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El Niño (meaning "Christ child") is a periodic climatic event described by the warming of surface water in the Southwestern Pacific and weakening or reversal of equatorial trade winds. The El Niño-Southern Oscillation (ENSO) is a dominant force that affects global climate patterns. It is especially pronounced in the central and eastern equatorial Pacific regions of South America and Australia. ENSO events occur, on average, every two to seven years. These events are highly variable both in frequency and intensity, however, and their origins are still unknown to science.
During ENSO events, the classic Walker Cell either weakens or reverses, which leads to warm water propagating across the Pacific. This warm, low pressure system rises in the Eastern Pacific, which brings increased rain and flooding to Chile and Peru. Along the coast of South America, there is reduced nutrient upwelling. The colder, nutrient rich water does not rise to the surface, which leads to fishery collapse.
Across the Pacific Ocean, in Australia, the opposite processes occur. Descending low pressure systems led to a reduction in precipitation. This places Australia at risk for both drought and forest fires. Drought conditions in Asia have led to sever famine in China and India over the past few centuries.
Often increased precipitation, flooding, and weakening of trade winds are typical patterns for an El Niño event. With the warming of the sea surface temperatures and slowing of trade winds, fisheries start to collapse, and there is a positive feedback of other ecosystems failing. El Niño events have increased dramatically over the past 50 years and it is believed to be induced by anthropogenic factors.