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El Niņo: Cycle B

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1). El Niño is a warming of the Pacific Ocean between South America and the Date Line, centered directly on the Equator, and typically extending several degrees of latitude to either side of the equator.

2). La Niña is essentially the opposite of El Niño. La Niña exists when cooler than usual ocean temperatures occur on the equator between South America and the Date Line. The name La Niña ("the girl child") was coined to deliberately represent the opposite of El Niño ("the boy child").

3). Among El Niño's consequences are increased rainfall across the southern tier of the US and in Peru, which has caused destructive flooding, and drought in the West Pacific, sometimes associated with devastating brush fires in Australia.

4). In normal, non-El Niño conditions, the trade winds blow towards the west across the tropical Pacific. These winds pile up warm surface water in the west Pacific, so that the sea surface is about 1/2 meter higher at Indonesia than at Ecuador.

5). During El Niño, the trade winds relax in the central and western Pacific leading to a depression of the thermocline in the eastern Pacific, and an elevation of the thermocline in the west.


Scenario: El Niño, Spanish for the "Christ child," was originally the name used by fishermen to describe a warming of the Pacific Ocean off the coast of Peru that normally takes place around Christmas time. This warming occurs almost every year and lasts a few weeks. In the relatively recent past, however, scientists have discovered this warming can occasionally last for many months, sometimes even longer than a year, and extend westward along the Equator. Today, when we speak of El Niño, we are usually referring to this longer-term event.

El Niño and its opposite phenomenon -- La Niña -- are part of a cycle of repeated warming and cooling of the ocean surface along the Equator in the central and eastern Pacific. The cycle is known as the El Niño Southern Oscillation (ENSO). El Niño refers to the warm phase of the oscillation and La Nina refers to the cool phase. The Southern Oscillation refers to the fluctuation in pressure above the equatorial eastern and western Pacific. During an El Niño, pressure falls in the east and rises in the west. Since air tends to flow from high pressure toward low pressure, this causes winds that normally blow from east to west across the equator to slow down or even reverse direction. The opposite is true during La Niña, when east-to-west winds increase in strength.

Each of these phases influences weather patterns worldwide and results in changes in rainfall that can alter vegetation patterns. El Niño's impacts include changes in global precipitation that sometimes contribute to flooding or drought. Although scientists have a general idea of the regional weather changes that are typically associated with an El Niño, there are many exceptions to the long-term averages. When an El Niño is weak or moderate, it is especially difficult to predict its impacts. For example, the Los Angeles area normally has above-normal rainfall during weak to moderate El Niños, but during the El Niño of 2006-2007, the area experienced its driest year (July 2006-June 2007) on record.

El Niño has also been linked to: disease in South America, increased atmospheric carbon dioxide and methane from fires, harm to coral reefs, an absence of major hurricanes in the North Atlantic, a link to sea ice changes in Antarctica, and economic implications for the United States.


Author: Bob Myers, IGES



Date: 12/6/2012


Scenario Images

El Nino Southern Oscillation
El Nino is an oscillation of the ocean-atmosphere system in the tropical Pacific having significant consequences for weather around the globe. Among these effects are increased rainfall across the southern portion of the US and in Peru. El Nino, also referred to as ENSO (El Nino Southern Oscillation)has caused destructive flooding, and drought in the West Pacific; it is sometimes associated with devastating brush fires in Australia. Observations of conditions in the tropical Pacific are considered essential for the prediction of short term (a few months to 1 year) climate variations. Go here to compare normal, El Nino and La Nina conditions. Image courtesy of NOAA



  • Science
    National Science Education Standards - Science Content Standards The science content standards outline what students should know, understand, and be able to do in the natural sciences over the course of K-12 education.
      • Science in Personal and Social Perspectives (Std F)
        • Changes in environments
      • History and Nature of Science (Std G)
        • Science as a human endeavor
      • Physical Science (Std B)
        • Motions and forces
      • Earth and Space Science (Std D)
        • Structure of the earth system
      • History and Nature of Science (Std G)
        • Science as a human endeavor
      • Earth and Space Science (Std D)
        • Energy in the earth system
      • History and Nature of Science (Std G)
        • Science as a human endeavor

Team Assignment
<Event Team Study

This cycle you and your Event Team will build on the sphere to sphere interactions you identified last cycle to synthesize them into causal chains or causal matrices. You will use the resources listed under Readings, discuss your ideas in the event team discussion space, and then submit your team's work to ESSEA for a grade.



  • Read about the scenario.
  • Review the Team Event Study Rubric.
  • Serve as a "Sphere Expert" to your Event Team.
  • Read your teammates' summaries about the other individual sphere effects.
  • Identify intersecting and overlapping effects in your event team discussion space. Refer to An Example of an ESS Analysis reading if you would like to review causal relationships.
Upload to ESSEA your team's most accurate analysis of the Earth System interactions with reasoning and support and complete the team rubric.
Deadline: Friday, January 27 2017 11:59 PM (Eastern Time)
Upload Assignments

MY NASA DATA El Niņo Lesson (Cycle B)
This MY NASA DATA lesson explores the sea surface height anomaly during the historic El Niño of November 1997. Students correlate real satellite data to local weather.
Difficulty: intermediate

El Niņo & La Niņa (El Niņo-Southern Oscillation) ENSO (Cycle B)
Includes the latest information on ENSO, including links to latest official El Niño update.

USGS El Niņo Information (Cycle B)
This portal provides access to United States Geological Survey (USGS) publications related to El Nino, particularly the 2015-2016 El Nino season. There is an introductory article explaining El Nino, followed by a selection of resources on El Nino's damaging effects: floods, landslides, coastal erosion and salt water invasion, and long-term climate variations. There is also an extensive selection of links to non-USGS sites.

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