Q+A: Why do El Nino and La Nina trigger weather chaos?


The record floods sweeping Australia’s Queensland state are the result of a natural swing in Pacific Ocean temperatures that can trigger climate chaos around the globe.

Scientists say the floods are caused by one of the strongest La Nina episodes on record with experts forecasting it will last for several more months. The disaster, which has killed 16 people, could cut Australia’s economic growth by 1 percent, a central bank board member said.

Following are some questions and answers on the La Nina weather pattern and its sibling El Nino and their billion-dollar impacts on economies, reports Reuters.


El Nino, also called “Little Boy” or “Christ Child,” is a warming of ocean surface temperatures in the eastern and central Pacific.

Peruvian fishermen noticed the arrival of the warm waters occurred usually around Christmas time. The phenomena, which occurs every three to seven years, led to more rains in that part of South America and a drop in the fish catch.

Strong El Ninos can lead to a dramatic weakening of the trade winds that blow west across the Pacific, triggering drought in Southeast Asia and Australia. Some El Ninos can also affect the Indian monsoon by reducing rainfall, threatening crops and livelihoods.


Globally, El Nino can trigger above average rains in northern Peru and Bolivia, drought in Southeast Asia, Australia, India and northeast Brazil, cyclones in the central Pacific and stormy weather in southern and western United States.

El Ninos also tend to cut the number of Atlantic hurricanes but boost the number of storms in the eastern Pacific.

Globally, the result can be disastrous in terms of loss of human life, infrastructure, crops and business. In Australia, strong El Ninos can slash wheat crop output, threaten water supplies by cutting river flows, shrink city reservoirs and dry out forests, triggering deadly bush fires.

Major El Ninos occurred in 1982-82 and 1997-98 but the weak El Nino of 2002-2003 also led to severe drought in Australia.


La Nina, or “Little Girl,” is the opposite to El Nino, leading to abnormally cool ocean temperatures in the eastern and central Pacific.

This triggers stronger trade winds across the Pacific that pile up very warm warmers in the western Pacific and around northern Australia.