Geography lessons

El Nino

El Nino is Spanish for the infant Jesus.  Peruvian fisherman first used the term to describe the appearance of a warm ocean current during Christmas.

El Nino refers to the reversal of ocean currents across the Pacific Ocean, so that warmer waters flow back to eastern Pacific resulting in heavy rains and floods in Peru and Chile and California, whilst cooler water upwells in the western Pacific causing drought in Australia and Indonesia.  El Nino is characterised by warmer water surface temperatures in the central and eastern tropical (equatorial) Pacific Ocean and weaker Pacific trade winds.

Southern Oscillation Index (SOI)

The strength of the Pacific trade wind is measured by the Southern Oscillation Index (SOI).  SOI is calculated by measuring the difference in air pressure between Tahiti in the eastern Pacific and Darwin in the western Pacific.

  • Low SOI=normal conditions
  • Negative SOI (below -15) = El Niino
  • Positive SOE (above +10) = La Nina

The 1997/1998 El Nino

See what happened with our oceans during the El Nino of 1998 from a computer model archive at Sea level viewer from NASA

The extreme El Nino event of 1997 – 1998 resulted in drought for most continents of Earth.  This year was dubbed by the Worldwide Fund for Nature (WWF) as “The Year the World Caught Fire”.  Fires burnt on every continent with the greatest devastation caused by millions of hectares of ancient rainforests being destroyed by fire in Borneo.

Ecological effects of El Nino:

  • Loss of habitat and animal life as a result of drought and bushfires.
  • With the El Nino warm current, the  cold current (the “humbolt”) carrying nutrients leading to the growth of phytoplankton as food for anchovies and sardines fails to upwell, the fish move south and there is a loss of fish stock off the coast of Peru and Ecuador.  Birdlife, sealions and fishermen from Peru and Ecuador go hungry.

Climate Change debate

  • Will El Nino events intensify in effect or in regularity as a result of manmade climate change?


Bureau of Meteorology

Flannery, Tim. (2007) We Are the Weather Makers.

Parker, B., Lanceley, K., Owens, D., Fitzpatrick, R. (2008) Geography for Global Citizens (3rd ed.)


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