El Niño has arrived when temperatures in the eastern Pacific Ocean along the equator west of South America warm by at least half a degree Celsius (0.9 Fahrenheit) above normal
La Niña has arrived when temperatures in the eastern Pacific Ocean along the equator west of South America cool by at least half a degree Celsius (0.9 Fahrenheit) below normal
The last reversal was about 780,000 years ago. Reversals are not instantaneous; they happen over a period of hundreds to thousands of years, though recent research indicates that at least one reversal could have taken place over a period of one year.
29,031.7 feet or 8,848.86 meters