El Niño
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What El Niño is
El Niño is a climate pattern that can affect weather worldwide. It happens when ocean water in the central and eastern tropical Pacific Ocean becomes warmer than usual. This warmer water changes air movement in the atmosphere and as a result, weather patterns change in many parts of the world.
How El Niño happens
During normal weather conditions, easterly winds (or tropical easterlies), move warm surface water westward across the tropical Pacific Ocean. This causes deep, cold water to rise to the surface along the equator and near the South American coast. As these conditions continue:
- the warm ocean water in the western Pacific heats the air above it, causing the air to rise
- cooler air sinks over the eastern Pacific and along the west coast of South America
During El Niño, trade winds weaken or change direction. This allows the warm water in the western Pacific to spread eastward and makes cold water less able to rise to the surface.
As a result:
- ocean temperature rises toward the west coast of South America
- heat and moisture increase over the eastern Pacific, including over coastal Ecuador and Peru
- rainfall shifts toward the central and eastern Pacific
- weather conditions get drier in the western tropical Pacific
How El Niño affects Canada
Canada is mostly affected by El Niño during winter and spring. El Niño often brings milder weather to western, northwestern and central Canada, while eastern Canada usually experiences lesser effects. El Niño may also reduce tropical storm activity in the Atlantic Ocean.
El Niño happens about every two to seven years and alternates with La Niña, a cooler ocean pattern.
Niño and climate change
Scientists continue to study the relationship between El Niño and climate change. Currently, how climate change may affect El Niño remains a matter of scientific debate. Further research is needed before scientists can provide confident answers.