Niño and Niña
The Humbolt ocean current goes north along the Peruvian coasts and pushes surface waters towards the open sea. This favours cold waters to go up to the surface. These waters are rich in nutrients that increase the presence of phytoplankton and fish. From the end of December to March-April a current moves to the south, warming the ocean surface water and determining the reduction of nutrients and fish. This warmer current is Niño, the Baby Jesus, as it starts at Christmas. In some years the warming up can be longer than a year and with temperatures increasing by 7°C instead of the usual 1-2°C. During these periods serious damages to the marine environment and fishing industry occur (like anchovy fishing in Peru).
The causes for this anomalous situation are many: wind direction changes along the Equator, changes in atmospheric circulation that cause heavy rain (and floods) in coastal deserts of Peru, while in African, Indian and Australian they provoke long drought periods. Generally this phenomenon repeats every 2 or 10 years.
Alternatively, some years can be characterized by intense cooling, accompanied by heavy rain in areas like India, Australia and Sahel. This episodes are called Niña.