño-Southern Oscillation) regions: Niño 4, Niño 3.4, Niño 3, and Niño 1+2. The regions are marked as colored rectangles along the equator from near Australia to the coast of South America, illustrating key zones used to monitor El Niño and La Niña climate events. World map illustrating the generalized weather effects of El Nino from December through February. Regions are labeled and shaded to show conditions such as warm in parts of North America, Asia, and South America; wet in the southern United States and eastern South America; dry and warm in southern Africa and Southeast Asia; wet and cool in the northern United States; and wet and warm across central and eastern equatorial Pacific. World map illustrating the generalized weather effects of La Nina from December through February. The map highlights regions experiencing wet, dry, cool, or warm conditions, such as wet and cool in southeastern Africa and Australia, dry in equatorial Africa, cool in northern North America and parts of South America, and dry and cool across the central Pacific.
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Images of sea-surface height taken during the El Nino episodes of 1997 and 2015.
Images of sea-surface height taken during the El Niño episodes of 1997 and 2015, which help to compare the intensity and extent of warm water in the eastern tropical Pacific Ocean El Niño episodes are characterized by unusually warm ocean conditions along the tropical west coast of South America. These episodes, such as the 1997 and 2015 El Niño events depicted in the image, are associated with adverse effects on fishing, agriculture, and local weather from Ecuador to Chile and with far-field climatic anomalies in the equatorial Pacific and occasionally in Asia and North America.

What Is the Difference Between El Niño and La Niña?

Written by
John P. Rafferty
John P. Rafferty writes about Earth processes and the environment. He serves currently as the editor of Earth and life sciences, covering climatology, geology, zoology, and other topics that relate to...
John P. Rafferty
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Britannica Editors
Encyclopaedia Britannica's editors oversee subject areas in which they have extensive knowledge, whether from years of experience gained by working on that content or via study for an advanced degree....
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History

Every few years the phenomenon known as El Niño dominates the headlines. In other years its climatic alter ego La Niña appears, but what are they and what makes them different? Changes in the temperature of the equatorial Pacific Ocean and the climate effects that stem from those changes determine the difference between the two. El Niño and La Niña are different phases of the same system—the El Niño-Southern Oscillation (ENSO), a large-scale climate pattern whose oceanic and atmospheric characteristics occur in and above the east-central Pacific Ocean. El Niño and La Niña occur irregularly, every two to seven years more or less, and their appearance affects how air and ocean water circulate in the Pacific; they may also bring about strange, unseasonable weather thousands of miles away through their significant linkages, or teleconnections, with weather and climate processes in other parts of the world.

Map of the tropical Pacific Ocean highlighting the four ENSO (El Niño-Southern Oscillation) regions: Niño 4, Niño 3.4, Niño 3, and Niño 1+2. The regions are marked as colored rectangles along the equator from near Australia to the coast of South America, illustrating key zones used to monitor El Niño and La Niña climate events.
Monitoring regions for the El Niño-Southern Oscillation (ENSO)The important part of the equatorial Pacific Ocean is the Niño 3.4 region. The temperature departure from standing averages in this region determines whether El Niño or La Niña events will develop or whether ENSO neutral conditions continue.

El Niño is ENSO’s warm phase, and it appears when the surface temperature of an area of the central Pacific Ocean called the Niño 3.4 region is 0.5 °C (0.9 °F) or more above long-term average sea-surface temperatures for at least five successive overlapping three-month seasons. El Niño is associated with a weakening of the westward-moving trade winds near the Equator, which reduces the strength of the high-pressure cell found in the eastern South Pacific and the low-pressure cell found over Indonesia and northern Australia. During normal years (that is, those characterized by ENSO neutral conditions), drier conditions would prevail over western South America and wetter conditions over Indonesia and northern Australia. El Niño reverses these conditions, driving higher rainfall over western South America and lower rainfall over Indonesia and northern Australia.

Stronger trade winds help to move warm surface water away from the South American coast, which stimulates upwelling—that is, the movement of cold, dense, and nutrient-rich deep ocean water toward the surface. Weaker trade winds dampen upwelling. Since fewer nutrients are brought to the surface, plankton populations that depend on them decline, and the fishes that rely on the plankton may move away from traditional fishing grounds, which leaves fewer fish for small-scale and commercial fishing operations to harvest.

World map illustrating the generalized weather effects of El Nino from December through February. Regions are labeled and shaded to show conditions such as warm in parts of North America, Asia, and South America; wet in the southern United States and eastern South America; dry and warm in southern Africa and Southeast Asia; wet and cool in the northern United States; and wet and warm across central and eastern equatorial Pacific.
El Niño is associated with substantial changes to established weather patterns between December and FebruaryThe weather effects of El Niño include pronounced drought episodes in the western Pacific and southeastern Africa, warmer winter temperatures in parts of Asia and North America, and wetter conditions in central Africa, the deserts of North America, and especially along South America's Pacific coast.

In addition, during El Niño years when central Pacific sea-surface temperatures are substantially warmer than normal, reliable seasonal weather patterns can be upended in different parts of the world, resulting in unseasonably warm conditions between December and February in some parts of the Northern Hemisphere, warmer and drier conditions in southeastern Africa, and warmer and wetter conditions in parts of eastern South America. Strong El Niño events are associated with increased tropical cyclone activity in the North Pacific and reduced tropical cyclone activity in the North Atlantic.

World map illustrating the generalized weather effects of La Nina from December through February. The map highlights regions experiencing wet, dry, cool, or warm conditions, such as wet and cool in southeastern Africa and Australia, dry in equatorial Africa, cool in northern North America and parts of South America, and dry and cool across the central Pacific.
La Niña is associated with substantial changes to established weather patterns between December and FebruaryThe weather effects of La Niña include increased rainfall in Southeast Asia, northern Australia, and the maritime continent, cooler and drier conditions in the eastern equatorial Pacific, cooler conditions in parts of Africa, northeast Asia, and western North America, and increased precipitation in parts of several continents, especially in southeastern Africa and in the middle latitudes of North America.

La Niña, on the other hand, is ENSO’s cool phase, which is marked by central Pacific sea-surface temperatures that are cooler than normal—that is, when the sea-surface temperature of the Niño 3.4 region is 0.5 °C (0.9 °F) or more below long-term averages. La Niña events amplify westward-moving trade winds in the Pacific, which increases rainfall in Indonesia and northern Australia and strengthens the high-pressure cell near western South America. Stronger trade winds push warm water westward and drive northerly winds along South America’s Pacific coast. This process produces stronger upwelling, which, in turn, results in more plankton and fish near the surface and greater yields of anchovies, sardines, and other commercial fishes. Globally, La Niña brings cooler conditions to parts of Africa, northeast Asia, and western North America, with increased precipitation in parts of several continents, especially in southeastern Africa and in the middle latitudes of North America. La Niña has also been associated with lower crop yields in the Midwest and increased tropical cyclone activity in the North Atlantic.

John P. Rafferty