El Niño / La Niña-Southern Oscillation (ENSO)

You can find research, forecasts and observations on NOAA's main page on El Niño. You can find current conditions on the ENSO page at NOAA's Climate Prediction Center and an informative article about ENSO on Wikipedia containing lots of source material at the bottom of the page.

El Niño's Past

3000 B.C: Chemical signatures of warmer sea surface temperatures & increased rainfall caused by El Niño appear in coral specimens at least this old. Some researchers claim to have found coral records that hold evidence of El Niño cycles more than a 100,000 years ago.
1500 A.D.:Fisherman off the coast of Peru discover that periodic warm waters hold down their anchovy catch. Peruvian farmers notice the warm waters lead to increased rainfall, transforming normally barren areas into fertile farmland. The warm current is dubbed El Niño after the child Jesus, because it usually appears around Christmas.
1700-1900: European sailors make sporadic attempts at documenting the phenomenon. Scientists become interested in identifying its cause.
1891: Dr. Luis Carranza, a Peruvian geographer, publishes an article associating El Niño with unusual rain patterns & suggests it exerts "a very great influence on the climate conditions of (this) part of the world."
1923: British scientist Sir Gilbert Walker discovers that when air pressure is high in the Pacific, it is low in the Indian Ocean from Africa to Austrailia, and vice versa. His find, which he names the Southern Oscillation, is the first indication that weather conditions in distant parts of the tropical Pacific are connected.
1969: Professor Jacob Bjerknes of the University of California at Los Angeles comes up with the first detailed description of how El Niño -- now officially known as El Niño/Southern Oscillation or ENSO for short -- works.
1982-83: The strongest El Niño ever recorded wreaks havoc around the world. Related floods, droughts & wildfires kill about 2,000 people worldwide. Damage is estimated at $13 Billion. In the United States, the first widespread attempts to study the phenomenon begin.
1997-1998: An El Niño more powerful than the record 1982-83 event develops in the Pacific. Warnings are issued in mid 1997,& emergency preparedness conferences are convened. By march 1998, El Niño-related flooding & tornadoes have killed dozens in Florida & the rest of the U.S. Georgia experienced a tornado killing over a dozen people.
So what causes El Niño? Periodically, trade winds near the equator weaken or reverse direction, forcing a huge current of warm water that seesaws back & forth across the Pacific.The warm waters pool off the coast of Peru & raise the water 3 to 5 degrees.

Click here for historical data from NOAA's Climate Prediction Center.

Graphic provided by Brian McNoldy