El Ni�o is a naturally-occurring climatic event in the eastern Pacific which plays havoc with the world's weather system.

Under normal conditions warm ocean currents flow west towards the Asian continent and the underlying cold nutrient-rich water rises along the east Pacific coast of the Americas.

Every few years this trend reverses and the warmer currents flow east and the cooler ocean body sinks. Trade winds dwindle and sometimes reverse direction as the ocean temperature warms.

The changes to the weather can be quite dramatic, with increased rainfall in the southern United States and South America, and drought conditions in the west Pacific including Australia and Indonesia.

The atmosphere is also affected by the sea temperature as evaporation from the vast pool of warm water in the Pacific generates violent thunderstorms. These convection storms affect the high altitude winds of the jet stream leading to widespread weather changes.

Recent severe weather around the globe has been blamed on El Ni�o, and the World Bank and Inter-American Development Bank are already preparing more than $500m in loans to help Peru and Ecuador cope with the onslaught.