<P> Typically, this anomaly happens at irregular intervals of two to seven years, and lasts nine months to two years . The average period length is five years . When this warming occurs for seven to nine months, it is classified as El Niño "conditions"; when its duration is longer, it is classified as an El Niño "episode". </P> <P> There is no consensus on whether climate change will have any influence on the occurrence, strength or duration of El Niño events, as research supports El Niño events becoming stronger, longer, shorter and weaker . </P> <P> During strong El Niño episodes, a secondary peak in sea surface temperature across the far eastern equatorial Pacific Ocean sometimes follows the initial peak . </P> <P> ENSO conditions have occurred at two - to seven - year intervals for at least the past 300 years, but most of them have been weak . Evidence is also strong for El Niño events during the early Holocene epoch 10,000 years ago . </P>

Describe in detail the difference between el niño and la niña