El Niño and its Effects


Diagram showing the principle of the El Niño in the central Pacific. Colors indicate temperature, with red being warmest and blue coldest. In normal, non-El Niño conditions (top panel of schematic diagram), 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 1/2meterhigher at Indonesia than at Ecuador. During El Niño (bottom panel of the schematic diagram), 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, thereby bringing an end to nutrient upwelling. (From: NOAA). For more information on El Niño go to: Scripps Institution of Oceanography
El Niño - A Definition
Unusual rainfall in Southern California — and in Peru and Chile — are commonly tied to a climatic condition that involves the entire Pacific and is referred to as "El Niño." The term, as applied to climate, originated with fishermen in Ecuador and Peru who used “El Niño” to mean the “Christ Child” as a way to describe a warm current that appears every few years in their fishing areas, around Christmas.

What exactly is meant climatically by saying, "We have an El Niño situation?” Normally, the cold Peru Current (or Humboldt Current) flows offshore from south to north. (It is a kind of mirror image of the California Current, but colder and stronger.) Associated with this cold current is a process called "coastal upwelling," or the rising of cold subsurface water. This upwelling water is rich in nutrients (nitrate and phosphate). These nutrients stimulate the growth of microscopic green algae (phytoplankton), which then serve as food for small animals (zooplankton). The plankton is eaten by fish (mainly anchovies and sardines), which are in turn caught by bigger fish, sea lions, birds, and people. During an El Niño situation, when the warm current appears, upwelling ceases and phytoplankton production is greatly diminished and the fish move to colder regions farther south (or they starve).

El Niño – A Larger Picture
The appearance of the warm current off Peru is a spillover from a much larger event: a general warming in the eastern tropical Pacific during certain years. This warming results from a weakening of the trade winds and a movement of water from the west-equatorial warm pool (which has been piled up by the trades) toward the east (See also the glossary for "El Niño" and "Warm pool").


A summary of the cost estimates in US Dollars for the 1982-1983 El Niño, which was the strongest such event recorded over the past 50 years. Although El Niño events vary in intensity, the costs from even the smallest event can be staggering. (From: NASA)
El Niño and its Devastating Effects
An El Niño situation occurs every three or four years or so, mainly in December, and is devastating to the fishing economies of Ecuador and Peru. Birds, sea lions and fishermen go hungry because there are not enough fish to go around. Also, torrential rainfall in the coastal zone frequently accompanies the offshore warming, causing devastating floods (as happened in 1982-1983). See below for a summary of costs associated with the 1982-1983 El Niño.

El Niño and California
In the North Pacific, the Aleutian low-pressure region (over the Aleutian Islands chain to the southwest of Alaska) and the NE Pacific high-pressure region off California characterize normal conditions. When the trade winds weaken and the eastern Pacific warms up, the Aleutian low-pressure center tends to expand southward. The high-pressure cell off California weakens, and the California Current slows and warms. Fisheries collapse. Kelp forests suffer. Baby sea lions starve. Warm, moist air is widely available, favoring development of storm centers. The jet stream in the upper troposphere and the lower stratosphere, which runs along the boundary of arctic and tropical air, moves farther south. Storm tracks move south along with it, and increasingly impinge on the coast of our region. In summary, extraordinary events of precipitation in our region (which produce high stream flow or flooding) are commonly associated with El Niño conditions, when the eastern Pacific is unusually warm. Winter storms, generated in the North Pacific, move farther south than at "normal" times. Also, they have the opportunity to pick up moist tropical air along the way. Absent the offshore high (which acts as a road block), the storm systems can invade our region and dump their load.


El Niño and its effect on the North Pacific, associated with eastern displacement of warm water (red) and associated rain clouds (gray). The warmer equatorial waters heat the atmosphere over time periods measured in months. The atmosphere responds to this heating by producing alternating patterns of low and high pressure, including the low pressure centered just to the southwest of Alaska and another centered over the southeastern United States. (From: NASA)
El Niño and Climate Change
Although El Niño events are not new (there is evidence they have been occurring for hundreds of years), a distinct change in the behavior of this event beginning in the mid-1970’s has some worried that human-induced climate change may be having its effect. These recent changes include two “extreme” El Niño events (the strongest in this century, the 1982 to 1983 event and the longest of this century, the 1990 to 1995 event) and an increased frequency of El Niño relative to the past 50 years. As is the case with most attempts to pen a modern day observation to global warming, this evidence cannot rule out “natural variation.” Periods of high El Niño activity have occurred before, as for example from 1880 to 1925. That being said, some computer models of climate change predict precisely what is being observed today: increased likelihood of El Niño (with one study suggesting an increase of once every five years to once every three years); warming of the tropical Pacific with greater warming in the east than in the west (a pattern generally associated with El Niño); and a possible increase in El Niño severity. In so much as El Niño is a natural phenomena, it is something we need to live with, just as we do with earthquakes and hurricanes. However, if the current El Niño trend continues, the consequences could take a heavy toll on the entire world, disrupting everything from the U.S. insurance industry to the prospect for worldwide sustainable development.